The atomic number on the periodic table represents the number of protons in the nucleus of each atom of that element.

Quick Scoop

  • The atomic number is the count of protons in the nucleus of an atom.
  • It defines which element you have: if an atom has 6 protons (atomic number 6), it is carbon; if it has 8 protons (atomic number 8), it is oxygen.
  • On a typical periodic table square, the atomic number is the small whole number written above the element symbol.
  • In a neutral atom, the atomic number also tells you the number of electrons, because protons’ positive charges are balanced by an equal number of negatively charged electrons.

Think of the atomic number like an element’s “ID number” – change the number of protons, and you’re no longer talking about the same element at all.

TL;DR: The atomic number tells you how many protons are in the nucleus, which uniquely identifies the element and sets its basic chemical behavior.

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