4.1) If two bond pairs are present in two covalent bonds around the nucleus of the central atom without any lone pairs in the valence shell, they must be separated by 1800 to have minimum repulsion between them. Thus, the molecule would be linear.

Example:

4.2) If three bond pairs are there in three covalent bonds around the nucleus of the central atom, without any lone pairs they get separated by 120° along three corners of a triangle. Therefore, the shape of the molecule is trigonal-planar.

Example:

NOTE:

Did you notice that in BeCl 2 and BF3 the central atoms Be and B did not possess 8 electrons around them in the valence shell. They have only 4 and 6 electrons respectively. These molecules are known as electron deficient molecules.
4.3) If there are four bond pairs in the valence shell of the central atom, the four bond pairs will orient along the four corners of a tetrahedron (three dimensional arrangement) and the bond angle expected is 1090 28'
.

Example: Methane.