The number of protons in an atom of an element is equal to the atomic number of that element. The atomic number of an element is a unique identifier for that element and is used to determine its position on the periodic table. For example, the atomic number of hydrogen is 1, meaning that a hydrogen atom has 1 proton in its nucleus. The atomic number of helium is 2, meaning that a helium atom has 2 protons in its nucleus, and so on.