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

2 Answers
May 11, 2017

Answer:

Explanation:

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

May 11, 2017

Answer:

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.