Characteristic shapes and bond angles within covalent molecules

Inside a covalent molecule, the covalent bonds are directed in space at specific angles. In the case of the methane molecule the carbon–hydrogen bonds are at 109.5 , in other words towards the corners of a tetrahedron with the carbon atom at its centre.
All covalent bonds have their own characteristic bond angles. These influence the shape of any covalent molecule. The molecules can freely twist about any single bonds, e.g. C C; H H; C H, O H, but not about any double bonds, e.g. C O or C C.

More complicated molecules twist and bend to make sure that all the atoms take up positions that allow them maximum free space and non-interference with each other. The very complicated DNA molecules with hundreds of atoms in them twist in a characteristic spiral manner (Figure 2.10). The characteristic shape of each molecule influences its effect on how it behaves in our body and within cells.