Magnesium
Atomic number 12 means that every Magnesium nucleus contains 12 protons. That proton count is the element's identity: change it and you no longer have Magnesium.
Start with the nucleus
Atomic number 12 means that every Magnesium nucleus contains 12 protons. That proton count is the element's identity: change it and you no longer have Magnesium.
Magnesium (Mg) is chemical element 12. It belongs to the alkaline-earth metals, and its reference state at room temperature is a solid. Those basic facts are a useful starting point for its chemistry and applications.
In practice, it turns up most often in alloys, fireworks and biology.
See the atom
Conceptual visual: electron shells are a learning aid, not a literal picture of quantum orbitals.
What this number means
Atomic number 12 means that every Magnesium nucleus contains 12 protons. That proton count is the element's identity: change it and you no longer have Magnesium.