# Why don't B, C, Si, have ionic forms?

Also, why can some elements such as $\ce{Fe}$ have different ionic forms such as $\ce{Fe^{2+}}$ and $\ce{Fe^{3+}}$? What determines each form?

• Although this is not an explanation, do you know about the octet rule, ionisation energies, etc? We do btw see carbocations, but they aren't very stable. – Brian Feb 7 '14 at 7:28

Boron: borates, borides. $\ce{MgB2}$ is the highest temperature BCS superconductor by a large margin.
Carbon: carbonates, carbides, hexacoordinate carbon in complexes, organolithiums, Grignard reagents, carbenium ions ($\ce{Ph3C+}$). $\ce{Al4C3}$ hydrolyzes to methane.