Sigma and pi bonds + alkene reactivity

Compare the bond enthalpy of sigma and pi bonds

Why do sigma bonds have a higher bond enthalpy?

Due to the strong electrostatic attraction between the nuclei and shared pair of electrons due to the high electron density between nuclei

Why do pi bonds have a lower enthalpy?

Electron density is spread out above and below the nuclei HENCE electrostatic attraction is weaker

Which orbitals overlap in a sigma bond?

2 s-orbitals overlap (they align horizontally and give a single covalent bond)

Which orbitals overlap in a pi bond?

2 p-orbitals overlap in parallel

What type of bond is between C-C and C-H?

Pi bond

Draw the sigma and pi bonds in C=C

red = sigma

blue = pi

Why are alkenes more reactive than alkanes?

Alkenes are more reactive than alkanes due to their double bond being a high electron density area.

 

How are alkenes open to attack by electrophiles?

Pi bonds stick out a little and the whole double bond has a high electron density -> open to attack by electrophiles