Define Following Terms Atom

Define the following terms : 1. Atom 2. Molecule 3. Radicals 4. Valency

Answers:

1. Atom : An atom is the smallest indivisible unit of an
   OR
   Atom is the smallest unit of matter.
2. Molecule : Molecule is the smallest unit of a compound (or an element) which always has an independent existence.
3. Radicals : A radical is an atom of an element or a group of atoms of different elements that behaves as a single unit with a positive or negative charge on it.
4. Valency : It is the number of electrons donated or accepted by the valence shell of an atom during chemical combination.
5. Periodic table represents the tabular arrangment of elements in horizontal rows called periods and vertical columns called groups in order to classify the elements and their systematic study.