Chemistry CCEA AS Level 2.4 (Alkenes)

What is the general formula of an alkene?

CnH2n

Why are alkenes classed as unsaturated hydrocarbons?

The contain at least one carbon-carbon double/triple covalent bond and only carbon and hydrogen atoms

What is a sigma bond?

A covalent bond formed by the linear overlap of atomic orbitals resulting in the free rotation along the bond axis

What is a pi bond?

A covalent bond formed by the sideways overlap of p orbitals resulting in it being restricted along the bond axis

Why are alkenes more reactive than alkanes?

The weaker pi bond is more easily broken

What is an electrophile?

An ion or molecule that attacks regions of high electron density

What is heterolytic fission?

Bond breaking where both shared electrons go to one atom

What is a primary carbocation?

A carbocation with one carbon directly attached to the positively charged carbon

What is a secondary carbocation?

A carbocation with two carbons directly attached to the positively charged carbon

What is a tertiary carbocation?

A carbocation with three carbons directly attached to the positively charged carbon

What are the conditions needed for alkenes to react with hydrogen?

- Nickle catalyst

- 150°C

What do alkenes form with hydrogen?

The corresponding alkane

What do alkenes form with halogens?

The corresponding dihalogenoalkane

What colour change will be seen with an alkene in bromine water?

Orange to colourless

What do alkenes form with hydrogen halides as room temperature?

The corresponding halogenoalkane

What to alkenes form with steam in the presences of a phosphoric acid catalyst and under high temperature and pressure?

The corresponding alcohol

What are alkenes with two double bonds known as?

Dienes

What is polymerisation?

Joining together of small molecules (monomers) to form a larger molecule

What is a monomer?

A small molecule that joins to form a polymer

What is a polymer?

A larger molecule formed when monomers join together

What is a repeat unit?

A specific arrangement of atoms that occurs in a structure over and over