Periodic Table - Group 7 Elements

In GCSE Chemistry, Group 7 are the halogens and they are non-metals that exist as diatomic molecules, such as Cl₂ and Br₂. They react by gaining one electron to form halide ions with a 1− charge. As you go down the group, melting and boiling points increase, colour becomes darker, and reactivity decreases because the outer shell is further from the nucleus and electron gain is harder. You also learn displacement reactions, where a more reactive halogen can push a less reactive halogen out of its salt solution, helping you compare reactivity in a clear, testable way.

Key Terms

• Halogen: A Group 7 element that gains one electron in reactions and forms diatomic molecules, for example Cl₂.
• Halide ion: A 1− ion formed when a halogen atom gains one electron, such as Cl− or Br−.
• Displacement reaction: A reaction where a more reactive element replaces a less reactive one in a compound, such as chlorine displacing bromine from bromide.

Frequently Asked Questions

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