Elements of chemistry

1661-Robert Boyle defined element.

1778-Lavoisier named Oxygen and Hydrogen as elements. He gave the law of conservation of mass. He produced a list of 23 elements for the first time.

1781-Cavendish synthesized water by burning Hydrogen in Oxygen. Earlier people thought that water was an element;but it was established that water is made up of two colorless gases oxygen and hydrogen.

1800-Volta invented the battery called voltaic pile, which became a source of electricity.

1803-Dalton gave the atomic theory of elements; prepared a list of atomic weights of hydrogen , oxygen, carbon, nitrogen,sulphur and phosphorus.

1811-Avogadro gave the concept of molecules for gases. He hypothesized that equal volumes of all gases contain same number of particles [at same temperature and pressure]

1812-Humphry Davy used the voltaic pile to isolate new elements like potassium, sodium, magnesium, calcium, barium strontium etc.

1817-Berzelius named the elements and represented them by symbolic notations. He used symbols to write chemical formulae for reactions. He determined atomic weights of different elements.

1834- Michael Faraday gave the laws of electrolysis.

An electrolytic cell is an electrochemical cell that drives a non-spontaneous redox reaction through the application of electrical energy. They are often used to decompose chemical compounds, in a process called electrolysis. An electrolytic cell has three component parts: an electrolyte and two electrodes (a cathode and an anode). The electrolyte is usually a solution of water or other solvents in which ions are dissolved.

Faraday's law stating that “the amount of any substance deposited or liberated during electrolysis is proportional to the quantity of electric charge passed and to the equivalent weight of the substance.”

Faraday’s second law of electrolysis states that, when the same quantity of electricity is passed through several electrolytes, the mass of the substances deposited are proportional to their respective chemical equivalent or equivalent weight.

Chemical Equivalent or Equivalent Weight

The chemical equivalent or equivalent weight of a substance can be determined by Faraday’s laws of electrolysis, and it is defined as the weight of that subtenancy which will combine with or displace the unit weight of hydrogen.

The chemical equivalent of hydrogen is, thus, unity. Since valency of a substance is equal to the number of hydrogen atoms, which it can replace or with which it can combine,

The chemical equivalent of a substance, therefore may be defined as the ratio of its atomic weight to its valency.

Equivalent weight = Atomic weight/Valency