Some of the most essential facts on Atomic Structure and Chemical Bonding are :

1. Elements are made up of atoms.

2. Each atom has a nucleus situated at the center. It contains positively charged particles called protons, and neutral particles called neutrons.

3. Electrons are negatively charged particles which move around the nucleus in definite circular paths called orbits, shells or energy levels.


4. The mass number of an element is equal t the sum of the number of protons and number of neutrons in its nucleus.

5. Number of protons equals the number of electrons in an atom; therefore, an atom is electrically neutral.

6. Atomic number is the number of protons of an atom.

7. Isotopes are atoms of the same element having different mass numbers.


8. The distribution of electrons in various shells or energy levels in an atom is called the electronic configuration of that atom.

9. According to Bohr and Bury, the maximum number of electrons that can be accommodated in any energy level of an atom is given by the formula 2n2, where ‘n’ represents the number of the energy level.

10. In order to exist independently by itself an atom must have eight electrons in its outermost shell two electrons if there is only one shell. This is the octet rule.

11. Atoms try to attain stable configuration (completing their outermost shell) either by losing, gaining or sharing electrons.


12. The force of attraction that holds atoms together in a molecule is known as a chemical bond.

13. A bond between an anion and cation is called an ionic bond. Cations give electrons to the anions.

14. A covalent bond id a bond in which both the reacting atoms are short of electrons. Thus, they attain stable electronic configuration by sharing electrons.

15. Coordinate bond is a covalent bond in which the shared pair of electrons is contributed by only one of the two atoms.