Properties of alkanes

—> saturated : carbon-carbon single bonds only
Alkanes contain single C-C and C-H bonds only

—> general formula : CnH2n+2

—> used as fuels because they have a high bond Enthalpy and this generates a lot of energy (when bond is broken energy is released)

—> the single C-C and C-H bonds are called sigma bonds

—> sigma bond : overlap of orbitals directly between the bonding atoms

—> alkenes = sp2 hybridisation
(sp2 : only is and 2p orbitals hybridise, 1 is left)

—> electronic configuration of C in excited state
(the unhybridised orbitals overlap side ways and form the 2 second bond in alkenes)

—> pi bond : sideways overlap of adjacent p-orbitals above and below the bonding carbon atoms

—> restricted rotation

—> everything has a sigma bond

—> double bonds have 1x sigma bonds & 1x pi bond

—> triple bonds have 2x pi bonds and 1x sigma bonds

—> s2 : 1 electron moved in to P
—> then 3 orbital joins hybridisation

(Name : bond angles : length : strength)
Alkanes : 109.5 C-H : longest : weakest
Alkenes : 120 C=C : shortest : strongest
Benzene : 120 : mid : mid

Alkenes :

• more electrons between carbons
• more electrons attracted to nuclei
• overlap of the pi orbitals which pulls carbons closer together
• shortest length

—> carbon forms 4 bonding pairs

—> tetrahedral shape

—> 109.5°C

—> bonding pairs repel each other equally

—> sigma bond = single covalent bond

—> overlap of orbitals directly between the bonding atoms

—> atoms are able to rotate freely around sigma bond (molymod)

—> as the number of carbons and hydrogens increases, the chain gets longer

1. Electrons increase
2. VDW increases
3. More energy needed to overcome this

—> as atoms increase, the boiling point increases
—> more energy needed to break the imf between the molecules

VDW : induces dipole dipole interactions

Explain why propane had a higher bp than methane?

• more points of contact/surface interaction
• stronger induced dipole-dipole interaction (vdw)
• more energy needs to break the IMF (vdw)

—-

• methylpropane has a less surface interaction
• fewer induced dipole-dipole interaction
• methylpropane has weaker induced dipole-dipole interaction
• less energy needed to break the IMF in methylpropane chains