Chemistry

2. Inorganic Chemistry
2.1 Group 1 (Alkali Metals) – Lithium, Sodium and Potassium>2.2 Group 7 (Halogens) – Chlorine, Bromine and Iodine>2.3 Gases in the Atmosphere>2.4 Reactivity Series>2.5 Extraction and Uses of Metals>2.6 Acids, Alkalis and Titrations>2.7 Acids, Bases and Salt Preparations>2.8 Chemical Tests>

1. Principles of Chemistry

1.2 Elements, Compounds & Mixtures >1.3 Atomic Structure >1.4 The Periodic Table >1.5 Chemical Formulae, Equations and Calculations >1.6 Ionic Bonding >1.7 Covalent Bonding >1.8 Metallic Bonding >1.9 Electrolysis >

3. Physical Chemistry

3.1 Energetics >3.2 Rates of Reaction >3.3 Reversible Reactions and Equilibria >

4. Organic Chemistry

4.1 Introduction >4.2 Crude Oil >4.3 Alkanes >4.4 Alkenes >4.5 Alcohols >4.6 Carboxylic Acids >4.7 Esters >4.8 Synthetic Polymers >

2.2 Group 7 (Halogens) – Chlorine, Bromine and Iodine

2.2.1 Know the colours, physical states (at room temperature) and trends in physical properties of these elements

GROUP 7 ELEMENTS

They are known as halogens
Poisonous non-metals
Similar chemical properties because they have the same number of electrons in the outer shell
Halogens are diatomic, meaning they form molecules with two halogen atoms sharing electrons

Trends in physical properties

TREND 1:

Melting and boiling points increase down the group

Size of halogen molecules increases down the group
Increasing intermolecular forces
More energy is required to overcome the forces

TREND 2

At room temperature, the physical state of halogens changes down the group

This is also due to the increasing intermolecular forces

TREND 3

Colours of halogens changes down the group

Becomes darker

2.2.2 Use knowledge of trends in Group 7 to predict the properties of other halogens

RECALL: (DOWN THE GROUP)

Melting and boiling points increase
Colour becomes darker
Physical state at room temperature starts from gas, to liquid, to solid

Halogens can also react with metals and non–metals to form compounds

Halogen + Metal
Halogen + Non–metal
This can be used to predict the properties of other halogens as they share similar chemical properties

REACTION 1 HALOGEN + METAL

Halogen + Metal → Metal halide (salt, ionic compound)

Metals lose electrons from the valence shell
The electron(s) is
gained by the halogen, forming halide ions with 1– charge
E.g. sodium + chlorine → sodium chloride

2Na + Cl2 → 2NaCl

E.g. calcium + bromine → calcium bromide

Ca + Br2 → CaBr2

REACTION 2 HALOGEN + NON-MENTAL

Halogens + Non-metal → simple covalent compounds

Halogens are also non-metals
Non–metals tend to gain electron(s) to become more stable
When non–metals bond together, they share electrons and form covalent compounds (Topic 7: Covalent Bonding)

Halogens + Hydrogen → Hydrogen halide

E.g. chlorine + hydrogen → hydrogen chloride

Cl2 + H2 → 2HCl

2.2.3 Understand how displacement reactions involving halogens and halides provide evidence for the trend in reactivity in Group 7

HALOGEN DISPLACEMENT REACTION

A more reactive halogen can displace a
less reactive halide in an aqueous solution
- E.g. Cl₂ can displace Br^– ions in a solution to become Cl^–
Whether or not the reaction can happen tells us which halogen is more reactive

REACTIVITY OF HALOGENS

The reactivity decreases down the group
Only reactions with chlorine, bromine and iodine will be studied
Reactivity Cl > Br > I, which means:
- Chlorine can displace bromide and iodide
- Bromide can displace iodide

Chlorine with bromides & iodides

Chlorine will displace bromide or iodide ions in a solution:

Cl₂+ 2KBr → 2KCl + Br₂

Chlorine + Potassium bromide → potassium chloride + Bromine

Cl₂+ 2KI → 2KCl + I₂

Chlorine + Potassium iodide→ potassium chloride + Iodine

Bromine with iodides

Bromine will displace iodide ions in a solution:

Br₂+ 2KI → 2KBr + I₂

Bromine + Potassium iodide → potassium bromide + Iodine

2.2.4C Explain the trend in reactivity in Group 7 in terms of electronic configurations

RECALL

The reactivity of group 7 decreases down the group

WHEN HALOGENS REACT

Halogens have 7 electrons in the outer shell
When halogens react, they only need to gain one electron
As a result, it forms an anion with 1– charge

EXPLANATION OF TREND IN REACTIVITY

Reactivity of halogen depends on how easily the electron is gained