AQA GCSE Chemistry
AQA GCSE Chemistry
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Topic 1: Atomic structure and the periodic table
Topic 1: Atomic structure and the periodic table
Group 7
Group 7
The Group 7 elements, known as the halogens, include fluorine, chlorine, bromine, iodine, and astatine. These elements are non-metals and form molecules that consist of pairs of atoms (diatomic molecules). Each halogen has seven electrons in its outer shell, which explains their similar chemical reactions.
Halogens can form molecular compounds by sharing electrons with other non-metals through covalent bonding.
When halogens react with metals, they form ionic compounds where the halogen gains one electron to form a negative ion (e.g., Cl⁻, Br⁻, I⁻). For example, when sodium reacts with chlorine, it forms sodium chloride (NaCl).
Properties of halogens
Properties of halogens
As you move down Group 7:
The halogens become less reactive because it is harder for them to gain an extra electron. This is due to the increased distance between the outer shell and the nucleus, reducing the attraction. For example:
Fluorine is the most reactive and exists as a pale yellow gas.
Chlorine is a green gas
Bromine is a dense, red-brown liquid
Iodine is the least reactive of these four and exists as a dark grey solid that can form a purple vapor when heated.
Relative atomic mass increases.
The elements have higher melting and boiling points.
Reactivity
Reactivity
A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt. For example, chlorine can displace bromine from a solution of potassium bromide.
Example Reaction:
Example Reaction:
In a displacement reaction:
Cl2 (aq) + 2KBr(aq) → 2KCl(aq) + Br2 (aq)
Chlorine + potassium bromide → potassium chloride + bromine
Chlorine, being more reactive, displaces bromine from potassium bromide, resulting in the formation of potassium chloride and bromine.
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