Trends in the sizes of ions (ionic radii)

Q1. What is the trend as we go down a group?

Q2. How can we explain the trend?

Q3. How would the atomic radius compare with the ionic radius for a CATION and its’ parent atom?

E.g. Na+ ionic radius and the Na atomic radius

Q4. How would the atomic radius compare with the ionic radius for an ANION and its’ parent atom?

E.g. Br- ionic radius and the Br atomic radius

Data on next slide.

Q5. What trend would you expect in ionic radii across a period?

Eg. Period 3 Na Ar

Use the extract from the Edexcel Data Booklet to find the ionic radii of the elements in Period 3:

Ion: Na+ Mg2+ Al3+ Si4+ P3- S2- Cl-1

Radius:(nm)

Excel chart on next slide

How can we explain this trend?

Comparing ionic radii of isoelectronic ions

E.g. Al3+ and N3-

Both have the electron configuration: 1S2 2S2 2P6

Which would be the largest ion? Why?

Use the data booklet extract to find the ionic radii of three more isoelectronic ions.

Explain the trend in the ionic radii of the ions you choose.

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Typical exam question on trends in ionic radii:

IONIC BONDING PPQs