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Which alkali metals are less dense than water?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — alkali metal Modern version of the periodic table of the elements (printable).

Among the alkali metals, the elements that are less dense than water are lithium, sodium, and potassium.1

These three metals have densities at 20 °C of 0.534, 0.971, and 0.862 grams per cubic centimetre, respectively, all of which are lower than the density of water. In contrast, the heavier alkali metals—rubidium and cesium—have higher densities and are denser than water.1