Alkanes

Alkanes

• General Formula - C_nH_2n+2

• Only contains C and H atoms

• Each C atom has 4 bonds

• Saturated - only contain single bonds

• Cycloalkanes - when the C atoms form a ring structure (C_nH_2n)

Shapes of alkanes

• 4 bonding pairs of electrons

• Arranged in a tetrahedral shape due to the equal repulsion of electron pairs

• Bond angle = 109.5°

• e.g, Methane (CH₄)

  

How structure affects boiling points

• Boiling point of an alkane is influences by the strength of its intermolecular induced dipole-dipole forces, which vary based on length of the carbon chain and the extent of branch

• Carbon chain length

  • Longer C chain means more electrons creating stronger temporary induced dipole

  • These stronger dipoles result in stronger induced dipole-dipole forces between molecules

  • More energy is needed to overcome these forces and boil the alkane

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• Branching

  • Straight chain alkanes can pack together more closely, maximising interaction between molecules.

  • This leads to stronger induced dipole-dipole forces in straight chain alkanes

  • Therefore, more energy is required to seperate these molecules

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