Determining Lewis Structure

[Daniel Liu]

Why does a C atom normally form 4 bonds instead of 2 bonds and 2 lone pairs, for example? Is there a way we can determine this?

[Alyssa Truong 1L]

It depends on what the C is bonded to in determining how many shared bonds C has with other atoms. There isn’t really a way we can determine this, because as a rule, C will always have 4 bonds and never have lone pairs. In general, the element with lower ionization energy is the central atom and everything would be bonded to it. Thus, if C is the element with lower ionization energy, it would end up in the center instead of the outside and can then achieve the octet rule without needing any lone pairs. Since C also has 4 valence electrons, it’s very easy to have 4 different bonds to achieve stability. In the case with C and H, even though H has the lower ionization energy, it just follows the rule where H is never in the center. It is always on the outside bonded with a single bond.