| A metal in the first column of the periodic table (i.e., lithium, sodium, potassium, rubidium, caesium and francium). With the exception of francium, these metals are all soft and silvery.
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| They may be readily fused and volatilized with their melting and boiling points becoming lower with increasing atomic mass. They are the strongest electropositive metals. These elements react vigorously, even violently with water.
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| The alkali metals are silver-colored (caesium has a golden tinge), soft, low-density metals, which react readily with halogens to form ionic salts, and with water to form strongly alkaline (basic) hydroxides. These elements all have one electron in
their outermost shell, so the energetically preferred state of achieving a filled electron shell is to lose one electron to
form a singly charged positive ion, or cation.
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| Hydrogen, with a solitary electron, is usually placed at the top of Group 1 of the periodic table, but it is not considered an alkali metal; rather it exists naturally as a diatomic gas. Removal of its single electron requires
considerably more energy than removal of the outer electron for the alkali metals. As in the halogens, only one additional electron is required to fill in the outermost shell of the hydrogen atom, so hydrogen can in some circumstances behave like a halogen, forming the negative hydride ion. Binary compounds of hydride with the alkali metals and some transition metals have been prepared. Under extremely high pressure,
such as is found at the core of Jupiter, hydrogen does become metallic and behaves like an alkali metal
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