Each period of the periodic table begins with an element from which family?

Periods of the periodic table are the horizontal rows. Families, which are also called groups, are the vertical columns. Properties of elements increase or decrease moving across a period and tend to be similar within a family.

Each period begins with an element in Group 1, called the alkali metals.

The alkali metals are lithium, sodium, potassium, rubidium, cesium and francium. They share the properties of being soft, malleable solids with low densities and low melting points compared to other metallic elements. They react violently with water to produce hydrogen gas and hydroxide ion, a base. Reactivity of the alkali metals increases going down the group, and as a group they're the most reactive of the metals. The alkali metals have one valence electron which is lost in chemical reactions, forming a 1+ ion. The results in ionic compounds such as NaCl, LiF and K2O.