Ionic Trends (Edexcel AS Chemistry)

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Ionic Radius

Ionic radius

  • The ionic radius of an element is a measure of the size of an ion
  • Ionic radii show predictable patterns
    • Ionic radii increase with increasing negative charge
    • Ionic radii decrease with increasing positive charge
  • For negative ions
    • They are formed by atoms gaining electrons 
    • The outermost electrons are further away from the positively charged nucleus and are therefore held only weakly to the nucleus which increases the ionic radius
    • The greater the negative charge, the larger the ionic radius
  • For positive ions
    • Positively charged ions are formed by atoms losing electrons
    • The nuclear charge remains the same but there are now fewer electrons which undergo a greater electrostatic force of attraction to the nucleus which decreases the ionic radius
    • The greater the positive charger, the smaller the ionic radius

Atomic Structure Ionic Radius Trends, downloadable AS & A Level Chemistry revision notes

Trends in the ionic radii across a period and down a group

Isoelectronic Ions

  • These are ions that have the same electronic configuration 
  • For example the following ions all have the electronic configuration of 1s2 2s2 2p6
  • However, they all have different numbers of protons, therefore will have a different ionic radius
    • N3- (7 protons)
    • O2- (8 protons)
    • F- (9 protons)
    • Na+ (11 protons)
    • Mg2+ (12 protons)
    • Al3+ (13 protons)
  • As the number of protons in the nucleus of the ion increases, the electrons get pulled in more closely to the nucleus
  • The radii of the isoelectronic ions therefore fall across this series of ions 
    • N3- has an ionic radius of 0.171 nm and Al3+ has an ionic radius of 0.054 nm

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Philippa

Author: Philippa

Expertise: Chemistry

Philippa has worked as a GCSE and A level chemistry teacher and tutor for over thirteen years. She studied chemistry and sport science at Loughborough University graduating in 2007 having also completed her PGCE in science. Throughout her time as a teacher she was incharge of a boarding house for five years and coached many teams in a variety of sports. When not producing resources with the chemistry team, Philippa enjoys being active outside with her young family and is a very keen gardener.