Why can't carbon form 4 bonds?



The Cohesion (also bond value) denotes the number of atomic bonds that are entered into by an atom. In the Lewis or structural formula, it is expressed by the number of valence lines, starting from an atom.

For example, the two carbon atoms (C) in ethane (C2H6) four-bond, i.e. they have a bond of 4 because they have four bonds. The hydrogen atoms (H) are one bond with their one bond. In ammonia (NH3) the nitrogen atom (N) has three bonds and the hydrogen atoms again have one bond.

The cohesiveness is mainly determined by the number of singly occupied atomic orbitals (AO). A singly occupied orbital is an orbital in which there is only one electron. The hydrogen has a single occupied s-orbital (1s1), which is why it is unified. There are three singly occupied p orbitals (1s2, 2s2, 2p3) responsible for ensuring that it is three-bind.

However, it must be taken into account here that there are also elements that are excited by hybridization to an energetically higher state before binding, so that the number of singly occupied hybrid orbitals counts here. An example of this is carbon, which in the ground state is due to its two singly occupied p orbitals (1s2, 2s2, 2p2) would be two-string. However, before bonding, the carbon becomes the valence state (1s2, 2sp3) encouraged, in which 4 singly occupied sp3-Orbitals exist, so that it can enter into four bonds, i.e. it is four-bonded.

Atoms with lone pairs of electrons are another exception. Here, these lone pairs of electrons can be used for a bond (coordinative bond) by introducing the two electrons of the electron pair into the bond. An example here is the nitrogen in the ammonium ion (NH4+) binds to four hydrogens because it has entered into a fourth bond with its lone pair of electrons, i.e. it is four-bonded.

Category: Chemical Bond