The element boron belongs to the earth metal family of elements, which is also called the boron group. In addition to boron, this family includes aluminum, gallium, indium, thallium and ununtrium. Families consists of groups of elements with similar properties.
Another term for the earth metal family is group 13. All of the elements in the group have three valence electrons and have properties that place them between metals and nonmetals. Officially, boron is classified as a semi-metal, and the rest of the group are classified as metals. Ununtrium is a man-made radioactive element that has not been widely studied. Scientists classify it in the boron group because of its close relationship with thallium.