Halogenoalkanes

What are they?

Saturated carbon compounds containing one or more halogen atoms.

What have they been proven to cause?

Pollution, which has led to the depletion of the ozone layer.

General formula

CnH2n+1X

C-X bond

The bond is polar therefore there are dipole dipole interactions.

Which atom is more electronegative than the C atom?

The halogen atom.

What happens to the electronegativity of the halogen atom down group 7?

Electronegativity decreases down the group. So the C-X becomes less polar.

Which element is extremely electronegative/polar?

Fluorine

What are the two intermolecular forces between Halogenoalkane molecules?

Van der waals INCREASES. Dipole-dipole interactions DECREASES.

Iodine intermolecular forces?

Strong VDW/ induced dipole-dipole forces. Weak permanent dipole- dipole forces.

The intermolecular forces?

The intermolecular forces due to VDW forces increases as the relative molecular mass increases. Therefore, the boiling point increases as the chain length increases.

The boiling point increases,

as the relative molecular mass of the halogen increases.

The bp of iodoalkane is greater than…

Bromo and chloro alkanes as iodo is a bigger molecule.

What is electronegativity?

It is a measure of an atom’s ability to attract electrons, and hold them. FONCL - these elements form polar bonds.

In water they are the same as alkanes…

Insoluble

Methane + chlorine »

Chloroalkane + hydrogen chloride gas

What colour?

Colourless

3 steps of free radical substitution

1. Initiation

2. Propagation

3. Termination

Initiation w example

Molecule »> 1 radical + 1 radical

Cl2 » 2Cl;

Ultraviolet light makes free radicals, how?

When a molecule of a halogen is exposed to UV light, breaks into 2 halogen atom free radicals. The UV light provides the energy to break covalent bond, between the 2 halogen atoms.

What are free radicals?

Atoms with unpaired electrons that are hugely reactive.

Propagation

Molecule + radical » radical + molecule

Termination w example

Radical + radical »> molecule

Cl; + Cl ; » Cl2

;CH3 + Cl; » CH3Cl

2 types of reactions of Halogenoalkanes

Nucleophilic substitution and elimination

The carbon is delta + in the C-X bond, so it is prone to…

Nucleophilic attack

What is a nucleophile?

An electron pair donor. Cleo likes to donate.

C-F

Strongest bond. Fluoroalkanes are extremely unreactive. F- is the most stable ion.

Elimination

When dissolved in ethanol, the hydroxide ions acts as a base.

;OH base

Accepts a proton (hydrogen ion) and then forms water.