Question

why do atoms aproach each other?

Answer 1

According to Kossel-Lewis aaproach, atoms combine to complete their octets(8 electrons in the outermost shell) or duplet(2 electron in outermost shell) in case of H, Li, Be to attain nearest noble gas configuration. This can occur in 2 ways:

1. By complete transference of electrons from one atom to another forming ionic bond.

2. By sharing of electons:

a. When the shared electrons are contributed by two combining atoms equally, bond formed is covalent.

b. When these electrons are contributed entirely by one of the atoms but shared by both, bond formed is coordinate or dative bond.

This combination of atoms can also be explained on the basis of electronegativity difference, when the electronegativity difference is larger, bond formed is ionic and when electronegativity difference is less, bond formed is covalent. Covalent bond can be again of two types-polar( electronegativity difference is there) and non-polar( electronegativity difference is neglible)