A carbon atom has four electrons in its outermost valence shell. So, it needs four more electrons to complete its octet. A carbon atom completes its octet only by sharing its valence electrons with other atoms. As a result, carbon atom forms four covalent bonds by sharing valence electrons with other atoms. This is known as tetravalency of carbon,(tetra means four). These four valences of carbon are directed towards four corners of a tetrahedron, and inclined to each other atomic an angle of a 109° 28´.
The carbon atom is assumed to be atomic the center of the tetrahedron. In common use, the four valences of carbon are shown by four bonds around a carbon atom as shown alongside.