The sodium atom contains 11 electrons, 11 protons, and 12 neutrons. What is the mass number of sodium?

2 Answers
May 11, 2017

Explanation:

The mass number is the sum of the neutrons and protons in an atom.
So 11 protons + 12 neutrons= 23

May 11, 2017

We have the ""^23Na isotope.........i.e. "mass number"=23.

Explanation:

A sneakier question would have asked:

"an atom contains 11 protons, and 12 neutrons; how may electrons" "in the neutral atom; what is the atom?".

The sum of neutrons and protons, the massive nuclear particles, gives the mass number, with which we often label the elemental symbol as a left hand superscript. But the number of "nucular protons", i.e. Z, UNEQUIVOCALLY identifies the atom; Z=11 for sodium, Z=10 for neon; Z=12 for magnesium.

It is not too difficult to incorporate these ideas into your understanding, and if you have a Periodic Table in front of you (and you should have one NOW!) these problems are straightforward.