<P> Like the other alkali metals, lithium has a single valence electron that is easily given up to form a cation . Because of this, lithium is a good conductor of heat and electricity as well as a highly reactive element, though it is the least reactive of the alkali metals . Lithium's low reactivity is due to the proximity of its valence electron to its nucleus (the remaining two electrons are in the 1s orbital, much lower in energy, and do not participate in chemical bonds). </P> <P> Lithium metal is soft enough to be cut with a knife . When cut, it possesses a silvery - white color that quickly changes to gray as it oxidizes to lithium oxide . While it has one of the lowest melting points among all metals (180 ° C), it has the highest melting and boiling points of the alkali metals . </P> <P> Lithium has a very low density (0.534 g / cm), comparable with pine wood . It is the least dense of all elements that are solids at room temperature; the next lightest solid element (potassium, at 0.862 g / cm) is more than 60% denser . Furthermore, apart from helium and hydrogen, it is less dense than any liquid element, being only two thirds as dense as liquid nitrogen (0.808 g / cm). Lithium can float on the lightest hydrocarbon oils and is one of only three metals that can float on water, the other two being sodium and potassium . </P> <P> Lithium's coefficient of thermal expansion is twice that of aluminium and almost four times that of iron . Lithium is superconductive below 400 μK at standard pressure and at higher temperatures (more than 9 K) at very high pressures (> 20 GPa). At temperatures below 70 K, lithium, like sodium, undergoes diffusionless phase change transformations . At 4.2 K it has a rhombohedral crystal system (with a nine - layer repeat spacing); at higher temperatures it transforms to face - centered cubic and then body - centered cubic . At liquid - helium temperatures (4 K) the rhombohedral structure is prevalent . Multiple allotropic forms have been identified for lithium at high pressures . </P>

Is lithium a solid liquid or gas at room temp