• Can you explain the reasons for all these?

Ionic bond is formed between atoms of elements with electronegativity difference equal to or greater than 1.9.

In ionic bond formation, you have noticed that atoms either lose electrons or gain electrons to attain octet in valence shell. i.e., in an ionic bond, transfer of electrons takes place between combining atoms.

The tendency of losing electrons to form cations (or) gaining electron to form anions depends on the following factors:

i. Atomic size

ii. Ionisation potential

iii. Electron affinity

iv. Electronegativity

The atoms of elements with low ionisation energy, low electron affinity high atomic size and low electronegativity form cations.

The atoms of elements with high ionisation potential, high electron affinity, small atomic size and high electronegativity from anions

B.Cavalent bond

G.N. Lewis (1916) proposed that atoms of some elements could achieve an octet in their valence shells without transfer of electrons between them. They can attain octet configuration in their valence shells by sharing the valence electrons with one or more atoms.

The electrons shared between two atoms belong to both the atoms and the sharing of electrons between them leads to the formation of a chemical bond known as covalent bond.

For example, take two fluorine atoms which form a stable molecule. Each fluorine atom contributes one electron for bonding and the electron pair that is formed in this way is mutually shared by both the fluorine atoms. Each atom in the F2 molecule has an octet of valence electrons.