The atomic number of nitrogen is 7. How many protons, neutrons, and electrons make up an atom of nitrogen-15?

1 Answer
Nov 26, 2015


By definition, if #Z#, the atomic number #=# #7#, then there are 7 protons, 7 electrons, and 8 neutrons!


The atomic number is by definition the number of protons, positively charged particles, contained within the atomic nucleus. So if there are 7 protons, there MUST be 7 electrons, 7 negatively charged particles. Why? Because matter is electrically neutral, and positive and negative particles must be equal.

Electrons have negligible mass; the mass number depends on the number of protons contained within the nucleus, PLUS the number of neutrons. Given that we have #""^15N#, there must be 8 neutrons contained within the nucleus. Capisce?