What is a family on the periodic table?

What is a family on the periodic table? A family on the periodic table is a set of elements, arranged together, that share similar chemical and physical properties, usually because they have the same number of valence electrons.

Many families are single groups (vertical columns): the alkali metals (group 1), alkaline earth metals (group 2), halogens (group 17) and noble gases (group 18). Others span several columns, such as the transition metals in groups 3 to 12, or sit outside the main body, such as the lanthanides and actinides. Readers also ask “how to read a periodic table”, which has its own short answer.

This site shows ten families: alkali metals, alkaline earth metals, transition metals, post-transition metals, metalloids, reactive nonmetals, halogens, noble gases, lanthanides and actinides. Textbooks vary on names and borders, for example whether hydrogen belongs with the alkali metals or whether lanthanides and actinides count as transition metals. 'Family' and 'group' are often used interchangeably, but a group is strictly a numbered column, while a family is defined by shared behavior.

The most familiar families have their own behaviors. Alkali metals (lithium, sodium, potassium, rubidium, cesium and francium) are soft, shiny and react vigorously with water. Another common question on this site is “why is it called a periodic table”.

Alkaline earth metals (beryllium to radium) are harder and less reactive. Transition metals such as iron, copper, nickel and gold form colored compounds and often have several oxidation states.

Halogens (fluorine, chlorine, bromine, iodine, astatine and tennessine) are reactive nonmetals that form salts with metals, and noble gases are almost completely unreactive. Lanthanides and actinides are the two f-block rows, the first used in magnets and lasers and the second including radioactive uranium and plutonium. The same series of answers also covers “is water in the periodic table”.

Metalloids such as silicon and arsenic sit between metals and nonmetals, and post-transition metals such as aluminium, tin and lead fill the area to the right of the transition metals. Knowing the family tells you how an element will probably react, what its compounds look like and which other elements it resembles. Tables usually indicate each family with a different color.