Chapter 4: Unit 9. Formation of Covalent Compound
Formation of Covalent Compound
A covalent bond is formed when a valence electron pair is shared between two atoms with a very low difference in electronegativity. As mentioned before, most covalent bonds are formed between two nonmetals or between a nonmetal and a metalloid. When electrons are shared, both atoms gain stability by achieving octet. The shared electron pair is called a bond and the electron pairs involved in creating the bond is called bonding electrons. Other valence electrons that don’t participate in bond formation are called lone pair of electrons.
There are some exception to the octet rule, Hydrogen follows duet rule. It is happy with wo electrons. The number of covalent bond possible in a homonuclear diatomic molecule is always 8-valence electrons.If two or three electron pairs are shared, there are called double and triple bonds respectively.
A single bond is represented by a line “_” and a double bond is represented by double line “=”. A lone pair of electrons is indicated by two dots. “..” on the atom.
The following diagram represents potential energy diagram of H2 molecule formation. Although two isolated nonmetals are electrically neutral, ideally they don’t experience any opposite charge attraction. But when the two atoms of same or different nonmetals are brought close together, due to their momentary displacements of protons and electrons, gradually when they reach an optimum distance the covalent single bond is formed. The internuclear distance between two bonded atoms can be determined experimentally and called bond length.
The overlap of above two electrons in H2 molecule created a single bond. Both H atoms share this pair of electrons.
In the example below, to achieve octet, oxygen molecule must form double bond. Therefore, 4 bonding electrons and 8 lone pair of electrons are present in O2 molecule.
Below are some examples of covalent molecules with bonding and nonbonding(lone pair) electrons.
The following video may be helpful in understanding covalent bonding.
Questions
- How many covalent bonds are possible for Carbon?
- How many lone pair and bond pairs of electrons present in N2 molecule?
Ans:1. 4 2. Bond pair: 3, lone pair: 2