Atomic number
Match each element with its atomic number.
An element's atomic number is the count of protons in its nucleus, and it also fixes its position on the periodic table. Hydrogen is 1, carbon is 6, iron is 26, gold is 79, uranium is 92, and oganesson closes the table at 118. This quiz tests both directions: pick the element from its number, or recall the number from a name.
How many questions?
Frequently asked questions
What does atomic number actually measure?
It's the number of protons in an atom's nucleus. Because a neutral atom has the same number of electrons as protons, the atomic number also fixes the electron count and the element's chemical behaviour.
Does atomic number change between isotopes?
No. Isotopes of the same element have the same number of protons (same atomic number) but different numbers of neutrons, which changes the atomic mass.
How is atomic number different from atomic mass?
Atomic number counts only protons. Atomic mass is the average mass of an atom in atomic mass units (u), which depends on protons, neutrons, and the natural abundance of isotopes.
Why is the atomic number written as a subscript?
By convention it sits as a subscript to the left of the symbol. When the mass number is also shown it goes as a superscript on the same side, so a full label looks like 12-superscript C 6-subscript.
What's the largest atomic number that exists?
Oganesson with atomic number 118 is the heaviest officially named element. Heavier candidates (119, 120, and beyond) have been theorised and partially synthesised but are not confirmed on the periodic table yet.