chapyer 8- reactivity trends

What is the trend in reactivity as you go down group 7

Halogens get less reactive down the group

Halogens react by GAINING an electron in their outermost shell to form 1- ions

The atomic radius increases so valance electrons are further from the nucleus

Valance electrons are more shielded from positive nucleus going down the group (more inner electrons)

Therefore it is harder for the larger halogen (further down the group) atom to attract the one valance electron needed to form an ion

What is the trend in boiling point down group 7?

Boiling point decreases down the group

This is because with more electrons, the molecular forces become stronger therefore more energy is required to overcome these forces

(This is why fluorine is a gas and iodine is a solid- iodine has more electrons therefore more energy needed to break the intermolecular forces)

What are the three reactions halogens need to react with to undergo disproportionation?

Reaction with Water

Cl2(aq)+H2O(l)⇌HCl(aq)+HOCl(aq)

(Chlorine goes from oxidation state 0 to -1 and +1).

Reaction with Cold dilute alkali

Cl2(g)+2NaOH(aq)→NaCl(aq)+NaOCl(aq)+H2O(l)

(Chlorine goes from 0 to -1 and +1).

Reaction with hot, concentrated alkali

3Cl2(g)+6NaOH(aq)→5NaCl(aq)+NaClO3(aq)+3H2O(l)

(Chlorine goes from 0 to -1 and +5). 

Define disproportionation

A type of redox reaction where electrons from the same element are oxidised and reduced.

In the reaction of chlorine (Cl2) and sodium hydroxide (NaOH)what is the product? And what are its uses?

Product: sodium chlorate(l) aka bleach

Uses: water treatment, cleaning. Toilets, bleaching paper

What is the purpose of chlorine in water treatment? And how does it do its purpose?

Chlorine is used to kill bacteria.

How: when chlorine is mixed with water its product is hydrochloric acid (HCl) and chlorate(l) acid (HClO)

Aqueous (added to water) chlorate acid (HClO) ionises (dissociates) to make chlorate(l) ions which kill bacteria

So adding chlorine or a compound containing chlorate(l) ions to water ca make it safe to drink or swim in.

Benefits of chlorine to treat water?

It kills disease-causing microorganisms (bacteria)

Some chlorine remains in the water and prevents reinfection further down the supply

It prevents the growth of algae- eliminates bad tastes and smells, removes discolouration caused by organic compounds

Risks using chlorine to treat water?

Chlorine gas is harmful- irritates respiratory system (respiratory problems)

Liquid chlorine causes chemical burns on skin/eyes