How many elements are metalloids? How many are nonmetals?

Some elements do not fit neatly into metal or nonmetal categories and have properties of both. These elements are called metalloids. They include boron, silicon, germanium, arsenic, antimony, tellurium, and polonium. On the periodic table, these elements are placed directly next to the dividing line between metals and nonmetals.

In some cases, atoms of an element might be slightly different. They might weigh different amounts. How does this happen if all the atoms of an element have the same number of protons? Remember the neutrons in the atom’s nucleus? While the number of protons cannot change, atoms of the same element can have a different number of neutrons. When this happens, the atom’s atomic mass is changed. Atoms of the same element with different atomic masses are called isotopes.