Timeline of Chemical Science
The seven Metals of Antiquity were
- Gold (ca) 6000 BC
- Copper,(ca) 4200 BC
- Silver,(ca) 4000 BC
- Lead, (ca) 3500 BC
- Tin, (ca) 1750 BC
- Iron smelted, (ca) 1500 BC
- Mercury, (ca) 750 BC
Out of the Metals of Antiquity, five metals, gold, silver, copper, iron, and mercury can be found in their native states, but the occurrence of these metals was not abundant.
Ores and Minerals:
Certain metals, notably tin, lead, and at a higher temperature, copper, can be recovered from their ores by simply heating the rocks in a fire or blast furnace, a process known as smelting.
In the Near East, about 3500 BC, it was discovered that by combining copper and tin, a superior metal could be made, an alloy called bronze. This represented a major technological shift known as the Bronze Age.
A few minerals are chemical elements, including sulfur, copper, silver, and gold, but the vast majority are compounds. The classical method for identifying composition is wet chemical analysis, which involves dissolving a mineral in an acid such as hydrochloric acid (HCl). The elements in the solution are then identified using colorimetry, volumetric analysis, or gravimetric analysis.
On the Nature of Metals:
In 1500 AD, the first printed book dedicated to mining engineering, called the Nutzlich Bergbuchleyn (The Useful Little Mining Book”) by Ulrich Rulein von Calw, was published. The most important works in this genre were, however, the twelve books of De Re Metallica by Georgius Agricola, published in 1556.
Agricola next describes that gold, silver, copper, and mercury can be found as native metals, the others very rarely. Gold and silver ores are described in detail. Agricola then states that it is rarely worthwhile digging for other metals unless the ores are rich. Gems are found in some mines, but rarely have their own veins, lodestone is found in iron mines and emery in silver mines. Various minerals and colours of earths can be used to give indications of the presence of metal ores. The actual mineworking varies with the hardness of the rock, the softest is worked with a pick and requires shoring with wood, and the hardest is usually broken with fire. Iron wedges, hammers, and crowbars are used to break other rocks.
This book describes smelting, which Agricola describes as perfecting the metal by fire. The design of furnaces is first explained. These are very similar for smelting different metals, constructed of brick or soft stone with a brick front and mechanically driven bellows at the rear. At the front is a pit called the fore-hearth to receive the metal. The furnace is charged with beneficiated ore and crushed charcoal and lit. In some gold and silver smelting a lot of slag is produced because of the relative poverty of the ore and the tap hole has to be opened at various times to remove different slag materials. When the furnace is ready, the forehearth is filled with molten lead into which the furnace is tapped. In other furnaces, the smelting can be continuous, and lead is placed into the furnace if there is none in the ore. The slag is skimmed off the top of the metal as it is tapped. The lead containing the gold is separated by cupellation, and the metal-rich slags are re-smelted. Other smelting processes are similar, but lead is not added. Agricola also describes making crucible steel and distilling mercury and bismuth in this book.
Agricola describes parting silver from gold in this book by using acids. He also describes heating with antimony sulphide (stibium), which would give silver sulphide and a mixture of gold and antimony. The gold and silver can then be recovered with cupellation. Gold can also be parted using salts or using mercury. Large-scale cupellation using a cupellation hearth is also covered in this book
This book describes
separating silver from copper or iron. This is achieved by adding large
amounts of lead at a temperature just above the melting point of lead.
The lead will liquate out with the silver. This process will need to be
repeated several times. The lead and silver can be separated by
cupellation.
This describes the preparation of what Agricola calls "juices": salt, soda, nitre, alum, vitriol, saltpeter, sulphur, and bitumen. Finally, glass making is covered. Agricola seems less secure about this process. He is not clear about making glass from the raw ingredients but clearer about remelting glass to make objects.
Although Agricola died in 1555 AD, the publication was delayed until the completion of the extensive and detailed woodcuts one year after his death.
Making sea salt:
Sea salt is made by evaporating seawater, but this is not straightforward. Between 100% and 50% first the calcium carbonate (CaCO3= limestone) precipitates out, which is chalk and not desirable. Between 50% and 20%, gypsum precipitates out (CaSO4.2H2O), which also tastes like chalk. Between 20% and 1% sea salt precipitates (NaCl) but going further, the bitter potassium and magnesium chlorides and sulfates precipitate, which is to be avoided, unless for health reasons. In commercial salt production, the water is led through various evaporation ponds, to achieve the desired result. Note that this process has also happened where large lakes dried out, laying down the above salts in the above sequence. Note that normal seawater is undersaturated with respect to all its salts, except for calcium carbonate which may occur in a saturated or near-saturated state in surface waters.
Most of the world's reserves of potassium (K) were deposited as seawater in ancient inland oceans.
After the water evaporated, the potassium salts crystallized into beds
of potash ore. These are the locations where potash is being mined
today. The deposits are a naturally occurring mixture of potassium
chloride (KCl) and sodium chloride (NaCl). Over time, as the surface of
the earth changed, these deposits were covered by thousands of feet of
earth.
Rare Earth Elements
Monazite is a rare phosphate mineral with a chemical composition of (Ce,La,Nd,Th)(PO4,SiO4). It usually occurs in small isolated grains, as an accessory mineral in igneous and metamorphic rocks such as granite, pegmatite, schist, and gneiss. These grains are resistant to weathering and become concentrated in soils and sediments downslope from the host rock. When in high enough concentrations, they are mined for their rare earth and thorium content.
"Rare earths are relatively abundant in the Earth's crust, but discovered minable concentrations are less common than for most other ores. U.S. and world resources are contained primarily in bastnäsite and monazite. Bastnäsite deposits in China and the United States constitute the largest percentage of the world's rare-earth economic resources, while monazite deposits in Australia, Brazil, China, India, Malaysia, South Africa, Sri Lanka, Thailand, and the United States constitute the second largest segment.
More than 90% of the crust is composed of
silicate minerals. The most abundant silicates are feldspars
(plagioclase (39%) and alkali feldspar (12%)). Other common silicate
minerals are quartz (12%) pyroxenes (11%), amphiboles (5%), micas (5%),
and clay minerals (5%). The rest of the silicate family comprises 3% of
the crust. Only 8% of the crust is composed of non-silicates —
carbonates, oxides, sulfides, etc.
Clay minerals are too small to be
shown individually. Even with a light microscope, you will see only mud
or dust depending on whether these minerals are wet or dry. Clay
minerals are silicates that are the products of weathering of other
silicate minerals, mostly feldspars.
Chemistry- Phase-I
The Royal Society was founded in London in 1660. Robert Boyle became the head of the Royal Society.
Robert Boyle (1627-1691) was an Anglo-Irish natural philosopher, chemist, physicist, and inventor. He is considered one of the founders of modern experimental science and is best known for Boyle's law, which describes the inverse relationship between the pressure and volume of a gas, assuming the temperature remains constant.
He gave Boyle’s law of gases, PV=RT
He advocated for an experimental and evidence-based approach to scientific inquiry and rejected reliance on ancient authorities and unverified traditions.
Boyle's work covered a wide range of scientific disciplines, including physics, chemistry, medicine, and biology. He conducted numerous experiments and made significant contributions to various fields.
In chemistry, Boyle is known for his studies on the behavior of gases and the concept of chemical elements. His book "The Sceptical Chymist" (1661) challenged the prevailing theories of alchemy and laid the groundwork for modern chemistry.
Robert Boyle gave the concept of elements, Acids, and Bases.
Professor Joseph Black discovered fixed air (CO2).
Joseph Black (1728-1799) was a Scottish physicist and chemist known for his discoveries in the field of heat and the identification of carbon dioxide. He played a significant role in the development of the concept of latent heat and is considered one of the pioneers of modern thermodynamics.
Black's research on carbon dioxide also played a crucial role in the development of chemistry. He identified the gas produced during the reaction of acids with certain carbonates, noting its role in the formation of carbonates and the process of respiration. Black's work on carbon dioxide laid the groundwork for the understanding of gases and their role in chemical reactions.
One of Black's most notable contributions was his work on heat and the concept of latent heat. Through experiments, he discovered that when a substance undergoes a change of state, such as melting or vaporization, heat is absorbed or released without a corresponding change in temperature. He termed this heat "latent heat" and recognized its significance in understanding the behavior of substances during phase transitions.
Joseph Black's work laid the foundation for the development of thermodynamics and had a profound impact on the fields of chemistry and physics. His discoveries and concepts continue to be fundamental in our understanding of heat, energy, and the behavior of substances.
Henry Cavendish discovered inflammable air, (later named as Hydrogen by Lavoisier).
Henry Cavendish (1731-1810) was a British scientist known for his groundbreaking contributions to physics and chemistry. He is particularly recognized for his work on the composition of air, the discovery of hydrogen, and the determination of the gravitational constant.
In 1766, Cavendish also discovered a new gas that he referred to as "inflammable air." This gas is now known as hydrogen. Cavendish described its properties, including its lightness and combustibility, and recognized its potential importance. However, he did not fully grasp the significance of his discovery in terms of its role in chemistry and energy until later.
Scheele discovered fire air (oxygen).
Carl Wilhelm Scheele (1742-1786) was a Swedish chemist known for his significant contributions to the field of chemistry. He made several key discoveries, including the identification of numerous chemical elements and the characterization of important compounds.
Scheele was born in Sweden and worked as an apprentice in a pharmacy, which laid the foundation for his interest in chemistry. Despite lacking formal education, he conducted numerous experiments and made important scientific observations.
One of Scheele's most notable achievements was the discovery and characterization of several chemical elements. He is credited with independently discovering oxygen in 1772, although his publication on the discovery was delayed, and therefore, the recognition went to Joseph Priestley and Antoine Lavoisier. Scheele also discovered several other elements, including chlorine, manganese, barium, and tungsten, and contributed to the understanding of their properties and reactions.
Furthermore, Scheele was involved in the identification and synthesis of various important compounds. He isolated and described organic acids such as tartaric acid, malic acid, and lactic acid, and he was the first to prepare citric acid. His work also included investigations into the properties of numerous chemicals, including hydrogen sulfide, arsenic, and prussic acid (hydrogen cyanide).
Joseph Priestley discovered dephlogisticated air (Oxygen).
Joseph Priestley (1733-1804) was an English clergyman, chemist, and philosopher who is best known for his pioneering work in the field of chemistry and his discovery of several important gases. He made significant contributions to the understanding of gases, the nature of combustion, and the role of oxygen in respiration.
One of Priestley's most significant discoveries was the identification and isolation of several gases. In 1774, he conducted an experiment in which he focused sunlight on a sample of mercury oxide, resulting in the release of gas. This gas, which Priestley called "dephlogisticated air," was later recognized as oxygen. Priestley's experiments on gases also led to the discovery of other important gases, including nitrous oxide (laughing gas), carbon monoxide, sulfur dioxide, and ammonia.
Antoine Lavoisier (1743-1794) made significant contributions to the field of chemistry during the 18th century.
Lavoisier gave the theory of combustion and the role played by Oxygen in combustion. He gave the law of conservation of mass in a chemical change. He made a list of the known 23 elements. He used chemical balance to make accurate calculations. He disproved the existence of Phlogiston as an element. He named the elements systematically.
Antoine-Laurent de Lavoisier was a French chemist often referred to as the "Father of Modern Chemistry." He is best known for his work in the field of chemical nomenclature, the law of conservation of mass, and the discovery of the role of oxygen in combustion and respiration.
Lavoisier revolutionized the field of chemistry by introducing a systematic and rigorous approach to scientific experimentation. He conducted meticulous and quantitative experiments, emphasizing precise measurements and observations. He also developed a standardized system for naming chemical elements and compounds, which is still in use today.
One of Lavoisier's most significant contributions was his recognition of the importance of oxygen in chemical reactions, particularly combustion. He performed experiments that demonstrated that combustion requires the presence of oxygen and that oxygen combines with substances during the process. His work on the role of oxygen in respiration and the understanding of the process of metabolism further contributed to our knowledge of human physiology.
Lavoisier also played a crucial role in disproving the phlogiston theory, a prevailing theory of combustion at the time. He showed that combustion involved the combination of substances with oxygen rather than the release of a hypothetical substance called phlogiston. His experiments and theories laid the foundation for the modern understanding of chemical reactions and the concept of the conservation of mass.
Furthermore, Lavoisier conducted extensive research on the properties and reactions of numerous chemical elements. He contributed to the identification and understanding of elements such as hydrogen, nitrogen, and carbon. He also investigated the composition of water, demonstrating that it consists of hydrogen and oxygen.
Lavoisier's scientific contributions were extensive and transformative. His work elevated chemistry to a quantitative science and paved the way for future advancements in the field.
Alessandro Volta invented the Voltaic Pile, a primary battery cell.
The Voltaic cell consists of two electrodes, an anode (negative electrode) and a cathode (positive electrode), immersed in an electrolyte solution. The electrodes are typically made of different metals or metal compounds that have different affinities for electrons. When the electrodes are connected by a wire, a chemical reaction takes place at the interface of the electrodes and the electrolyte, causing a flow of electrons from the anode to the cathode.
Alessandro Volta (1745-1827) was an Italian physicist and chemist who is best known for his invention of the electric battery, which revolutionized the field of electricity and contributed to the development of early electrical devices.
Volta was born in Italy and pursued a career in physics and chemistry. He conducted experiments and made significant discoveries in various scientific fields. His most famous invention, the voltaic pile or battery, was created in 1800. It consisted of alternating layers of zinc and copper discs separated by cardboard soaked in an electrolyte solution. The voltaic pile provided a continuous flow of electric current and was the first device capable of producing a reliable and steady source of electricity.
The invention of the battery had a profound impact on the study of electricity and led to advancements in the field of electrochemistry. Volta's work challenged the prevailing theory of electricity at the time, which posited that electricity could only be produced by living organisms. His experiments demonstrated that electricity could be generated chemically, opening up new possibilities for harnessing electrical energy.
Volta's invention of the battery also sparked the development of numerous electrical devices. It laid the foundation for the design and construction of early telegraphs, electromagnets, and other electrical apparatus. The unit of electric potential, the volt, was named in his honor.
Joseph Louis Proust announced that in a chemical combination, elements always combine in a fixed ratio by mass, to form compounds. this is called, the law of constant composition or the law of definite proportion.
Joseph Louis Proust (1754-1826) was a French chemist who made significant contributions to the understanding of chemical compounds and the development of stoichiometry. He is best known for his formulation of the law of definite proportions, also known as Proust's Law.
Proust's most famous contribution is the law of definite proportions, which states that a given compound always contains the same elements in the same proportion by mass. In other words, the ratio of the masses of the constituent elements in a chemical compound is constant. This law contrasted with the prevailing theory of the time, which suggested that elements could combine in any proportion.
Through meticulous experimentation, Proust analyzed various chemical compounds and consistently found that their elemental composition followed fixed ratios. This fundamental principle of stoichiometry provided a basis for understanding the nature of chemical compounds and laid the groundwork for future advancements in atomic theory.
In addition to his work on stoichiometry, Proust also made important contributions to the field of metallurgy. He conducted experiments on the behavior of metals during heating and cooling, studying the phenomenon of metal oxidation and the formation of metal oxides.
Proust's work on the law of definite proportions contributed to the development of the atomic theory proposed by John Dalton. Dalton's theory expanded on Proust's ideas, suggesting that chemical elements are made up of atoms that combine in specific ratios to form compounds.
John Dalton gave the concept of Atom, as the smallest particle of an element that takes part in a chemical reaction. He compiled a list of atomic weights for different elements.
John Dalton (1766-1844) was an English chemist, physicist, and meteorologist who is best known for his development of atomic theory. His work revolutionized our understanding of matter and laid the foundation for modern chemistry.
Born in England, Dalton began his scientific career as a teacher and researcher. He conducted numerous experiments and made significant contributions to various scientific fields, including chemistry, physics, and meteorology.
Dalton's most significant achievement was the development of atomic theory, which he presented in his book "A New System of Chemical Philosophy" published in 1808. According to Dalton's atomic theory, all matter is composed of indivisible particles called atoms, which are unique to each element. He proposed that atoms combine in fixed ratios to form compounds and that chemical reactions involve the rearrangement of atoms.
Furthermore, Dalton introduced the concept of relative atomic weights and recognized that atoms of different elements have different masses. He established a system of assigning atomic weights to elements based on their relative masses, allowing for the determination of the composition of chemical compounds.
Dalton's atomic theory provided a coherent framework for understanding the behavior of gases, the principles of chemical reactions, and the nature of elements and compounds. It had a profound impact on the development of chemistry and was later expanded upon and refined by other scientists.
John Dalton's contributions to the field of chemistry, particularly his development of atomic theory, revolutionized the way we understand matter and chemical reactions. His work laid the foundation for modern chemistry and influenced scientific thinking for generations to come. He is recognized as one of the most influential scientists in the history of chemistry.
1800-For the
first time, water was decomposed into hydrogen and oxygen gases using
electrolysis of water, by applying a DC power supply in order to force a
chemical decomposition. This proved that water is not an element.
Electrolysis: Electrolysis is a commonly used method to decompose water. It involves passing an electric current through water, which causes the water molecules to split into hydrogen and oxygen gases. Two electrodes, typically made of inert materials such as platinum or graphite, are placed in the water. The positive electrode, called the anode, attracts negatively charged hydroxide ions (OH-) and undergoes oxidation, releasing oxygen gas (O2). The negative electrode, called the cathode, attracts positively charged hydrogen ions (H+) and undergoes reduction, producing hydrogen gas (H2).
Jacob Berzelius(a disciple of Dalton) determined the atomic weights of many elements. he used symbols to write different elements. This simplified method was used to write the molecular formulae for different compounds. He classified elements as electro-positive and electro-negative. (metals and non-metals). many new elements were discovered in his laboratory.
Jöns Jacob Berzelius, a Swedish chemist, made significant contributions to the field of chemistry in the 19th century, including the determination of atomic weights. Berzelius developed a system to assign relative atomic weights to elements based on their chemical reactions and proportions.
Here are some atomic weights assigned by Berzelius:
- Hydrogen (H): 1.00
- Oxygen (O): 8.00
- Nitrogen (N): 14.00
- Carbon (C): 12.00
- Sulfur (S): 16.00
- Chlorine (Cl): 35.50
- Sodium (Na): 23.00
- Potassium (K): 39.00
- Calcium (Ca): 40.00
- Iron (Fe): 56.00
Humphry Davy built a large Voltaic pile and applied it on molten salts to isolate many new elements, like potassium, sodium, Calcium, magnesium, etc. He announced chlorine, as an element. he popularised chemistry through his lectures and demonstrations.
Humphry Davy, an English chemist, and inventor, made significant contributions to the field of chemistry in the late 18th and early 19th centuries. He conducted pioneering work on electrolysis and made several important discoveries, including the isolation of several new elements.
Here are some of the new elements discovered by Humphry Davy:
- Potassium (K) and Sodium (Na): In 1807, Davy used electrolysis to isolate potassium and sodium from their respective compounds. He passed an electric current through molten potassium hydroxide and sodium hydroxide, causing the metals to be liberated at the cathode. This marked the first time these alkali metals were isolated in pure form.
- Barium (Ba), Calcium (Ca), Magnesium (Mg), and Strontium (Sr): Davy also used electrolysis to isolate these alkaline earth metals. By passing an electric current through their molten salts, he succeeded in obtaining pure barium, calcium, magnesium, and strontium.
- Boron (B): In 1808, Davy discovered boron by reducing boron oxide with potassium. Although he did not isolate it in its pure form, his work laid the foundation for the subsequent isolation and characterization of boron.
It's worth noting that Davy's discoveries were often based on his use of electrolysis, which allowed him to isolate metals from their compounds. His work not only contributed to the discovery of new elements but also helped establish the concept of chemical elements as distinct substances. Davy's contributions were highly influential in shaping the field of chemistry during his time and laid the groundwork for future advancements in the understanding of chemical elements and their properties.
Michel Faraday gave the laws of electrolysis. In an electrolysis process, the quantity of chemical change produced is directly proportional to the electric energy supplied from an external source. he gave the concept of molecular weight and equivalent weight.
Faraday's laws of electrolysis, formulated by the English scientist Michael Faraday in the 1830s, describe the quantitative relationships between the amount of substance transformed during an electrolytic reaction and the electric current passed through the electrolyte. These laws are fundamental principles in electrochemistry. Faraday's two laws of electrolysis are as follows:
- Faraday's First Law of Electrolysis: The amount of chemical substance (in moles) liberated or deposited at an electrode during electrolysis is directly proportional to the quantity of electricity (in coulombs) passed through the electrolyte.
Mathematically, this can be expressed as:
m = zFQ
Where: m = mass of substance liberated or deposited (in grams) z = electrochemical equivalent (the amount of substance liberated per unit charge) F = Faraday's constant (96,485 C/mol) Q = quantity of electricity passed (in coulombs)
- Faraday's Second Law of Electrolysis: When the same quantity of electricity passes through different electrolytes, the masses of the substances liberated or deposited at the electrodes are directly proportional to their respective chemical equivalent weights.
Mathematically, this can be expressed as:
m₁/m₂ = E₁/E₂
Where: m₁, m₂ = masses of substances liberated or deposited E₁, E₂ = chemical equivalent weights of the substances
The chemical equivalent weight is the amount of substance (in grams) that is equivalent to one mole of electrons exchanged during the redox reaction.
Faraday's laws provide a quantitative understanding of the relationship between electricity and chemical reactions during electrolysis. They are crucial for calculating the amount of substance produced or consumed in an electrolytic cell and have practical applications in various electrochemical processes, such as electroplating, metal refining, and electrochemical synthesis.
Chemical Society was founded in London.
The Chemical Society of London was a learned society established in 1841 to promote the study of chemistry. It was one of the precursor organizations to the Royal Society of Chemistry (RSC), which is the professional body for chemists in the United Kingdom today.
The Chemical Society of London played a pivotal role in advancing the field of chemistry and facilitating communication among chemists during the 19th and early 20th centuries. It provided a platform for scientists to present their research findings, exchange ideas, and discuss scientific advancements in the field of chemistry.
in 1860, Kekule organized the first chemical meet in Karlsruhe in Germany. Cannizero spoke on chemical science and a list of atomic weights was supplied to the participants. he suggested participants to use the Berzelius atomic weights and use Avogadro's concept of molecular concept of gases.
The Karlsruhe Congress, also known as the Karlsruhe Conference or the Karlsruhe Congress on Elementary Principles of Chemical Processes, was a significant scientific event held in Karlsruhe, Germany, in September 1860. The congress brought together leading chemists and physicists of the time to discuss and advance the understanding of chemical principles and atomic theory.
The Karlsruhe Congress was organized by the German chemist August Kekulé and was attended by renowned scientists such as Alexander von Humboldt, Gustav Kirchhoff, Robert Bunsen, and Hermann von Helmholtz, among others. The participants aimed to address key questions and challenges in the emerging field of chemistry and develop a cohesive framework for chemical theory.
During the congress, discussions focused on topics such as atomic theory, chemical structure, and the determination of atomic weights. The participants aimed to reconcile and unify existing ideas, laying the foundation for the development of modern chemical concepts. One significant outcome of the congress was the recognition of the importance of valence, which provided a basis for understanding the bonding and arrangement of atoms in molecules.
The Karlsruhe Congress played a crucial role in the advancement of chemistry, leading to significant breakthroughs and advancements in chemical theory. It helped establish a common language and understanding among chemists and contributed to the development of a systematic and rigorous approach to the study of chemical processes. The congress is considered a milestone in the history of chemistry and continues to be recognized as a significant event in scientific history.
Saibarian Chemist Mendeleyv constructed a periodic table of elements. He arranged elements with increasing atomic weights in rows and columns. he grouped similar elements together in a column.
The Periodic Table of Elements is a tabular arrangement of chemical elements organized based on their atomic number, electron configuration, and recurring chemical properties. It was first developed by Dmitri Mendeleev, a Russian chemist, in the 1860s. Mendeleev's periodic table is considered one of the most significant achievements in the history of chemistry.
Mendeleev's approach to developing the periodic table involved arranging the known elements in order of increasing atomic weight while also considering their chemical properties. He noticed that when the elements were arranged in this manner, certain patterns and periodicities emerged. Mendeleev left gaps in his table for elements that were yet to be discovered and accurately predicted the properties of these missing elements based on their positions in the table.
Some key features of Mendeleev's periodic table include:
- Periods: Mendeleev grouped elements into rows called periods. Each period represents the energy levels (shells) occupied by electrons in the atoms of the elements.
- Groups: Mendeleev also classified elements into columns called groups. Elements within the same group have similar chemical properties and share the same number of valence electrons.
- Periodic Law: Mendeleev's periodic table demonstrated the periodic law, which states that the chemical and physical properties of elements are periodic functions of their atomic numbers.
Mendeleev's periodic table was a groundbreaking concept that provided a systematic organization of elements and offered a foundation for predicting the properties of undiscovered elements. Over time, the periodic table has evolved with advancements in atomic theory and experimental data. Modern periodic tables are based on the atomic number, which represents the number of protons in an element's nucleus, rather than atomic weight.
Nevertheless, Mendeleev's contributions to the development of the periodic table remain significant, and his original table served as the basis for subsequent refinements and advancements in our understanding of the elements.
Chemistry-phase II
1897-discovery of the electron as a sub-atomic particle by J J Thomson. Calculation of e/m value for electron.
Joseph John Thomson, often known as J.J. Thomson, was a prominent British physicist and Nobel laureate. He was born on December 18, 1856, in Cheetham Hill, Manchester, England, and passed away on August 30, 1940, in Cambridge, England.
Thomson is best known for his discovery of the electron and his work on the nature of cathode rays. In 1897, he conducted a series of experiments involving cathode ray tubes, which led him to propose the existence of negatively charged particles within atoms. He named these particles "corpuscles," which later came to be known as electrons.
Thomson's groundbreaking discovery of the electron revolutionized the understanding of atomic structure and laid the foundation for the development of modern atomic theory. His work provided evidence for the existence of subatomic particles and contributed significantly to the field of particle physics.
For his discovery of the electron, J.J. Thomson was awarded the Nobel Prize in Physics in 1906. He was also knighted in 1908 and became Sir Joseph John Thomson.
J.J. Thomson conducted experiments on cathode rays, which led to the determination of the charge-to-mass ratio (e/m) of electrons. In these experiments, he observed the deflection of cathode rays by electric and magnetic fields.
Thomson used a cathode ray tube, which is a sealed glass tube containing a low-pressure gas. The tube had two metal plates: an anode (positively charged) and a cathode (negatively charged). When a high voltage was applied across the plates, cathode rays were generated and emitted from the cathode. These rays were then accelerated towards the anode.
Thomson placed electric and magnetic fields perpendicular to each other and the direction of the cathode rays. By adjusting the strengths of these fields, he observed the extent of deflection of the cathode rays. Through careful measurements, he determined the relationship between the deflection, the electric field strength, the magnetic field strength, and the e/m value of the electrons.
Thomson's experiments showed that the deflection of cathode rays was dependent on the ratio of the electric field strength to the magnetic field strength. By varying the fields and measuring the deflection, he found that the e/m value for electrons was the same, regardless of the gas used in the cathode ray tube or the metal used for the electrodes. This suggested that the e/m value was a fundamental property of the electrons themselves.
Thomson's measurements led to the determination of the e/m value for electrons, which he found to be approximately 1.76 x 10^11 coulombs per kilogram (C/kg). This value provided important evidence for the existence of negatively charged particles within atoms and contributed significantly to the development of atomic theory.
1905- Millicon's oil drop experiment for calculation of charge and mass of an electron.
The Millican oil drop experiment, also known as the Millikan oil drop experiment, was a seminal experiment conducted by the American physicist Robert A. Millikan in 1909. The purpose of the experiment was to determine the charge of an electron and provide more precise measurements than J.J. Thomson's earlier work on the electron's charge-to-mass ratio (e/m).
In the experiment, Millikan observed tiny charged oil droplets suspended between two metal plates. He used a mist of oil droplets generated by an atomizer, which were allowed to fall through a small hole in the upper plate. By adjusting the electric field between the plates, Millikan was able to control the motion of the oil droplets.
As the oil droplets fell, some of them acquired an electric charge by picking up extra electrons from the surrounding air due to ionization. Millikan observed the motion of these charged droplets under the influence of gravity and the electric field.
By carefully measuring the rate at which the droplets fell and comparing it to their motion under different electric field strengths, Millikan was able to determine the charge on each droplet. He achieved this by finding the electric field strength required to balance the gravitational force acting on the droplet, causing it to remain suspended in mid-air.
By measuring the charge on many individual droplets and analyzing the data statistically, Millikan obtained a series of discrete values for the charge. He observed that the charges on the droplets were always multiples of a certain fundamental unit, which he deduced to be the charge of a single electron.
Through his precise measurements and calculations, Millikan determined the charge of an electron to be approximately 1.60 x 10^(-19) coulombs. This value was highly significant as it provided a direct measurement of the elementary charge, confirming the discrete nature of electric charge and supporting J.J. Thomson's earlier discoveries about the electron.
Millikan's oil drop experiment played a pivotal role in accurately determining the charge of an electron and further establishing the understanding of atomic structure and the quantized nature of electric charge. It contributed to the development of modern atomic theory and earned Robert A. Millikan the Nobel Prize in Physics in 1923.
Discovery of the existence of the atomic nucleus by Rutherford, using the scattering of alpha particles on a thin gold foil experiment.
The Rutherford gold foil experiment, conducted by the physicist Ernest Rutherford in 1910, was a landmark experiment that led to the discovery of the atomic nucleus and revolutionized the understanding of atomic structure. The experiment aimed to investigate the structure of atoms and the distribution of positive charge within them.
In the experiment, Rutherford and his team directed a beam of alpha particles (positively charged particles) at a thin gold foil. The alpha particles were emitted by a radioactive source and had high energy. Most of the alpha particles passed through the gold foil with little deflection, as Rutherford had expected based on the prevailing model of the atom at the time.
However, to their surprise, a small fraction of the alpha particles were significantly deflected at large angles and a few even bounced straight back. This result was unexpected because it contradicted the prevailing Thomson's "plum pudding" model of the atom, which suggested that the positive charge and electrons were uniformly distributed throughout the atom.
Rutherford interpreted these unexpected deflections as evidence that the atom has a tiny, dense, positively charged core at its center, which he called the "nucleus." He proposed that the majority of the atom's mass and positive charge were concentrated in this nucleus. The deflection of the alpha particles was attributed to their interaction with the positive charge of the nucleus.
This groundbreaking discovery led to the development of the Rutherford model of the atom, also known as the planetary model. According to this model, electrons revolve around the nucleus in specific orbits, similar to planets orbiting the Sun. The model laid the foundation for further advancements in atomic theory and contributed to the understanding of atomic structure.
The Rutherford gold foil experiment provided strong evidence for the existence of a dense, positively charged atomic nucleus and established the concept of the atom as a mostly empty space with a central nucleus. It played a crucial role in shaping our understanding of the atom and opened up avenues for further research into the nature of matter.
discovery of positively charged protons as part of the nucleus.
The discovery of protons in the atomic nucleus was a significant development in understanding the structure of the atom. It can be attributed to the work of several scientists, notably Ernest Rutherford and his colleagues.
In the early 20th century, Ernest Rutherford conducted a series of experiments, including the famous gold foil experiment mentioned earlier. Although the experiment led Rutherford to propose the existence of the atomic nucleus, it did not explicitly identify the nature of the particles within it.
The definitive discovery of protons came a few years later when Rutherford collaborated with Hans Geiger and Ernest Marsden on an experiment in 1909. In this experiment, they aimed a beam of alpha particles at a thin sheet of gold foil. They observed that some of the alpha particles were deflected at large angles, indicating the presence of a concentrated positive charge within the atom.
Based on these results, Rutherford proposed a model of the atom where a tiny, dense, positively charged nucleus existed at the center. To account for the observed deflections, he suggested that the positive charge was concentrated in a central core, while the electrons orbited around it.
In subsequent years, Rutherford continued his investigations, leading to the definitive identification of the positively charged particles within the nucleus as protons. In 1919, Rutherford collaborated with Thomas Royds, and together they conducted experiments involving the collision of alpha particles with various gases. Through their experiments, they observed that hydrogen nuclei (protons) were emitted during the collisions.
These findings demonstrated that the positively charged particles in the nucleus were indeed protons, which carry a charge equal in magnitude but opposite in sign to that of the electron. Rutherford's work provided strong evidence for the existence of protons as fundamental constituents of the atomic nucleus and contributed significantly to the development of the modern understanding of atomic structure.
It is worth noting that the discovery of neutrons, the other primary constituent of the atomic nucleus, came several years later, in 1932, through the experiments of James Chadwick. Chadwick's experiments demonstrated the presence of uncharged particles in the nucleus, which he identified as neutrons. This completed the picture of the atomic nucleus as a composite structure consisting of protons and neutrons.
Bohr's theory of hydrogen atom. quantized and discrete energy levels for an electron in an atom.
Niels Bohr's theory of the hydrogen atom, proposed in 1913, was a significant breakthrough in understanding atomic structure and laid the foundation for quantum mechanics. Bohr's theory introduced the concept of quantized energy levels for electrons and explained the stability of the hydrogen atom.
Bohr's theory incorporated elements of classical physics and newly emerging quantum ideas. Here are the key postulates of Bohr's theory:
- Electron Orbits: Bohr proposed that electrons revolve around the nucleus in specific, well-defined orbits or energy levels. Each orbit had a fixed energy associated with it.
- Quantized Energy: Electrons in Bohr's model could only occupy certain discrete energy levels and were prohibited from existing in between these levels. The energy levels were labeled by integer values (n = 1, 2, 3, ...) with the lowest energy level (n = 1) corresponding to the ground state.
- Emission and Absorption of Energy: Electrons could transition between energy levels by either emitting or absorbing energy in discrete packets called quanta. When an electron transitioned from a higher energy level to a lower one, it emitted a photon of energy corresponding to the energy difference between the two levels. Conversely, when energy was absorbed, the electron moved to a higher energy level.
- Stability and Radiation: According to Bohr's theory, electrons in stable orbits did not radiate energy and remained in their energy levels without spiraling into the nucleus. Only during transitions between energy levels, such as emission or absorption of photons, would energy be exchanged.
Bohr's theory successfully explained the discrete line spectra observed in hydrogen emission and absorption experiments. It also provided an explanation for why electrons did not continuously lose energy and collapse into the nucleus, as classical electromagnetism predicted.
concept of "atomic number", the number of positively charged protons in the nucleus of an atom.
The concept of atomic number is a fundamental concept in chemistry and atomic theory. It refers to the number of protons present in the nucleus of an atom. The atomic number uniquely identifies each element on the periodic table.
Here are a few key points about the concept of atomic number:
- Proton Count: The atomic number of an atom corresponds to the number of protons in its nucleus. Since protons carry a positive charge, the number of protons determines the atom's overall positive charge. In a neutral atom, the number of protons is balanced by an equal number of electrons.
- Element Identification: Each element on the periodic table is defined by its atomic number. For example, hydrogen has an atomic number of 1, indicating that it has one proton in its nucleus. Carbon has an atomic number of 6, meaning it has six protons, and so on. The atomic number distinguishes one element from another, allowing us to identify and classify elements.
- Periodic Table: The periodic table organizes elements based on their atomic numbers. Elements are arranged in order of increasing atomic number, from left to right and top to bottom. This arrangement helps identify patterns and trends in the properties of elements and facilitates the understanding of their chemical behavior.
- Isotopes: While the atomic number represents the number of protons, atoms of the same element can have different numbers of neutrons in their nucleus. These variations are called isotopes. Isotopes have the same atomic number but different mass numbers, which represent the total number of protons and neutrons in the nucleus.
- Chemical Properties: The atomic number plays a crucial role in determining the chemical properties of an element. The number of protons determines the element's identity and influences its reactivity, bonding behavior, and overall chemical behavior. Elements with different atomic numbers exhibit distinct chemical properties.
The concept of atomic number provides a systematic and organized way to identify and categorize elements based on their fundamental properties. It forms the foundation of the periodic table and is fundamental to understanding the structure and behavior of atoms and elements in chemistry and physics.
Plank's quantum theory, the energy propagation as quanta(pocket of energy).
Planck's quantum theory, developed by the German physicist Max Planck in 1900, marked a significant breakthrough in understanding the behavior of light and the concept of energy quantization. It laid the foundation for the development of quantum mechanics and revolutionized our understanding of the microscopic world. Here are the key points of Planck's quantum theory:
- Energy Quantization: Planck proposed that energy is quantized and can only exist in discrete packets or "quanta." Prior to Planck's theory, it was believed that energy could be emitted or absorbed in any amount, but Planck's idea suggested that energy exchange occurs in discrete, indivisible units.
- Planck's Constant: Planck introduced a fundamental constant, now known as Planck's constant (h), which relates the energy (E) of a quantum to its frequency (ν) through the equation E = hν. Planck's constant is a fundamental constant of nature and has a value of approximately 6.626 x 10^(-34) joule-seconds (J·s).
- Blackbody Radiation: Planck's quantum theory was initially developed to explain the phenomenon of blackbody radiation. Blackbody radiation refers to the emission and absorption of electromagnetic radiation by an idealized object (a blackbody) that absorbs all incident radiation. Planck introduced the concept that the energy of radiation is quantized in discrete units proportional to its frequency.
- Wave-Particle Duality: Planck's theory laid the groundwork for the wave-particle duality concept, which suggests that electromagnetic radiation exhibits both wave-like and particle-like properties. While Planck considered energy quanta as particles, later developments in quantum mechanics expanded this concept to include particles behaving as waves as well.
- Quantum Revolution: Planck's quantum theory played a crucial role in initiating the quantum revolution, which led to the development of quantum mechanics by subsequent physicists like Albert Einstein, Niels Bohr, Werner Heisenberg, and others. It fundamentally changed our understanding of the behavior of matter and energy at the microscopic level.
Planck's quantum theory opened up new avenues for research and provided a framework for understanding the discrete nature of energy and the behavior of particles and waves at the atomic and subatomic levels. It marked a pivotal moment in the history of physics and laid the groundwork for the development of quantum mechanics, which has since become one of the most successful and accurate theories in physics.
the photo-electric phenomenon and the idea of the photon, a massless particle.
Photoelectric emission, also known as the photoelectric effect, is a phenomenon where electrons are emitted from a material's surface when it is exposed to light or electromagnetic radiation of sufficient energy. The photoelectric effect played a crucial role in the development of quantum mechanics and provided strong evidence for the particle-like behavior of light.
Here are the key aspects of the photoelectric effect:
- Photon Absorption: When light interacts with matter, it behaves as particles called photons. Each photon carries a specific amount of energy that is determined by its frequency (or wavelength) according to the equation E = hν, where E is the energy, h is Planck's constant, and ν is the frequency of the light.
- Electron Ejection: In the photoelectric effect, when a photon with sufficient energy is incident on a material's surface, it can be absorbed by an electron in the material. If the absorbed energy is high enough to overcome the binding energy (work function) holding the electron in the material, the electron can be ejected from the material.
- Threshold Frequency: For a given material, there is a minimum frequency (threshold frequency) of light below which no photoemission occurs, regardless of the intensity of the light. The threshold frequency is directly related to the binding energy of electrons in the material.
- Electron Kinetic Energy: The kinetic energy of the emitted electrons depends on the energy of the incident photons and the binding energy of the electrons in the material. The kinetic energy can be determined by subtracting the work function (binding energy) from the energy of the incident photon.
- Experimental Observations: The photoelectric effect was extensively studied by Albert Einstein and others. Experimental observations showed that the number of emitted electrons increased with the intensity (brightness) of the incident light, but the kinetic energy of the emitted electrons was solely dependent on the frequency (energy) of the incident light.
The photoelectric effect posed a challenge to classical physics, which predicted that the intensity of light should determine the energy of emitted electrons. However, the observed results were in accordance with the quantum nature of light, where photons behave as discrete packets of energy. The photoelectric effect played a pivotal role in establishing the wave-particle duality of light and contributed significantly to the development of quantum theory.
dual nature of matter(electron), wave, and particle. d Broglie's relation between wavelength and momentum.
Louis de Broglie proposed the wave-particle duality of matter, suggesting that particles, such as electrons and other matter particles, could exhibit wave-like behavior. This idea was based on the notion that if light, which was known to have wave-like properties, could also exhibit particle-like behavior (as shown by the photoelectric effect), then particles might also possess wave-like characteristics.
De Broglie's key contribution was his mathematical relation that related the wavelength of a particle to its momentum. The de Broglie wavelength (λ) is given by the equation:
λ = h / p
Where λ is the wavelength, h is Planck's constant, and p is the momentum of the particle. This relation suggests that particles with higher momentum have shorter wavelengths, while particles with lower momentum have longer wavelengths.
De Broglie's hypothesis was confirmed experimentally in 1927 by Clinton Davisson and Lester Germer, who observed electron diffraction, demonstrating the wave-like behavior of electrons. Similar experiments were later conducted with other particles, such as neutrons and even larger molecules, further confirming the wave-particle duality of matter.
The de Broglie relation provided a bridge between classical mechanics and quantum mechanics, showing that particles could exhibit both particle-like and wave-like properties. It played a significant role in the development of quantum mechanics and contributed to our understanding of the behavior of particles at the microscopic level. The wave-particle duality concept is now a fundamental principle of quantum mechanics and has wide-ranging implications in various areas of physics.
Schrodinger's differential equation for the hydrogen atom and its solution. the inter-related quantum numbers n, l, and m for different energy orbitals of atoms. quantized energy levels.
Schrodinger's equation is a fundamental equation in quantum mechanics that describes the behavior of quantum systems, including particles and wave-like phenomena. It was formulated by the Austrian physicist Erwin Schrodinger in 1925.
The Schrodinger equation is a partial differential equation that relates the wave function (ψ) of a quantum system to its energy (E). The equation is given by:
Hψ = Eψ
Where H is the Hamiltonian operator, which represents the total energy of the system. The Hamiltonian operator incorporates terms related to the kinetic energy of the particles and the potential energy of the system.
The Schrodinger equation is a wave equation, and the wave function ψ represents the probability amplitude of finding a particle or a system in a particular state. The square of the wave function (|ψ|^2) gives the probability density of finding the particle at a specific position.
Solving the Schrodinger equation allows us to determine the allowed energy levels and corresponding wave functions for a quantum system. These energy levels represent the quantized states of the system, and the associated wave functions describe the spatial distribution of the system's particles.
The Schrodinger equation provides a mathematical framework for describing various phenomena in quantum mechanics, such as the behavior of electrons in atoms, the properties of molecules, and the behavior of subatomic particles. It allows for the calculation of energy spectra, particle interactions, and the time evolution of quantum systems.
The solutions to the Schrodinger equation have provided insights into many fundamental aspects of quantum mechanics, such as wave-particle duality, superposition, and quantum entanglement. The equation forms the basis for understanding the behavior of microscopic systems and is a cornerstone of modern physics.
The Schrödinger equation for the hydrogen atom describes the behavior of the electron in the hydrogen atom. It is a partial differential equation that relates the wave function of the electron to its energy. The equation is as follows:
Hψ = Eψ
In this equation, H is the Hamiltonian operator, which represents the total energy of the system, and ψ is the wave function of the electron, which depends on the coordinates of the electron in three dimensions (r, θ, φ) - representing radial distance, polar angle, and azimuthal angle, respectively. E represents the energy of the electron.
To solve the Schrödinger equation for the hydrogen atom, the wave function is typically separated into three independent functions that depend on the three coordinates: ψ(r, θ, φ) = R(r)Θ(θ)Φ(φ). This separation of variables allows us to break down the three-dimensional problem into three simpler one-dimensional problems.
The solutions to the Schrödinger equation result in a set of quantum numbers that characterize the energy and spatial distribution of the electron in the hydrogen atom. The principal quantum number (n) determines the energy level of the electron, with higher values of n corresponding to higher energy levels. The azimuthal quantum number (l) specifies the orbital angular momentum of the electron and determines the shape of the electron's orbital. The magnetic quantum number (m) indicates the orientation of the orbital in space.
The radial part of the wave function, R(r), is given by a combination of Laguerre polynomials and exponential functions, while the angular parts, Θ(θ) and Φ(φ), are described by spherical harmonics.
The solutions to the Schrödinger equation for the hydrogen atom provide a complete description of the energy levels and wave functions of the electron in the atom. They accurately predict the spectral lines observed in the hydrogen atom's emission and absorption spectra, as well as the spatial distribution of the electron in different orbitals.
The solutions also reveal the quantized nature of energy levels in the atom, with discrete energy values corresponding to different electron orbitals. The Schrödinger equation for the hydrogen atom and its solutions are essential in understanding atomic structure and have broader implications in quantum mechanics and the study of other atoms and molecules.
the valence electrons and valency for the property of elements.
The concept of valence electrons and valency is central to understanding the chemical properties and reactivity of elements. Valence electrons are the electrons in the outermost energy level, or valence shell, of an atom. These electrons play a crucial role in determining the element's chemical behavior, including its ability to form chemical bonds with other elements.
Here are the key points related to valence electrons and valency:
- Valence Electrons: Valence electrons are located in the highest energy level of an atom, also known as the valence shell. The number of valence electrons varies among elements. For the main group elements (Groups 1, 2, 13-18) in the periodic table, the number of valence electrons corresponds to the group number. For example, Group 1 elements, such as hydrogen and lithium, have one valence electron, while Group 14 elements, such as carbon and silicon, have four valence electrons.
- Chemical Reactivity: Valence electrons are involved in chemical reactions as they participate in the formation of chemical bonds. Atoms with incomplete valence shells tend to gain, lose, or share electrons to achieve a stable electron configuration, typically by obtaining a full valence shell of eight electrons (known as the octet rule). This process allows atoms to attain a lower energy state and increased stability.
- Valency: Valency refers to the combining capacity of an atom or the number of electrons an atom can gain, lose, or share to achieve a stable electron configuration. The valency of an element is often related to the number of valence electrons it possesses. Elements with one, two, or three valence electrons tend to lose those electrons to achieve a stable electron configuration and have a positive valency (1, 2, or 3, respectively). Elements with five, six, or seven valence electrons tend to gain electrons to complete their valence shells and have a negative valency (-3, -2, or -1, respectively).
- Bonding and Stability: Valence electrons are involved in the formation of chemical bonds, such as ionic bonds, covalent bonds, and metallic bonds. Elements with similar valence electron configurations often exhibit similar chemical properties and tend to form similar types of compounds. For example, elements with one valence electron, like the alkali metals (Group 1), readily lose that electron to form positively charged ions (cations) and are highly reactive.
Understanding the concept of valence electrons and valency provides insights into how elements interact and form compounds. It helps predict the types of chemical bonds that elements can form and their chemical reactivity. The arrangement of valence electrons ultimately determines the element's position in the periodic table and its role in various chemical reactions and compounds.
Covalent bonds and ionic bonds for chemical compound formation.
