# What is atomic number of gold?

For $A u$, $Z = 79$
What does this mean? It means that in the gold nucleus there are 79 protons, 79 positively charged, massive particles. If there were a different number then the element would NOT be gold, because the atomic number defines elemental indentity: $Z = 1$, $H$; $Z = 2$, $H e$; ..........$Z = 78$, $P t$, $Z = 79$, $A u$