Four Pairs of Electrons

Carbon is in group 4 so methane CH₄ has four C-H bonds. The four electron pairs repel each other into a tetrahedral arrangement so they are as far apart as possible in three-dimensional space. The bond angle is 109.5°Any central atom with four bonding pairs and no lone pairs is tetrahedral with bond angles of 109.5°. Examples are the ammonium ion NH₄⁺ and NCl₄⁺.A lone pair repels more strongly than a bonding pair. When one of the four electron pairs is a lone pair, as in ammonia NH₃ or NCl₃, the three bonding pairs are pushed slightly closer together. The shape is trigonal pyramidal and the bond angle is about 107°.When two of the four pairs are lone pairs, as in water H₂O, the shape is bent (non-linear) and the bond angle is about 104.5°.In all three cases the four electron pairs are arranged tetrahedrally. The name of the shape describes only the positions of the atoms, so lone pairs are not counted when naming it.