Explaining the trend in the reactivity of the halogens
3 marks · NormalExplain why astatine is less reactive than bromine, in terms of atomic structure and electronic configuration.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
Astatine has a larger atomic radius than bromine, so its outer shell is further from the nucleus. The attraction between the nucleus and an added electron is weaker in astatine, so it is harder for an astatine atom to gain an electron and form At⁻. Therefore, it is less reactive than bromine.
Must show: Astatine has larger atom/atomic radius, Outer electron shell is further from nucleus, Weaker attraction for incoming electron, More difficult to form ion
Common mistakes: Saying astatine is more reactive; Not mentioning distance from nucleus or attraction
Show mark scheme and worked solution
Marking points
M1 · 1 mark · States that astatine atom is larger / outer shell further from nucleus
M2 · 1 mark · States weaker attraction from nucleus for incoming electron
A1 · 1 mark · Relates to reactivity: harder to form At⁻, so less reactive than bromine
Worked solution
Astatine atoms are larger than bromine atoms, so the added electron joins a shell further from the nucleus in astatine. Therefore, the electron is less strongly attracted to the nucleus. This makes it harder for astatine to gain an electron and form an ion, so astatine is less reactive than bromine.