Electron Configurations - Periodicity Questions And Answers (Page 3 of 3) in pdf

Electron Configurations - Periodicity Questions And Answers Page 3

13. Given this series of ionic radii:





3

2

260 pm;

171 pm;

126 pm;

119 pm;

116 pm;

86 pm;

68 pm,

estimate the atomic radius of neon. Do you think this is a fair estimate?

All these species are isoelectronic; all have the configuration [He] 2s

. However, the nuclear

charge increases along the series and the result is a decrease in the radius as the electrons are pulled

closer to the nucleus.

Somewhere between 116 and 119 pm? This is where Ne fits in the isoelectronic series. Ne does not

form compounds like the nonmetals in the preceding groups and measuring its atomic radius is

therefore difficult. Some data could be obtained from the crystalline structure of solid neon but the

bonding in such a solid is quite different from the bonding in elements like carbon or sulfur, or in

compounds like sodium fluoride. There is wide variation in stated values for the atomic radius of

neon—anywhere from 70 pm to 112 pm. Putting together a set of self-consistent data is not easy.

For example, Na+ itself is listed as having an atomic radius anywhere from 95 and 116 pm. You

. F is listed usually at about 72 pm – you might have expected

would expect Ne to be larger than Na

Ne to be smaller. However, in neon the interelectronic repulsion is high; the electrons are very

crowded. As a result, neon might well be larger than fluoride or oxygen. A value between 100 and

110 pm seems reasonable.

Electron Configurations - Periodicity Questions And Answers Page 3