What is Lithium?
{{Infobox lithium}} '''Lithium''' (from Greek ''lithos'' 'stone') is a soft, silver-white [[metal]] with [[Chemical symbol|symbol]]&nbsp;'''Li'''. It is the third [[chemical element]] in the [[periodic table]]. This means that it has 3 [[proton]]s in its nucleus and 3 [[electron]]s around it. Its [[atomic number]] is 3. Its [[mass number]] is 6.94. It has two common [[isotope]]s, <sup>6</sup>Li and <sup>7</sup>Li. <sup>7</sup>Li is more common; 92.5% of lithium is <sup>7</sup>Li. Lithium is a soft silvery metal that is very [[wikt:reactive|reactive]]. It is used in lithium batteries and certain medicines. ==Properties== ===Physical properties=== Lithium is one of the [[alkali metal]]s. Lithium is a silvery solid [[metal]] (when freshly cut). It is very soft. Thus it can be cut easily with a knife. It melts at a low temperature. It is very light, similar to wood. It is the least dense metal and the least dense element in a solid or liquid state. It can hold more heat than any other solid element. It conducts heat and [[electricity]] easily. ===Chemical properties=== It will [[Chemical reaction|react]] with [[water]], giving off [[hydrogen]] to form a [[base (chemistry)|basic]] solution ([[lithium hydroxide]]). Because of this, lithium must be stored in petroleum jelly. Sodium and [[potassium]] can be stored in oil but lithium cannot because it is so light. It will just float on the oil and not be protected by it. Lithium also reacts with [[halogen]]s. It can react with [[nitrogen]] gas to make [[lithium nitride]]. It reacts with air to make a black [[tarnish]] and then a white powder of [[lithium hydroxide]] and [[lithium carbonate]]. ===Chemical compounds=== :''{{See also cat|Lithium compounds}}'' [[File:FlammenfärbungLi.png|thumb|Flame test for lithium]] Lithium forms [[chemical compound]]s with only one [[oxidation state]]: +1. Most of them are white and unreactive. They make a bright red color when heated in a flame. They are a little toxic. Most of them dissolve in water. Lithium carbonate is less soluble