# What is the atomic number for helium?

The nucleus of the helium atom contains 2 massive, positively charged particles. Thus, $Z$, the atomic number $=$ $2$.
$Z$ 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.
Given the examples, $Z = 1$, hydrogen; $Z = 2$, helium; $Z = 3$, lithium;.................$Z = 80$, mercury, how many electrons does each neutral element contain? Why?