Lithium

Lithium is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the lightest metal and the lightest solid element, being able to float on water. Like all alkali metals, lithium is highly reactive and flammable, and must be stored in mineral oil. When cut, it exhibits a metallic luster, but moist air corrodes it quickly to a dull silvery grey, (Unlike the other alkali metals, solid Li it does not catch fire when it comes into contact with water⁽¹⁾. A lithium metal surface exposed to air develops a black tarnish, which seems odd since Li₂O, LiOH, or LiCO₃. That tarnish is Li₃N. Although its reaction with oxygen is stronger, lithium reacts quickly with atmospheric nitrogen (the nitride layer does not passivate the metal.) It never occurs freely in nature, but only in ionic compounds such as pegmatitic minerals, which were once the main source of lithium. Due to its solubility as an ion, it is present in ocean water and is commonly obtained from brines. Lithium metal is isolated electrolytically from a mixture of lithium chloride and potassium chloride.

Lithium has two stable isotopes, ⁶Li and ⁷Li. Neither can form in stars. The element, in fact, is consumed in the cores of young stars. The absence of lithium in its spectrum is a good way to distinguish a low-mass star from a brown dwarf. Instead, lithium usually forms in space as a result of cosmic-ray collisions.

The concept of "lithium isotope" is a bit confused, even by the professionals⁽³⁾. Technically speaking, something cannot be isotope of an element unless it can acquire electrons and act like an atom (ion). Two particles ⁴Li and ⁵Li, are special cases. Both are produced as side reactions in the proton-proton sequence of reactions that powers the sun. Other 3-proton particles; ³Li, ¹⁰Li, ¹²Li, ¹³Li, ...; might form a few times during the life of the univese - but they are so unlikely that they may be ignored. Lithium isotopes are summarized in the table below.

Lithium isotope decay

Name	Li4	Li5	Li6	Li7	Li8	Li9	Li10	Li11	Li12
Decay	$\ce{Li4->[{91ys}][{p}]He3}$	$\ce{Li5->[{370ys}][{p}]He4}$	Stable	Stable	$\ce{Li8->[{838ms}][{B-}]Be8->[{81.9as}][{a}]He4}$	$\ce{Li9->[{0.1s}][{B-}]Be9}$	$\ce{Li10->[{2zs}][{n}]Li9->[{0.1s}][{N}]Be9}$	$\ce{Li11->[{0.8s}][{B-}]Be11->[{13s}][{B-}]B11}$	$\ce{^{12}_{3}Li->[{10ns}][{N}]Li11->[{0.8s}][{B-}]Be11->[{13s}][{B-}]B11}$

Note that ⁹Li and ¹¹Li have multiple decay modes, which could not be described in the table. That's a pity because ¹¹Li has seven observed decay modes.

The transmutation of lithium atoms to helium in 1932 was the first fully man-made nuclear reaction, and lithium deuteride serves as a fusion fuel in staged thermonuclear weapons.

Lithium and its compounds have several industrial applications, including heat-resistant glass and ceramics, lithium grease lubricants, flux additives for iron, steel and aluminium production, lithium batteries, and lithium-ion batteries. These uses consume more than three quarters of lithium production.

Lithium was used as fuel in the world's first liquid-metal fueled engine. This was the ALWT (later MK 50) torpedo engine, which used the 8 Li + SF₆ --> 6 LiF + Li₂S reaction to generate heat to drive a steam turbine^(1),(2).

Lithium is present in biological systems in trace amounts; its functions are uncertain. Lithium salts have proven to be useful as a mood-stabilizing drug in the treatment of bipolar disorder in humans.

References

1. first-hand experience
2. Mark 50 torpedo, Wikipedia
3. "Isotopes o Lithium", Wikipedia

Lithium
3Li
H ↑ Li ↓ Na Periodic table helium ← lithium → beryllium
Appearance
silvery-white (shown floating in oil)
Spectral lines of lithium
General properties
Name, symbol, number	lithium, Li, 3
Pronunciation	/ˈlɪθiəm/ LI-thee-əm
Element category	alkali metal
Group, period, block	1, 2, s
Standard atomic weight	6.94(1)
Electron configuration	[He] 2s1 2, 1
History
Discovery	Johan August Arfwedson (1817)
First isolation	William Thomas Brande (1821)
Physical properties
Phase	solid
Density (near r.t.	0.534 g·cm−3
Liquid density at m.p.	0.512 g·cm−3
Melting point	453.69 K, 180.54 °C, 356.97 °F
Boiling point	1615 K, 1342 °C, 2448 °F
Critical point	(extrapolated) 3223 K, 67 MPa
Heat of fusion	3.00 kJ·mol−1
Heat of vaporization	147.1 kJ·mol−1
Molar heat capacity	24.860 J·mol−1·K−1
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 797 885 995 1144 1337 1610
Atomic properties
Oxidation states	+1 (strongly basic oxide)
Electronegativity	0.98 (Pauling scale)
Ionization energies	1st: 520.2 kJ·mol−1 2nd: 7298.1 kJ·mol−1 3rd: 11815.0 kJ·mol−1
Atomic radius	152 pm
Covalent radius	128±7 pm
Crystal structure	body-centered cubic
Magnetic ordering	paramagnetic
Electrical resistivity	(20 °C) 92.8 nΩ·m
Thermal conductivity	84.8 W·m−1·K−1
Thermal expansion	(25 °C) 46 µm·m−1·K−1
Speed of sound (thin rod)	(20 °C) 6000 m·s−1
Young's modulus	4.9 GPa
Shear modulus	4.2 GPa
Bulk modulus	11 GPa
Mohs hardness	0.6
CAS registry number	7439-93-2
Most stable isotopes
Main article: Isotopes of lithium
iso NA half-life DM DE (MeV) DP 6Li 7.5% 6Li is stable with 3 neutrons 7Li 92.5% 7Li is stable with 4 neutrons 6Li content may be as low as 3.75% in natural samples. 7Li would therefore have a content of up to 96.25%.
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9-Period Periodic Table of Elements
1	1 H																																																																	2 He
2	3 Li	4 Be																																																																	5 B	6 C	7 N	8 O	9 F	10 Ne
3	11 Na	12 Mg																																																																	13 Al	14 Si	15 P	16 S	17 Cl	18 Ar
4	19 K	20 Ca																																																																	21 Sc	22 Ti	23 V	24 Cr	25 Mn	26 Fe	27 Co	28 Ni	29 Cu	30 Zn	31 Ga	32 Ge	33 As	34 Se	35 Br	36 Kr
5	37 Rb	38 Sr																																																																	39 Y	40 Zr	41 Nb	42 Mo	43 Tc	44 Ru	45 Rh	46 Pd	47 Ag	48 Cd	49 In	50 Sn	51 Sb	52 Te	53 I	54 Xe
6	55 Cs	56 Ba																																																					57 La	58 Ce	59 Pr	60 Nd	61 Pm	62 Sm	63 Eu	64 Gd	65 Tb	66 Dy	67 Ho	68 Er	69 Tm	70 Yb	71 Lu	72 Hf	73 Ta	74 W	75 Re	76 Os	77 Ir	78 Pt	79 Au	80 Hg	81 Tl	82 Pb	83 Bi	84 Po	85 At	86 Rn
7	87 Fr	88 Ra																																																					89 Ac	90 Th	91 Pa	92 U	93 Np	94 Pu	95 Am	96 Cm	97 Bk	98 Cf	99 Es	100 Fm	101 Md	102 No	103 Lr	104 Rf	105 Db	106 Sg	107 Bh	108 Hs	109 Mt	110 Ds	111 Rg	112 Cn	113 Nh	114 Fl	115 Mc	116 Lv	117 Ts	118 Og
8	119 Uue	120 Ubn																															121 Ubu	122 Ubb	123 Ubt	124 Ubq	125 Ubp	126 Ubh	127 Ubs	128 Ubo	129 Ube	130 Utn	131 Utu	132 Utb	133 Utt	134 Utq	135 Utp	136 Uth	137 Uts	138 Uto	139 Ute	140 Uqn	141 Uqu	142 Uqb	143 Uqt	144 Uqq	145 Uqp	146 Uqh	147 Uqs	148 Uqo	149 Uqe	150 Upn	151 Upu	152 Upb	153 Upt	154 Upq	155 Upp	156 Uph	157 Ups	158 Upo	159 Upe	160 Uhn	161 Uhu	162 Uhb	163 Uht	164 Uhq	165 Uhp	166 Uhh	167 Uhs	168 Uho	169 Uhe	170 Usn	171 Usu	172 Usb
9	173 Ust	174 Usq
Alkali metal Alkaline earth metal Lanthanide Actinide Superactinide Transition metal Post-transition metal Metalloid Other nonmetal Halogen Noble gas predicted predicted predicted predicted predicted predicted predicted predicted predicted