What is the atomic number of gold?

The atomic number of gold is 79.

An element’s atomic number is the number of protons in the nucleus of each of its atoms. Every gold atom therefore has 79 protons. If the atom is electrically neutral, it also has 79 electrons, although it can gain or lose electrons to form ions without changing into a different element.

Gold’s chemical symbol is Au, from the Latin word aurum. On the periodic table it is a group 11 transition metal, alongside copper and silver. Its atomic number identifies it more fundamentally than its colour, value, or physical appearance: an atom with 78 protons is platinum, while one with 80 protons is mercury.

The number 79 is not gold’s atomic mass. Naturally occurring gold is overwhelmingly the isotope gold-197, and its standard relative atomic mass is about 196.97. Atomic number counts protons; atomic mass reflects the combined mass of protons and neutrons. This distinction is a common source of confusion in basic chemistry questions.