# If an atom of tin has a mass number of 118 and an atomic number of 50, how many electrons does it have?

Jul 21, 2017

$\text{FIFTY, 50}$

#### Explanation:

Atoms are composed of electrons, fundamental particles of negligible mass with unit negative charge, that are conceived to whizz around a nuclear core containing neutrons, massive particles of zero electric charge, and, protons, massive particles of positive electric charge. In the NEUTRAL ATOM, necessarily, there are AS MANY PROTONS AS THERE ARE ELECTRONS. The nucleus also contains a number of neutrons, massive particles of zero electric charge, and these engage with nuclear protons in the strong nuclear force, an attractive force, which, at impossibly short nuclear ranges, is strong enuff to overcome electrostatic repulsion between the like charges expressed by the protons. In this atom, there are necessarily 68 neutrons if the atomic mass is 118. Why $\text{necessarily}$?

The number of protons defines $Z$, which gives the identity of the element. The (varying) number of neutrons gives rise to the phenomenon of isotopes.

And by the way. what is the element? You should be able to tell us after you consult the Periodic Table.