electron of a carbon not involved in sigma bonding is used in pi bonding where there is a sideways overlap of two p orbitals. each carbon atom contributes one electron to the pi bond.
pi bond rotation
no rotation available as the pi bond locks the two carbon atom into place
shape around a double bond
three regions of electron density around each of the carbon atoms which repel as far apart as possible making it 120
stereoisomers
same structural formula but different arrangement of atoms in space
