# What is the atomic number of an element equal to?

Jun 24, 2016

The atomic number, $Z$, is equal to the number of protons, positively charged nuclear particles, that reside in the element's nucleus.

#### Explanation:

$Z = 1$, the element is hydrogen, $Z = 2$, the element is helium, .....$Z = 6$, the element is carbon..........$Z = 17$, the element is chlorine.

Now sometimes in chemistry, when we say proton, we mean the ${H}^{+} \text{ or } {H}_{3} {O}^{+}$ ion. Here, in the context of atomic physics, we mean a massive, positively charged nuclear particle, whose number defines the identity of the nucleus.

Two questions:

$\text{Do you have to remember these numbers?}$

$\text{In the neutral ATOM how many electrons are there compared}$ $\text{to Z?}$