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.
