Science before 1900: and Science after 1900:

Science before 1900: and Science after 1900:

13th century -New Universities were established in many parts of Europe.

16th century, sea adventure started from Europe to discover new places along the sea coasts.

17th century, Royal Society of London and The French Academy of sciences were founded to study the pure and applied Science.

18th century, scientists discovered the gases,like CO2, H2, O2 and Lavoisier of France correctly interpretation the process of burning,he explained the combustion theory. He also made a list of Known elements for the first time. He explained the concept of oxidation and reduction. He gave the law of conservation of mass.

Antoine Lavoisier revolutionized chemistry. He named the elements carbon, hydrogen and oxygen; discovered oxygen’s role in combustion and respiration; established that water is a compound of hydrogen and oxygen; discovered that sulfur is an element, and helped continue the transformation of chemistry from a qualitative science into a quantitative one.

In 1772 Lavoisier discovered that when phosphorus or sulfur are burned in air the products are acidic. The products also weigh more than the original phosphorus or sulfur, suggesting the elements combine with something in the air to produce acids. But what?

In 1779 Lavoisier coined the name oxygen for the element released by mercury oxide. He found oxygen made up 20 percent of air and was vital for combustion and respiration. He also concluded that when phosphorus or sulfur are burned in air, the products are formed by the reaction of these elements with oxygen.

In 1777 Lavoisier correctly identified sulfur as an element. He had carried out extensive experiments involving this substance and observed that it could not be broken down into any simpler substances.

In 1778 Lavoisier found that when mercury oxide is heated its weight decreases. The oxygen gas it releases has exactly the same weight as the weight lost by the mercury oxide.

Lavoisier announced a new fundamental law of nature: the law of conservation of mass:

• matter is conserved in chemical reactions

In 1783 Lavoisier coined the name ‘hydrogen’ for the gas which Henry Cavendish had recognized as a new element in 1766; Cavendish had called the gas inflammable air.

Lavoisier burned hydrogen with oxygen and found that water was produced, establishing that water is not an element, but is actually a compound made from the elements hydrogen and oxygen. 

In 1789 Lavoisier published his groundbreaking Elementary Treatise on Chemistry. Itcontained a list of chemical elements. The list included oxygen, nitrogen, hydrogen, sulfur, phosphorus, carbon, antimony, cobalt, copper, gold, iron, manganese, molybdenum, nickel, platinum, silver, tin, tungsten, and zinc.

Antoine Lavoisier was called the father of modern chemistry.

19th century, the concept of atom was put forth by John Dalton and he calculated the relative atomic weights of diferent elements, he compared the atomic masses, taking hydrogen atom as a unit mass.

Dalton's fascination with gases gradually led him to formally assert that every form of matter (whether solid, liquid or gas) was also made up of small individual particles. In an article he wrote for the Manchester Literary and Philosophical Society in 1803, Dalton created the first chart of atomic weights.

In 1808,In A New System of Chemical Philosophy, Dalton introduced his belief that atoms of different elements could be universally distinguished based on their varying atomic weights. In so doing, he became the first scientist to explain the behavior of atoms in terms of the measurement of weight. He also uncovered the fact that atoms couldn't be created or destroyed.

The law of definite proportion and multiple proportion was explained, relating to a chemical change.

Elements were represented by symbols and chemical reactions were written using these symbols.

Volta developed a primary battery cell by compiling a pile of dissimilar elements arranged alternately with moist cardboard separators. He could produce steady electricity. The cell was further modified by Denial for practical use.

Alessandro Volta Invented the first electric battery – which people then called the “voltaic pile” – in 1800. Using his invention, scientists were able to produce steady flows of electric current for the first time, unleashing a wave of new discoveries and technologies.

The water was decomposed using the electric energy into two gases. Water was confirmed as a compound.

Using large battery, Davy isolated new elements like K, Na Ca etc.

Davy discovered several new elements. In 1807 he electrolyzed slightly damp fused potash and then soda—substances that had previously resisted decomposition and hence were thought by some to be elements—and isolated potassium and sodium. He went on to analyze the alkaline earths, isolating magnesium, calcium, strontium, and barium.

The list of elements grew considerably.

In the year 1860, A first chemical meet was held in Germany, where 140 delegates participated to discuss the principles of chemistry.

The very first international scientific conference was held in Karlsruhe, Germany on Sept. 3, 1860.
 It was an science landmark also, essential for clearing up several major difficult problems that were blocking the advance of chemistry.
Clearing up the element sequence (using weights at that time) took place by Cannizzaro's interpretation of Avogadro's Law.

German chemist Lothar Meyer, and the Russian chemist Dmitri Mendeleev, who had both been in attendance at Karlsruhe, constructed element arrangements using the Cannizzaro numbers - on tables: with the elements arranged in rows and columns - for schoolbooks.

An important long-term result of the Karlsruhe Congress was the adoption of the now-familiar atomic weights (actually, atomic masses) of approximately 1 for hydrogen, 12 for carbon, 16 for oxygen, Cl 35.5, K39, Ca 40, Br 80, Rb 85, Sr 88, I 127, Cs 133, Ba 137 and so forth. There was also a recognition that certain elements, such as hydrogen, nitrogen, and oxygen, were composed of diatomic molecules and not individual atoms.

In 1869 Mendeleev arranged the known elements in a table of rows and columns known as periodic table of elements.

On March 6, 1869, Mendeleev made a formal presentation to the Russian Chemical Society, entitled The Dependence between the Properties of the Atomic Weights of the Elements, which described elements according to both weight and valence. This presentation stated that

1. The atomic mass, exhibit an apparent periodicity of properties.
2. Elements which are similar as regards to their chemical properties have atomic weights which are either of nearly the same value (e.g., Pt, Ir, Os) or which increase regularly (e.g., K, Rb, Cs).
3. The arrangement of the elements in groups of elements in the order of their atomic weights corresponds to their so-called valencies, as well as, to some extent, to their distinctive chemical properties; as is apparent among other series in that of Li, Be, B, C, N, O, and F.
4. The elements which are the most widely diffused have small atomic weights.
5. The magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body.
6. We must expect the discovery of many yet unknown elements–for example, two elements, analogous to aluminium and silicon, whose atomic weights would be between 65 and 75.
7. The atomic weight of an element may sometimes be amended by a knowledge of those of its contiguous elements. Thus the atomic weight of iodine (126.9).
8. Certain characteristic properties of elements can be foretold from their atomic weights.

Mendeleev studied petroleum origin and concluded that hydrocarbons are abiogenic and form deep within the earth. He wrote: "The capital fact to note is that petroleum was born in the depths of the earth, and it is only there that we must seek its origin."

By the end of the century almost all elements were known.

The 20th century opened with alternating electric current. Alternating current (AC) has the distinct advantage over direct current (DC; a steady flow of electric charge in one direction) of being able to transmit power over large distances without great loss of energy to resistance.

Alternating current systems can use transformers to change voltage from low to high level and back, allowing generation and consumption at low voltages but transmission, possibly over great distances, at high voltage, with savings in the cost of conductors and energy losses. The AC power systems was developed and adopted rapidly after 1886 due to its ability to distribute electricity efficiently over long distances, overcoming the limitations of the direct current system.

For three-phase at utilization voltages, a four-wire system is often used. When stepping down three-phase, a transformer with a Delta (3-wire) primary and a Star (4-wire, center-earthed) secondary is often used so there is no need for a neutral on the supply side.

Electron was discovered as a subatomic particle. 

 Subatomic particles:

Electron was discovered as a subatomic particle.

 Properties of cathode ray particle

1. They travel in straight lines.

2. They are independent of the material composition of the cathode.

3. Applying electric field in the path of cathode ray deflects the ray towards positively charged plate. Hence cathode ray consists of negatively charged particles.

J. J. Thomson measured the charge-by-mass-ratio (e/m) of cathode ray particle using deflection in both electric and magnetic field. E/m = −1.76×10⁸ coulomb per gram

The cathode ray particle turned out to be 2000 times lighter than hydrogen.

In 1909, American physicist R. Millikan measured the charge of an electron using negatively charged oil droplets. The measured charge (e) of an electron is −1.60×10⁻¹⁹ Coulombs.

Using the measured charge of electron, we can calculate the mass of electron from e/m ratio given by J. J. Thomson’s cathode ray experiment.

e/m = −1.76×10⁸ Coulomb-per-gram, m = e/−1.76×108, Putting e = −1.60×10⁻¹⁹ Coulomb,

  m = 9.1×10⁻²⁸ gram.

 What we have learned

1. Electron was discovered by J. J. Thomson in Cathode Ray Tube (CRT) experiment.

2. Electrons are negatively charged particles with charge-to-mass ratio −1.76×10⁸ C/gm

3. The charge of an electron was measured by R. Millikan in Oil drop experiment.

4. Charge of an electron is −1.60×10⁻¹⁹ C

5. Mass of an electron is 9.1×10⁻²⁸ gram.

6. Electron is approximately 2000 times lighter than hydrogen.

Within the next three decades the structure of atom was completely known.

Rutherford proposed the following structural features of an atom:

1.Most of the atom’s mass and its entire positive charge are confined in a small core, called nucleus. The positively charged particle is called proton.

2.Most of the volume of an atom is empty space.

3.The number of negatively charged electrons dispersed outside the nucleus is same as number of positively charge in the nucleus. It explains the overall electrical neutrality of an atom.

But scientists soon realized that the atomic model offered by Rutherford is not complete. Various experiments showed that mass of the nucleus is approximately twice than the number of proton. What is the origin of this additional mass?

In 1930, W. Bothe and H. Becker found an electrically neutral radiation when they bombarded beryllium with alpha particle. They thought it was photons with high energy (gamma rays).

 In 1932, Irène and Frédéric Joliot-Curie showed that this ray can eject protons when it hits paraffin or H-containing compounds.

 The question arose that how mass less photon could eject protons which are 1836 times heavier than electrons. So the ejected rays in bombardment of beryllium with alpha particles cannot be photon.

 In 1932, James Chadwick performed the same experiment as Irène and Frédéric Joliot-Curie but he used many different target of bombardment besides paraffin. By analyzing the energies of different targets after bombardment he discovered the existence of a new particle which is charge less and has similar mass to proton. This particle is called neutron. Beryllium undergoes the following reaction when it is bombarded with alpha particle: Be⁹ + ᾳ⁴ → C¹² + C¹³ + ꞑ

 By this time, man could fly in the air, transport large quantities of goods seamlessly on railroads. Can instantly talk on the phone and broadcast on radio, can make cinemas and all. Men fought two world wars. They could split the atom to produce bombs and one suck atomic bomb was used against Japan by the USA in world war-II. This led to the end of wars once and for all. After world war-II, Most of the colonies have become free nations.