Why is the basic shape of alkanes tetrahedral?

1 Answer

Because the carbon is sp³ hybrid.


The carbon is member from the 14th family in the periodic table. It also has 6 electrons (atomic number = 6). When we distribute those electrons, we create #1s^2 2s^2 2p^2#, but the carbon has to lower the #2p# orbitals and raise the #2s# orbitals in energy, making its #2s# and #2p# orbitals degenerate, as four #sp^3# hybridized orbitals, with one electron in each, before bonding.

Carbon needs 4 more electrons to become stable, and it gets those electrons by 4 covalent bonds.

The tetrahedral geometry is created because every single #sp^3# electron from the carbon repels the other with an equal coulombic force (wouldn't be equal if the carbon wasn't hybridized) in the s¹p³ (sp³) orbital. This creates an equal distribution to the atoms and gives it a tetrahedral geometry.