Dictionary of Chemistry [6th Ed.]

clei (in a bond involving two atoms)
and there are corresponding molecu-
lar orbitals for electrons (see illustra-
tion). It is convenient in considering
these to regard them as formed by
overlap of atomic orbitals. In a hydro-
gen molecule the s-orbitals on the
two atoms overlap and form a mo-

lecular orbital between the two nu-

clei. This is an example of a sigma or-

bital. In a double bond, as in ethene,

one bond is produced by overlap

along the line of axes to form a

sigma orbital. The other is produced

by sideways overlap of the lobes of

the p-orbitals (see illustration). The

387 orbital

o

x

y

z

symmetrical

s-orbital

x

y

zz

x

y

px py pz

y

x

z

three equivalent p-orbitals, each having 2 lobes

Atomic orbitals

p-orbitals

H

H H

H

C C

pi orbital

H

H

CC

H

H

hybridsp 3 -orbitals sigma orbital

Molecular orbitals: formation of the double bond in ethene

Orbital