Like other alkali metals, lithium has a single valence electron that is easily given up to form a cation. For this reason it is a good conductor of heat and electricity as well as a highly reactive element, although it is the least reactive of the alkali metals. The low reactivity of lithium compared to other alkali metals is due to the proximity of its valence electron to the nucleus (the remaining two electrons are located in the 1s orbital of lithium and have a much lower energy, and therefore do not participate in chemical bonds ).Lithium metal is soft enough to be cut with a knife. When cut it has a silvery-white color which quickly turns gray due to oxidation. Although it has one of the lowest melting points of all metals (180°C), it has the highest melting and boiling points of the alkali metals. Lithium has a very low density of 0.534 g/cm3, comparable to that of pine wood. It is the least dense of all solid elements at room temperature, the next lightest solid element (potassium, at 0.862 g/cm3) being more than 60% denser. Furthermore, other than helium and hydrogen, it is less dense than any liquid element, being only 2/3 as dense as liquid nitrogen (0.808 g/cm3).[note 1][5] Lithium can float on lighter hydrocarbon oils and is one of only three metals that can float on water, the other two being sodium and potassium. Lithium floats in oil The thermal expansion coefficient of lithium is twice that of aluminum and almost four times that of iron.[6] It has the highest specific heat capacity of any solid element. Lithium is superconductive below 400 μK at standard pressure[7] and at higher temperatures (more than 9 K) at very high pressures (>20 GPa)[8] At temperatures below 70 K, lithium, like sodium, it's under... .. half the paper... er than they should be, and some younger stars have much more. Lithium deficiency in older stars is apparently caused by "mixing" of lithium into the interior of stars, where it is destroyed. Additionally, lithium is produced in younger stars. Although it transmutes into two helium atoms upon collision with a proton at temperatures above 2.4 million degrees Celsius (most stars easily reach this temperature inside them), lithium is more abundant than expected in next generation stars, for causes not yet fully understood. Although it was one of the first three elements (along with helium and hydrogen) to be synthesized in the Big Bang, lithium, along with beryllium and boron, are markedly less abundant than other nearby elements. This is a result of the low temperature needed to destroy lithium and the lack of common processes to produce it.[34]