# What is the atomic number for helium?

##### 1 Answer
Apr 2, 2016

The nucleus of the helium atom contains 2 massive, positively charged particles. Thus, $Z$, the atomic number $=$ $2$.

#### Explanation:

$Z$ is simply the number of protons, massive, positively charged particles, present within the nucleus. $Z$ thus defines the identity of the element: $Z = 1$, hydrogen; $Z = 2$, helium; $Z = 3$, lithium;.................$Z = 80$, mercury.

You do not have to remember these numbers, because in every exam you ever sit you should be provided a copy of the Periodic Table, which lists all the elements in order of atomic number. Of course, you still have to be able to use the table.

Given the examples, $Z = 1$, hydrogen; $Z = 2$, helium; $Z = 3$, lithium;.................$Z = 80$, mercury, how many electrons does each neutral element contain? Why?