The angle between the carbon atoms in diamond is 109.Why?

Each carbon atom in a diamond is covalently bonded to four other carbons in atetrahedron. These tetrahedrons together form a 3-dimensional network of six-membered carbon rings (similar tocyclohexane), in thechair conformation, allowing for zerobond anglestrain. This stable network ofcovalent bondsand hexagonal rings, is the reason that diamond is so strong.