An alkane with one or more hydrogen atoms replaced by halogen atoms.

Halogenoalkanes can also be called haloalkanes.

Because halogens are more electronegative than carbon, so they pull the shared electrons towards them, giving the carbon a partial positive charge.

Bond enthalpy is the energy required to break one mole of covalent bonds between two atoms in the gaseous state.

As we descend group 7, the carbon-halogen bond enthalpy decreases.

This is because the atomic radius of the halogens increases which leads to a longer carbon-halogen bond and a weaker attraction of the shared pair of electrons in the bond to the halogen nucleus.

A nucleophile is an electron-pair donator.

A nucleophile is an electron-rich species that donates a pair of electrons in a reaction. Examples of nucleophiles include OH^-, CN^- and Br^-.

The halogen atom is replaced by a nucleophile.

Halogenoalkanes are warmed with aqueous alkali to produce an alcohol. A hydrolysis reaction occurs.

RX + OH^- ➔ ROH + X^-

The OH^- ion acts as the nucleophile, donating a pair of electrons to the carbon atom bonded to the halogen.

This breaks the carbon-halogen bond and forms a new carbon-oxygen bond.

Heterolytic fission

The bond breaks to give a halide ion and a carbocation.

The rate of hydrolysis increases in the order: chloroalkanes < bromoalkanes < iodoalkanes. 

This is due to the decrease in bond enthalpy of the carbon halogen bond in the order C-Cl > C-Br > C-I.

The fastest rate of hydrolysis occurs in iodoalkanes because the C-I bond is the weakest. 

1. Free radical substitution of alkanes by chlorine or bromine in UV light.
2. Electrophilic addition of alkenes with a halogen or hydrogen halide at room temperature.
3. Substitution of alcohols e.g. by reactions of halide ions in the presence of acid.

1. Set up 3 test tubes with ethanol and drops of 1-chlorobutane, 1-bromobutane, and 1-iodobutane.
2. Heat the test tubes in a water bath at 50°C along with a tube of silver nitrate solution.
3. Add the silver nitrate to each test tube and start timing.
4. Observe the time taken for the silver halide precipitate to form in each tube.
5. 1-Iodobutane forms the precipitate fastest, 1-bromobutane forms the second fastest, and 1-chlorobutane forms the slowest.

1. Carry out a hydrolysis reaction in ethanol with aqueous silver nitrate:

RX_(aq) + H₂O_(l)  ➔ ROH_(aq) + H⁺_(aq) + X^-_(aq)

1. The halide ions produced react with silver ions to form a silver halide precipitate:

Ag⁺_(aq) + X^-_(aq) ➔ AgX_(s)

1. The colour of the precipitate indicates which halogen is present - AgCl is white, AgBr is cream and AgI is yellow.