Alkali metal

An alkali metal is a metallic element in Group 1 of the periodic table, excluding hydrogen. These elements readily lose one electron and form compounds that often produce alkaline solutions.

Valence electron: An electron in an atom’s outermost occupied shell that can participate in chemical bonding. Each alkali metal has one outer-shell electron, which it readily loses.
Atomic number: The number of protons in an atom’s nucleus, which defines the chemical element. Atomic number distinguishes the successive elements in the alkali-metal group.
Lithium-ion battery: A rechargeable battery that moves lithium ions between electrodes during charging and discharging. Lithium’s low mass and electrochemical properties make it useful in portable energy storage.
Alkaline earth metal: A Group 2 metallic element whose atoms typically lose two electrons to form divalent ions. Group 2 metals have two outer electrons and generally react less vigorously with water.
Lithium: The lightest alkali metal, used in batteries, ceramics, and some medicines. Lithium is the smallest and least dense member of the group.
First ionization energy: The energy required to remove one electron from a neutral atom in the gas phase. Its low value makes formation of singly charged alkali-metal ions favorable.
Electron shell: A region of an atom associated with electrons of similar principal energy level. Moving down Group 1 adds an occupied shell while preserving one outer electron.
Sodium-vapor lamp: A gas-discharge lamp that produces light by exciting sodium vapor. Sodium’s strong yellow emission gives these lamps their characteristic light.
Transition metal: An element whose atom has a partially filled d subshell or forms cations with an incomplete d subshell. Transition metals often have variable oxidation states, unlike the usual +1 state of alkali metals.
Sodium: A soft, reactive alkali metal abundant in seawater and many minerals. Sodium is a familiar example whose compounds are widespread in food and industry.

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