Atomic & Mass Number Flashcards

All 6 cards in this deck

What is the atomic (proton) number of an atom?

The number of protons in its nucleus.

What is the mass (nucleon) number of an atom?

The total number of protons and neutrons in its nucleus.

In the nuclear symbol $^{A}_{Z}\mathrm{X}$, what do $A$ and $Z$ stand for?
e.g. $^{23}_{11}\mathrm{Na}$

$A$ is the mass (nucleon) number and $Z$ is the atomic (proton) number — so sodium has 23 nucleons and 11 protons.

How do you find the number of neutrons in a nucleus from its symbol?
e.g. $^{7}_{3}\mathrm{Li}$

1. Read the mass number (top): 7
2. Read the atomic number (bottom): 3
3. Neutrons = mass number $-$ atomic number = 4

In a neutral atom, what else does the atomic number tell you besides the number of protons?

The number of electrons.

True or false? The mass number tells you the number of neutrons in a nucleus.

False. It is the number of protons plus neutrons.