An alkali metal is an element in Group 1 of the periodic table, with one valence electron; the alkali metals are soft, reactive metals that form alkaline hydroxides with water.
An alkali metal is an element in Group 1 of the periodic table, with one valence electron; the alkali metals are soft, reactive metals that form alkaline hydroxides with water. Malay: logam alkali · Chinese: 碱金属.
Lithium, sodium and potassium are the alkali metals you study most. Each has a single electron in its outermost shell, so each reacts by losing that one electron to form an ion with a charge of +1, such as Na⁺. They are soft enough to cut with a knife, they have low densities, and they are so reactive that they are stored under oil to keep them away from air and water. The name “alkali” comes from the alkaline solution they make when they react with water.
Example. When sodium is added to water it reacts vigorously, moving across the surface and giving off hydrogen gas, and the solution left behind is sodium hydroxide, which is alkaline and turns red litmus blue. Going down the group the reaction becomes more violent, potassium reacts faster and more fiercely than sodium, which reacts faster than lithium, because the outer electron is held more loosely in the larger atom.
Confusion to avoid. Do not confuse the alkali metals of Group 1 with the alkaline earth metals of Group 2, and do not confuse “alkali metal” (an element) with “alkali” (a soluble base in solution). The reactivity trend also runs the opposite way to the halogens: alkali metals become more reactive down the group, halogens less reactive.
In the Periodic Table of Elements chapter the alkali metals are the model for how a whole group shares properties, and their reactivity trend is explained directly by atomic size and how easily the single valence electron is lost.
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