2. Group 7 Halogens
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What is the term used to refer to halogens existing in pairs?
Halogens are diatomic, meaning they form molecules made of pairs of atoms sharing electrons.
Colour and State of Fluorine
Yellow gas
Colour and State of Chlorine
Pale yellow-green gas
Colour and State of Bromine
Red-brown liquid
Colour and State of Iodine
Grey solid
What happens to the reactivity of group 7 elements as you go down the group?
• The melting and boiling points of the halogens increase as you go down the group • This is due to increasing intermolecular forces as the atoms become larger, so more energy is required to overcome these forces • Reactivity decreases
Colour of Chlorine in a solution
Pale Green
Colour of Bromine in a solution
Orange
Colour of Iodine in a solution
Dark brown
Fluorine Characteristics
Very reactive, poisonous gas
Chlorine Characteristics
Reactive, poisonous and dense gas
Bromine Characteristics
Dense red-brown volatile liquid
Iodine Characteristics
Shimmery, crystalline solid that sublimes to form a purple vapour
Calcium Symbol equation with Bromine
Ca + Br2 → CaBr2
Non - Metal halides
• The halogens react with non-metals to form simple molecular covalent structures • For example, the halogens react with hydrogen to form hydrogen halides (e.g., hydrogen chloride)
Describe a halogen displacement reaction
A halogen displacement reaction occurs when a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide.
Why does reactivity of the halogens decrease as you go down the group?
• Halogen atoms form negative ions when they gain an electron to obtain a full outer shell • This means that the increased distance from the outer shell to the nucleus as you go down a group makes the halogens become less reactive. • More shielding means less electrostatic forces of attraction