Question

Which of the following statements is true concerning ethene?

• A. Both carbon atoms are $s{p}^2$ hybridized and the molecule is planar
• B. Both carbon atoms are $s{p}^2$ hybridized and all bond angles are approximately ${109.5}^o$
• C. One carbon atom is $sp$ hybridized while the other is $s{p}^2$
• D. Both carbon atoms are $s{p}^3$ hybridized and all bond angles are approximately ${109.5}^o$
• E. Both carbon atoms are $sp$ hybridized and the molecule is planar

Answer 1

Answer: (A)

Both carbon atoms are $s{p}^2$ hybridized and the molecule is planar

In the case of ethene, there is a difference from, say, methane or ethane, because each carbon is only joining to three other atoms rather than four. When the carbon atoms hybridise their outer orbitals before forming bonds, this time they only hybridise three of the orbitals rather than all four. They use the 2s electron and two of the 2p electrons, but leave the other 2p electron unchanged.
The new orbitals formed are called $s{p}^2$ hybrids, because they are made by an s orbital and two p orbitals reorganising themselves.$s{p}^2$ orbitals look rather like $s{p}^3$ orbitals that you have already come across in the bonding in methane, except that they are shorter and fatter. The three $s{p}^2$ hybrid orbitals arrange themselves as far apart as possible - which is at 120° to each other in a plane. The remaining p orbital is at right angles to them.