# The modern periodic table lists all the elements in order of what?

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The modern Periodic Table uses $\text{atomic number}$, $Z$, as the defining criterion. And $Z$ specifies the number of protons, massive, positively charged particles, present in the nucleus. $Z = 1$, the element is hydrogen; $Z = 2$, the element is helium; $Z = 3$, the element is lithium;...................$Z = 22$, the element is titanium.