Question

How would you arrange the ions `N^-3`, `O^-2`, Mg2+, Na+, and F- in order of increasing ionic radius?

Answer 1

`""_12Mg^"-3"< ""_11Na^"+"<""_9F^"-"<""_8O^"-2"<""_7N^"-3"`

Explanation:

If the ions derived from different atoms are isoelectronic species, then they all have same number of electrons in their electronic shells and will have got same electronic configuration but their nuclear charge will differ because of their difference in number of protons in the nucleus. With increase in number of protons in the nucleus the electrons are more attracted towards nucleus thereby causing the decrease in ionic radius. On this principle our problem will be solved

The given ions are

• `""_7N^"-3"->"no. of proton"=7 and" no of electron"=10`
• `""_8O^"-2"->"no. of proton"=8 and" no of electron"=10`
• `""_9F^"-"->"no. of proton"=9 and" no of electron"=10`
• `""_11Na^"+"->"no. of proton"=11 and" no of electron"=10`
• `""_12Mg^"-3"->"no. of proton"=12 and" no of electron"=10`

Hence the increasing order of ionic radius is

`""_12Mg^"-3"< ""_11Na^"+"<""_9F^"-"<""_8O^"-2"<""_7N^"-3"`

To rmember ->For isoelectronic species lower the nuclear charge higher the radius