Question

How do valence electrons affect chemical bonding?

Answer 1

We need to know what are valence electrons and its importance in chemical bonding.Valence electrons are electrons present in the outermost shell of an atom. Atoms lose or gain these valence electrons which leads to chemical bonding. Also, the attractive force which holds various constituents such as atoms and ions together in different chemical species is called a chemical bond. To explain how valence electrons affect chemical bonding, we shall consider covalent bonding between atoms.

Complete step by step answer:
We must remember that a covalent bond is a chemical bond that is formed by the sharing of electron pairs between atoms. A strict rule is followed by atoms during covalent bonding which is the octet rule. According to this rule, main group elements tend to bond in such a way, either by losing, gaining or sharing electrons such that each atom has 8 electrons in its outermost (valence shell). This craving of elements to satisfy its octet is the main reason for the chemical bonding. When two atoms share one electron pair, they are said to be bonded by a single covalent bond. For example, $C{l_{2}}$ molecule. $Cl$ has $7$ electrons in its valence shell with the electronic configuration $\left[ {Ne} \right]3{s^2}3{p^5}$ .To complete its octet, it requires one electron. In a similar way, the double bond in an oxygen molecule can be explained by understanding the covalent bonding between the oxygen atoms. $O$ has the electronic configuration $\left[ {He} \right]2{s^2}2{p^4}$ . To complete its octet, it requires two electrons hence two oxygen atoms are bonded by a double bond.
In addition, the reactivity or the inertness of an atom is also determined by the valence electrons of that atom. Elements of Group 1 and 2 of the periodic table are highly reactive since they need only 1 and 2 electrons respectively to complete their octet. Similarly, elements of group 18 which have a satisfied octet are not reactive hence inert. Non-metals such as halogens are also extremely reactive since they are highly electronegative.
Hence, it is clear that the roots of chemical bonding are valence electrons and their main objective is to form a group of 8 valence electrons.

Note:
It must be noted that the valence electrons can be determined by writing the electronic configuration of the element. Also, I n some compounds such as $LiCl$, $Be{H_2}$ , $AlC{l_3}$ ,etc, the number of electrons surrounding the central atom (whose valence electrons are less than four) is less than eight after the bonding. Also, in molecules with an odd number of electrons like $NO$ and$N{O_2}$ , the octet rule is not satisfied for all the atoms. Furthermore, in some compounds such as PF5, there are more than eight valence electrons around the central atom (expanded octet).