# What is the difference between nuclear charge and ionic charge?

There was a question asking why magnesium metal has a higher melting point than sodium.

• Magnesium has more delocalised electrons.
• Magnesium ions have a greater positive charge.
• Magnesium has a greater electrostatic attraction between ions and delocalised electrons.

However, in the mark scheme in the additional guidance, it also said the mark couldn't be given if you said:

Magnesium ions have a great nuclear charge rather than greater positive charge.

I was confused as to what the difference is.

• What is your weight? Now what is the weight of your skeleton? Is there any difference? – Ivan Neretin May 5 '18 at 7:34
• Comments are not for extended discussion; this conversation has been moved to chat. – Loong May 6 '18 at 6:45

Nuclear charge is the charge present inside a nucleus, due to the protons. For example, a carbon atom has $+6e$ nuclear charge.
Ionic charge is the charge due to the gain or loss of electrons in the valence shell. So, the sodium ion has an ionic charge of $+1e$ (due to loss of one valence electron). That ion's nuclear charge is still $+11e$ (there are still 11 protons only).