Chemistry (NTSE/Olympiad)  

2. Elementary Idea of Bonding

Single covalent bond

Single covalent bond :
A single covalent bond is formed when one pair of electrons is shared between two atoms.
1. Formation of a hydrogen molecule (H2) :

A molecule of hydrogen consists of two hydrogen atoms. Each hydrogen atom has one electron. When two atoms of hydrogen combine, one electron of each takes part in sharing. Thus, two electrons (one pair of electrons) are shared between the two atoms.

The shared electron pair always exists between the two atoms. The two dots between the two H atoms represent the pair of shared electrons. One pair of shared electrons gives a single bond. Such a bond is represented by a short line between the two atoms. Thus, a hydrogen molecule may be represented as in figure.

Once the bond is formed, the both atoms have a stable configuration of the noble gas helium.
2. Formation of a methane molecule (CH4): A carbon atom has four electrons in its outermost shell (valence shell). It shares its valence electrons with those of four H atoms. Thus, an atom of carbon forms four single covalent bonds with four H atoms.

14. Pictorially, a methane molecule may be represented as in Figure.

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