Subatomic particles and atomic number

What you need to know

• Protons have relative charge +1, neutrons 0 and electrons −1.
• In the nuclear model, protons and neutrons are in the nucleus and electrons surround the nucleus.
• Atoms have equal numbers of protons and electrons, so they have no overall electrical charge.
• Atomic number means number of protons; all atoms of one element share that proton number, while different elements have different proton numbers.

The big picture

Atoms contain protons, neutrons and electrons. Protons have relative charge +1, neutrons 0 and electrons −1; in the nuclear model, protons and neutrons are in the nucleus while electrons surround it. An atom has equal numbers of protons and electrons, so their opposite charges balance and the atom has no overall electrical charge. The number of protons is the atomic number, and that proton number identifies the element.

Tap any cell to reveal it. Tap a column header to read one property down every item.

From proton count to element

Follow the proton number; it is the identifying number.

1. 1

   Count the protons

   The proton count is the starting information because atomic number is defined by the number of protons.

2. 2

   Read the atomic number

   The number of protons is the atom's atomic number, so the two values are the same.

3. 3

   Identify sameness

   Atoms with the same proton number are atoms of the same element because all atoms of one element share that proton number.

4. 4

   Spot a different element

   A different proton number means a different atomic number and therefore a different element.

Predict, then check

Use both atomic number and charge balance.

An atom has 11 protons and 11 electrons. Which description must be correct?

Memory hook

PEN for charge: Proton Positive, Electron Negative, Neutron Neutral.

Check yourself

Why do two atoms with different numbers of protons have to be atoms of different elements?