Chemistry of Lithium
Lithium is a rare element found primarily in molten rock and saltwater in very small amounts. It is understood to be non-vital in human biological processes, although it is used in many drug treatments due to its positive effects on the human brain. Because of its reactive properties, humans have utilized lithium in batteries, nuclear fusion reactions, and thermonuclear weapons.
Lithium's identification first came when it was found to be a part of the mineral Petalite. It was discovered by chemist Yohan August Arfwedson when he was analyzing the Petalite ore. Lithium is on the first column of the Periodic Table, thus making Lithium an alkali metal with the atomic number = 3 and an atomic mass of 6.941 g/mol. This means that Lithium has 3 protons, 3 electrons and 4 neutrons (6.941 - 3 = ~4). Being an alkali metal, Lithium is a soft, flammable, and highly reactive metal that tends to form hydroxides. It also has a pretty low density. When Lithium is in standard conditions, it is the least dense solid element.
Figure 1. Lithium atom.
Table 1. Properties of lithium.
Periodic Trends of Lithium
Being on the upper left side of the Periodic Table, Lithium has a fairly low electronegativity and electron affinity as compared to the rest of the elements. Also, Lithium has high metallic character and subsequently lower nonmetallic character when compared with the other elements. Lithium has a higher atomic radius than most of the elements on the Periodic Table.
Lithium (Table 1) is part of the Group 1 Alkali Metals, which are highly reactive and are never found in their pure form in nature. This is due to their electron configuration, in that they have a single valence electron (Figure 1) which is very easily given up in order to create bonds and form compounds.
_↑ ↓_ _↑__
Reactions with Water
When placed in contact with water, pure lithium reacts to form lithium hydroxide and hydrogen gas.
2Li(s) + 2H2O(l) → 2LiOH(aq) + H2(g)
Out of all the group 1 metals, lithium reacts the least violently, slowly releasing the hydrogen gas which may create a bright orange flame only if a substantial amount of lithium is used. This occurs because lithium has the highest activation energy of its group - that is, it takes more energy to remove lithium's one valence electron than with other group 1 elements, because lithium's electron is closer to its nucleus. Atoms with higher activation energies will react slower, although lithium will release more total heat through the entire process.
Reactions with Air
Pure lithium will form lithium hydroxide due to moisture in the air, as well as lithium nitride (Li3N) from N2 gas, and lithium carbonate (Li2CO3) from carbon dioxide. These compounds give the normally the silver-white metal a black tarnish. Additionally, it will combust with oxygen as a red flame to form lithium oxide.
4Li(s) + O2(g) → 2Li2O
Lithium is able to be used in the function of a Lithium battery in which the Lithium metal serves as the anode. Lithium ions serve in lithium ion batteries (chargeable) in which the lithium ions move from the negative to positive electrode when discharging, and vice versa when charging.
Lithium has the highest specific heat capacity of the solids, Lithium tends to be used as a cooler for heat transfer techniques and applications.
Sources and Extraction
Lithium is most commonly found combined with aluminum, silicon, and oxygen to form the minerals known as spodumene (LiAl(SiO3)2) or petalite/castorite (LiAlSi4O10). These have been found on each of the 6 inhabited continents, but they are mined primarily in Western Australia, China, and Chile. Mineral sources of lithium are becoming less essential, as methods have now been developed to make use of the lithium salts found in saltwater.
Extraction from minerals
The mineral forms of lithium are heated to a high enough temperature (1200K - 1300K) in order to crumble them and thus allow for subsequent reactions to more easily take place. After this process, one of three methods can be applied.
The lithium chloride obtained from any of the three methods undergoes an oxidation-reduction reaction in an electrolytic cell, in order to separate the chloride ions from the lithium ions. The chloride ions are oxidized, and the lithium ions are reduced.
2Cl - 2e- → Cl2 (oxidation)
Li+ + e- → Li (reduction)
Extraction from Saltwater
Saltwater naturally contains lithium chloride, which must be extracted in the form of lithium carbonate, then it is re-treated, separated into its ions, and reduced in the same electrolytic process as in extraction from lithium ores. Only three saltwater lakes in the world are currently used for lithium extraction, in Nevada, Chile, and Argentina.
Saltwater is channeled into shallow ponds and over a period of a year or more, water evaporates out to leave behind various salts. Lime is used to remove the magnesium salt, so that the remaining solution contains a fairly concentrated amount of lithium chloride. The solution is then treated with sodium carbonate in order for usable lithium carbonate to precipitate out.
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