Modelling σ and π bonds
 Using long balloons, make a Carbon atom showing 4 sp3
orbitals in a tetrahedral arrangement around the nucleus.
Label the orbitals
 Make a methane molecule by overlapping these 4 sp3
orbitals with the s orbitals of 4 Hydrogen atoms (these are
spherical, so use round balloons). Each overlapping sp3
and s orbital forms a σ bond.
 Make an ethane molecule by overlapping 2 sp3 orbitals to
form a σ bond between 2 Carbon atoms.
 Make 2 Carbon atoms with 3 sp2 orbitals in a trigonal
planar arrangement around the nucleus and 1 p orbital
above and below (use a different coloured balloon for this p
orbital).
 Make an ethene molecule by overlapping a sp2 orbital from
each C atom to form a σ bond. Then make the p orbitals
overlap to form a π bond. What shape is the molecule?
The nature of the double bond in alkenes
1.
In alkenes, the functional group is __________
2.
In a double bond, each C atom forms 3 ____bonds by the overlap of 3
____ orbitals and 1 ___ bond by the overlap of a ____ orbital.
3.
The π bond “locks” the C atoms at either end of the bond in place and
restricts _________.
4.
This makes the shape of an ethene molecule ___________.
5.
This leads to a form of stereoisomerism, called ______________
isomerism.
6.
A C=C is stronger than a C-C bond in terms of bond enthalpies, but the
π bond is weaker that the σ bond so it will be more easily
____________ during reactions.
7.
The C=C double bond makes alkenes susceptible to attack by chemical
species which are attracted to an area of high electron density. These
species are called _______________ , which means electron loving.