CHEMISTRY [2 Mark Question Answer]

Every atom has proton, neutron and electron. Proton has positive charge, electron has negative charge and neutrons have no charge. In every stable atoms, number of electrons and protons are same. So every stable atoms have zero electrical charge.
Lets take an example of sodium atom which has 11 protons and 11 electrons so it is electrically stable means there is no charge on sodium atom. But know that sodium has 1 free electron in its outer layer and if we remove this electron than sodium atom will have positive charge.

(a) bound electrons - As nucleus is positively charged it strongly attracts the negative charged electrons. The electron orbit close to the nucleus are tightly bound by strong attractive force of nucleus. These electrons are known as bound electrons.
(b) valence electrons Valence is the number of electrons an atom must lose or gain to attain the nearest noble gas or inert gas electronic configuration. "Electrons in the outer shells that are not filled are called valence electrons".

(a) atomic number - The atomic number of an element is determined by the number of protons in it, and it is used to differentiate one element from another. The mass number of an element is determined by the number of protons and neutrons combined.
(b) mass number - mass number, in nuclear physics, the sum of the numbers of protons and neutrons present in the nucleus of an atom.