Question

The smallest ionic radius among the following.
Li
Mg
Na+
be+

Answer 1

Be+

Answer 2

Li and mg arent ions?

Answer 3

if they were, it'd be Li+ ..its hard to tell this tell w/o statistics
but if it isnt i think Be+ would be right
as said earlier

Answer 4

To answer these sorts of questions, you have to consider the number of protons and electrons each atom/ion has. This is because an atom/ion that has more protons has a stronger effective positive charge, meaning it will attract the electrons more closely to the nucleus and so give rise to a smaller radius. Also consider the general trends for atomic radius (i.e. decreases across a period but increases down a group).

Li = 3 protons, 3 electrons
Mg = 12 protons, 12 electrons
Na+ = 11 protons, 10 electrons
Be+ = 4 protons, 3 electrons

Mg and Na+ automatically have greater radii than Li and Be+ since they are in a lower period and so have an extra valence shell (between the two, Na+ has the smaller radius since it has more protons attracting fewer electrons). Li and Be are both in the same period, so we would expect Be to have the smaller radius since it is further along the period and so has more protons to create a greater positive charge to attract electrons. Since Be+ has lost one electron but still has the same number of protons, the effective charge attracting each electron is even greater, making the radius even smaller.

Therefore, the smallest radius would be Be+, followed by Li, Na+, and finally Mg.

Answer 5

ur right matt 101!!!

Answer 6

@yash2651995 - a valid concern :)

Whether Mg is or isn't an ion doesn't really matter in this case since it is in a lower period and so would have a greater radius than atoms of a higher period either way.

Just like Be normally has a smaller radius that Li, so too would Be+ have a smaller radius than Li+ for the same reason. Comparing Be+ with Li instead just makes the difference a lot more obvious.