Atomic number and mass number | Exit Quiz | Oak National Academy

What does the atomic number of an element indicate?

• the number of neutrons

• the number of protons

• the total number of protons and neutrons

• the number of electrons in a neutral atom

Answer explanation

The atomic number (proton number) is crucial as it defines the element by stating the number of protons in its nucleus, it also tells us how many electrons there are in a neutral atom of this element as the proton and electron numbers are equal.

True or false? The atomic number is equal to the number of electrons in a neutral atom.

• True

• False

Answer explanation

In a neutral atom, the number of electrons equals the number of protons, which is the atomic number.

What is the relative atomic mass?

• the mass of protons

• the mass of neutrons

• the total mass of an atom

• the average mass of an atom compared to carbon-12

• the total number of protons and neutrons in the nucleus of an atom

Answer explanation

It's a mean value (it's why some elements don't have whole numbers for their relative atomic mass).

If an atom has an atomic number of 6, how many electrons does it have?

Answer explanation

It has 6 electrons. The atomic number equals the number of protons, and in a neutral atom, the number of electrons equals the number of protons.

How does the mass number differ from the atomic number?

• mass number includes electrons

• mass number is only about protons

• mass number includes protons and neutrons

• there is no difference

Answer explanation

Unlike the atomic number, it sums both protons and neutrons in the nucleus.

An element has a mass number of 23 and an atomic number of 11. How many neutrons does it have?

Answer explanation

Mass number (23) minus atomic number (11) gives the number of neutrons (12).