Chemistry for Beginers

This universe is made up of matter and energy.Matter is made of elements and compounds.

The element was defined by Robert Boyle in 1661 while working in Royal society England.He distinguished chemistry from alchemy.The elements like gold, silver copper iron were already known since long. By the year 1777- some new elements were discovered and named as, Hydrogen , Oxygen Carbon, Sulphur and so on.

In 18^th century,The chemists like Black, Cavendish, Priestley, Shelley and Lavoisier worked as builders of chemistry.A List of chemical elements was made by Lavoisier for the first time.He was a french chemist. He gave the law of conservation of mass [in a chemical change].The phlogiston theory was disproved by Lavoisier and the process of burning was explained with clear experimental evidence by him. He gave the oxygen theory of combustion. By 1784- hydrogen was burnt in a jar containing oxygen, to produce water by Cavendish an English chemist. Thus water was confirmed as a compound[not as element]. In 1800,- water was decomposed by applying external electricity into two gases, oxygen and hydrogen. Thus elemental nature of matter was established.

1803- behavior of water as air, liquid and solid was studied and absorption of air by liquid water led to the particle nature of matter.

Thus the atomic[particle] nature evolved and Dalton gave the atomic theory of elements and matter.

“All elements are made up of very minute small particles called atoms. These atoms cannot be created or destroyed” said Dalton. All atoms of an element are same in size and mass.

Atoms of different elements have different relative atomic weights. The weight of hydrogen was taken as unit mass. Therefore each element was distinguished by its atomic weight. Dalton made a list of atomic weights of hydrogen, oxygen, carbon, nitrogen etc.

1812- new elements were discovered and named by Davy [Na,K,Mg, Ca, Cl etc].

1814- Berzelius wrote the elements using symbols. He gave unique symbol to each element.It was confirmed that mass is conserved and simply atoms re-arrange in a chemical change. Thus when hydrogen burns in oxygen, the atoms re-arrange as H2O molecules. This could be written as

H2 + O2 = H2O . In this notation the total atoms are not balanced. The balanced form is written as 2H2 + O2 = 2H2O. This became a powerful tool to study the chemical science.

The new elements were discovered and named. The first world chemical conference was called during 1860 in Germany by Kekule. It was the first meet of its kind where 140 delegates from all over the Europe participated. At the conclusion session,It was decided to apply the molecular nature of gases to determine atomic weights of different elements. By this time more than 60 elements were know. Berzelius named all atoms with unique symbols. All the participants agreed for Berzelius symbols for writing the elements and atoms. Thus chemistry took a defining shape as pure science.

The Russian young scientist Mendeleev, arranged the elements in increasing order of their atomic weights and found the repeated nature of properties after a period of seven elements. Thus he constructed the first periodic table of elements during 1869. In his table of elements he gave gaps for elements not yet discovered. He could explain the properties of those unknown elements in advance. When they were discovered they exactly fit in the table. Thus periodic table was taken seriously by chemists all over the world.

Note that all this story happened before the knowledge of electron, since electron was discovered at the end of the century in 1897 or so. By this time the noble gases were discovered and all of them fitted properly in column eight of Mendeleev's periodic table. The universal law of periodic property of elements was held. The modern periodic table has eighteen columns and seven rows.

After discovery of electron as sub-atomic particle, modern chemistry took a new turn. The quantum theory was applied to Hydrogen atom in order to explain discrete energy levels of hydrogen atom by Bohr in 1913. The existence of nucleus, and protons, neutrons as sub-nucleic particles was confirmed. Atom was defined by its atomic number instead of atomic mass number. Number of protons in an atom was called its atomic number. All elements were identified by their atomic numbers. Atoms with same atomic number and different mass number were called isotopes. C12, C13, C14 are isotopes of element carbon. The mean mass of all isotopes of an element, is taken as mass number for an element. Therefore mass number is a fractional value[not a whole number].

Chemistry is the study of elements listed in the modern periodic table.