G11Chem

6.Atomic number
The number of protons in the nucleus or
an atom of an element is known as the atomic number of that element.

1. Mass number

The mass number of an element is the sum

of the number of protons and neutrons in the nucleus of an atom of that element.

1. Isotopes
   Atoms of the same element with different masses are called isotopes.
2. Electropositive elements
   _Metals are electropositive elements. They tend to lose electrons and form positive ions.
3. Electronegative elements

Non-metals are electronegative elements. They tend to gain electrons and form negative ions.