# What is an atomic number?

Mar 22, 2016

#### Answer:

The atomic number, $Z$, is the number of protons, massive positively charged particles, contained in the element's nucleus.

#### Explanation:

$Z$ defines the identity of the element. If $Z$ $=$ $1$, the element is hydrogen; if $Z$ $=$ $2$, the element is helium; if $Z$ $=$ $19$, the element is potassium; if $Z$ $=$ $92$, the element is uranium.

How do I know this? Well, in every examination of chemistry and physics you will ever sit, you will be given a Periodic Table, which lists the atomic number and atomic mass of EVERY element. Of course, you will have to be able to use the table, so get cracking.