Properties Of Alkanes

Question 1

What is an alkane?

Answer 1

• hydrocarbon chains with only single carbon to carbon bonds
• general formula: CnH2n+2

Question 2

Why are the covalent bonds in Alkanes sigma bonds?

Answer 2

• atomic orbitals on carbon and hydrogen atoms overlap
• this forms a new, shared orbital lying directly between the bonded atoms

Question 3

Describe the shape of Alkanes.

Answer 3

• each carbon is surrounded by four electron pairs in four sigma bonds
• the sigma bonds act as axes around which the atoms can rotate freely
• repulsion between these electrons pairs results in a 3D tetrahedral shape, with bond angles of 109.5 degrees

Question 4

What is the effect of chain length on the boiling point of Alkanes?

Answer 4

• the longer the chain length, the higher the boiling point
• as there is a greater number of electrons/ more points of contact so,
• the induced dipole-dipole interactions between molecules are stronger and more frequent so,
• more energy is required to break these stronger forces

Question 5

What is the effect of branching on the boiling point of Alkanes?

Answer 5

• the more branched an alkanes is, the lower its boiling point
• as, there are fewer points of contact between molecules so,
• there are fewer induced dipole-dipole forces between molecules
• which require less energy to be overcome