What is the smallest unit of an element that retains its chemical properties?

The atom is the fundamental building block of matter and the smallest unit of an an element that still retains the characteristic chemical properties of that element. Atoms consist of a nucleus containing protons and neutrons, surrounded by a cloud of electrons. While atoms can combine to form molecules and compounds, it is the individual atom that defines the element. For instance, a gold atom is what makes gold gold; if you were to break down a gold atom further, it would no longer be gold. Molecules are formed by the chemical bonding of two or more atoms, and compounds are formed when atoms of two or more different elements chemically combine. Ions are atoms or molecules that have gained or lost electrons, acquiring an electrical charge.