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

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