Category: Class 9

Dalton atom theory

Keeping in the view of chemical combination and the work of British chemist john Dalton Provided the basic theory about nature of matter known as Dalton’ s atomic theory. The basic postulate of Dalton’s atomic theory are following. Postulate: All matter is made up of tiny particles called atom which participated in chemical reactions. For […]

Law of constant proportion

The law was proposed by a French chemist joseph L. Proust. In 1797 and hence it also referred to proust’s law. Law State: In a chemical substance elements are always in fixed proportion by mass. “ A chemical compounds always found to be made up of same elements chemically combine togetherin the same fixed proportion […]

Chemical Formula

The combining capacity of elements or atom is known as valency, and valency can be used to find out how the atom of elements Will combine with atom of another elements to form a chemical compounds. Chemical formula is showing all constituents of chemical compounds by chemical symbol in a fixed proportion or according to […]


The capacity of an atom to give , accept or share electrons to achieve there octet state. OR The number of electrons gain, lost, or share by the atom of elements so as to complete is octet (or duplet in case elements having only K shell) is called valency of elements. Here comes the concept […]


“An atom or group of atom which carries  a positively charge and negatively charge is called ion.” Every atoms contain equal number of electrons (negatively charged) and protons ( positively charged) .  Both charges balance each other, hence atom is electrically neutral. Cation (+) : The ion carries positively charge called cation. A cation bears […]

Molecular Mass

Molecular mass of substance (elements or compound) is the relative mass of its molecule Compared with that of an atom Of carbon-12 isotope taken as 12. In other word molecular mass of substance represent the number of times the molecule of that substance is heavier than 1/12 of  the mass of an atom of C-12 […]


“Molecule is an electrically neutral group of two or more atom chemically bonded together by means of attractive force.” OR “A molecules is group of two or more atom which are held together strongly  by some kind of attractive forces.” Such an attractive force holding the atoms together is called chemical bond. A molecules is […]

Elements and symbol

A symbol is the shorthand notion of the elements which can be represented by a sketch or letters etc. Dalton was the first to used symbols to represent elements in short way but Dalton symbols for elements were difficult to draw and inconvenient to use them So Dalton’s symbols  are only for historical importance. They […]

Atomic Mass

Mass of one atom of an elements called atomic mass.  OR The total number of protons and neutron in an atom. OR Atomic mass Of an elements may be defined as the average relative mass of  an atom of the elements  as compared With mass Of an atom of carbon.       OR The atomic mass is […]


Atom Around 500 BC ago Indian philosopher experiments on rice , he called it Padarth they break rice into very small tiny particles until they don’t break it then they give them name of Parmanu. During that time Greeks Philosopher Democritus, and Leucippus also work on this. “All matter is composed of small indivisible particles […]