The compound ${\mathrm{CH}}_2=\mathrm{C}=={\mathrm{CH}}_2$

All three of the carbon atoms in the given structure of ${\mathrm{C}}_3{\mathrm{H}}_4$ are connected to one another by double bonds. Carbon is designated as ${\mathrm{C}}_1, {\mathrm{C}}_2$, or ${\mathrm{C}}_3$. Due to their 3 and 1 bonded structure, ${\mathrm{C}}_1$ and ${\mathrm{C}}_3$ are $\mathrm{sp}2$ hybridised. C2 has two bonds, two of which are sp hybridised.