4. alkenes

Question 1

general formula

Answer 1

Cn H2n

Question 2

what is a double bond made up of

Answer 2

a sigma bond and a pi bond

Question 3

a sigma bond is formed when

Answer 3

2 s orbitals overlap (spherical)
2 s orbitals overlap in straight line giving highest possible electron density between 2 nuclei.
single covalent bond
high electron density between nuclei = strong electrostatic attraction between nuclei and shared pair of electrons
high bond enthalpy. strongest type of covalent bond

Question 4

e.g of sigma bonds

Answer 4

C-C

C-H

Question 5

a pi bond is formed by

Answer 5

sideways overlap of 2 adjacent p orbitals

2 parts - above an below molecular axis because p orbitals are dumbbell shaped

Question 6

why are pi bonds weaker than sigma bonds

Answer 6

electron density is spread out above and below nuclei
electrostatic attraction between nuclei and shared pair of electrons is weaker
relatively low bond enthalpy

Question 7

why are alkanes unreactive

Answer 7

alkanes only contain C-C and C-H sigma bonds. high bond enthalpy, difficult to break. bonds non-polar so dont attract nucleophiles of electrophiles

Question 8

why are alkenes reactive

Answer 8

C=C double bond 4 electrons, high electron density. pi bond sticks out above and below rest of molecule.
pi bond is likely to be attacked by electrophiles.
low bond enthalpy of pi bond

Question 9

why are alkenes good starting points for making other organic compounds

Answer 9

very reactive.

Question 10

why are double bonds stronger than single bonds

Answer 10

combined strength of pi and sigma bond