About Alkanes

Question 1

What are Alkanes?

Answer 1

• Saturated hydrocarbons
• Most stable organic compounds - lack of reactivity
• General formula = Cn H2n+2

Question 2

Properties of Alkanes

Answer 2

• Single covalent bonds only - each C atom is joined to 4 other atoms
• These are sigma bonds - result of overlap of 2 orbitals 1 from each bonding atom

Question 3

About Sigma Bonds

Answer 3

• Each overlapping orbital contains 1 electron so the sigma bond has 2 electrons between bonding atoms
• Positioned on a line directly between bonding atoms

Question 4

Shapes of Alkanes

Answer 4

• Each C atom surronded by 4 electron pairs w/ max. repulsion
  => results in 3D tetrahedral arrangement (109.5 bond angle)
• Each sigma bond acts as axes around which atoms can rotate freely

Question 5

Boiling Point of Alkanes

Answer 5

• Increases boiling point w/ the increase of chain length

- The more atoms = more electrons = stronger induced dipoles = more attraction between molecules

Question 6

Effect of chain length on boiling point

Answer 6

• London forces act between molecules in close contact
• As chain length increases = larger surface area
• Greater SA of contact = stronger London forces

Question 7

Effect of branching on boiling point

Answer 7

• Despite isomers of alkanes having same RAM, increase of branches lowers boiling point
• More exposed chain/ less SA of contact = weaker London Forces