2.2.2 The Proton Number and Mass Number (Demo)

Lesson Progress

0% Complete

Define proton number/atomic number as the number of protons in the nucleus of an atom
Define mass number/nucleon number as the total number of protons and neutrons in the nucleus of an atom

Recall Protons and neutrons are located in the nucleus of an atom.
Take a look at the following diagrams representing different atoms. Count how many protons and neutrons are in the nucleus of each atom.

Complete the following table using the information from the diagram above.

Click the tabs to learn more about proton numbers and mass numbers.

Proton Number

Proton number (Z) is the number of protons in the nucleus of an atom. The proton number is also known as the atomic number.

Mass Number

Mass number (A) is the total number of protons and neutrons in the nucleus of an atom. The mass number is also known as the nucleon number.

You can represent the proton number (Z), mass number (A), and the element symbol as shown in the diagram.

For example, in the periodic table, the proton number for carbon is 6, and its mass number is 12.

Move the slider to view the example.

The number of protons and electrons

PredictThe beryllium atom has 4 positively charged protons (+4) and 4 negatively charged electrons (-4).

Click here to confirm your prediction

Beryllium atom has no overall charge.

Every atom has an equal number of protons and electrons. So atoms have no overall charge.