3.1.3 The Halogens

Which group are the halogens?

7

As you go down group 7 how does state change?

goes from gas (flourine and chlorine) to liquid (bromine) to solid (iodine and astatine)

As you go down group 7 how does colour intensity change?

it gets darker/ increases

What type of molecules are group 7?

diatomic

What is the bonding and structure of group 7 molecules?

• simple covalent molecules

• covalent intra

• london forces inter

Describe the melting point of halogens?

low

Why do halogens have a low boiling point?

little heat energy is required to break the week induced dipole-dipole forces between the molecules

What forces exist between diatomic halogen molecules?

induced dipole dipole forces

What happens to meting and boiling point as you go down group 7?

increase down the group

Why does melting and boiling point increase as you go down group 7?

• more shells

• more electrons

• more induced dipole-dipole forces between the molecules

• more heat energy is required to break them

What type of agents are group 7 elements?

oxidising agents

What are oxidising agents?

elements that remove elements from other species to get reduced

When group 7 elements react are they oxidised or reduced?

reduced (gain electrons)

Define oxidising power

a measure of the ability of a halogen atom to be able to attract and capture an electron from another species to form a halide ion

As you go down the halogens how does reactivity change?

it decreases

Which is the most reactove halogen?

Flourine

Why does reactivity decrease as you go down the halogens?

• more shells

• greater shielding

• atomic radius increases

• weaker nuclear attraction on the outer most electrons

• nucleus is less able to attract and capture an electron into its outer shell

• oxidising power decreases

What type of reaction are displacement reactions?

redox

What do displacement reactions of halogens show?

that reactivity decreases down the group

What is a displacement reaction?

a reaction in which a more reacrive element displaces a less reactive element from an aqueous solution of its halide ions

What is the colour of chlorine dissolved in water?

pale green

What is the colour of chlorine dissolved in organic solvent?

pale green

What is the colour of bromine dissolved in water or organic solvent?

orange

What is the colour of iodine dissolved in water?

brown

What is the colour of iodine dissolved in organic solvent?

purple

What is a disproportionation reaction?

a reaction in which the same element is both oxidised and reduced

Give an example of the disproportionation of chlorine?

chlorine + water

What is the equation for the reaction of water and chlorine?

Cl2 + H2O → HClO + HCl

What is HClO?

chloric (II) acid

Why is the production of chlorine water a disproportionation reaction?

chlorine is both reduced (Cl → Cl- in HCl) and oxidised (Cl → Cl+ in HClO)

What is chlorine water used for?

to kill bacteria in water (drinking water, swimming pools)

What is the active incredient in chlorine water?

ClO-

What is the advantage of chlorine being added to drinking water?

it kills bacteria

What is the disadvantage of chlorine being added to drinking water?

chlorine is toxic

Why is chlorine toxic?

it forms carcinogenic chlorinated hydrocarbons

What is the equation for the reaction of chlorine and cold and dilute aqueous sodium hydroxide?

Cl2 + 2NaOH → NaClO + NaCl + H2O

What is NaClO?

sodium chlorate

Why is the reaction of chlorine and aqueous sodium hydroxide important?

sodium chlorate is used in household bleach

What is the active ingredient in bleach?

ClO-

When is NaClO formed vs when NaClO3?

NaClO is formed when the aqueous NaOH is cold and dilute, but NaClO3 is formed when the NaOH is hot and concentrated

What is the chemical test for halide ions?

aqueous silver nitrate solution is added dropwise

What is the general equation for the silver nitrate - halide test?

X- + Ag+ → XAg

What colour is AgCl?

white

What colour is AgBr?

cream

What colour is AgI?

yellow

If the precipitate test can not easily show what halide is present, what further test can be done?

adding aqueous ammonia solution

When dilute aqueous amonia is added to

• silver chloride

• silver bromide

• silver iodide

What happens?

• dissolves

• does not dissolve

• does not dissolve

When concentrated aqueous amonia is added to

• silver chloride

• silver bromide

• silver iodide

What happens?

• dissolves

• dissolves

• does not dissolve