Lithium

Lithium (from Greek
lithos 'stone') is a soft,
silver-white metal with
symbol Li and atomic
number 3. It belongs to
the alkali metal group of
chemical elements.
Under standard
conditions it is the
lightest metal and the
least dense solid
element. Like all alkali
metals, lithium is highly
reactive and flammable.
For this reason, it is
typically stored in
mineral oil. When cut
open, lithium exhibits a
metallic luster, but
contact with moist air
corrodes the surface
quickly to a dull silvery
gray, then black tarnish.
Because of its high
reactivity, lithium never
occurs freely in nature,
and instead, only appears
in compounds, which are
usually ionic . Lithium
occurs in a number of
pegmatitic minerals, but
due to its solubility as an
ion is present in ocean
water and is commonly
obtained from brines and
clays . On a commercial
scale, lithium is isolated
electrolytically from a
mixture of lithium
chloride and potassium
chloride .
The nuclei of lithium
verge on instability, since
the two stable lithium
isotopes found in nature
have among the lowest
binding energies per
nucleon of all stable
nuclides . Because of its
relative nuclear
instability, lithium is less
common in the solar
system than 25 of the
first 32 chemical
elements even though the
nuclei are very light in
atomic weight. [1] For
related reasons, lithium
has important links to
nuclear physics. The
transmutation of lithium
atoms to helium in 1932
was the first fully man-
made nuclear reaction ,
and lithium-6 deuteride
serves as a fusion fuel in
staged thermonuclear
weapons .[2]
Lithium and its
compounds have several
industrial applications,
including heat-resistant
glass and ceramics, high
strength-to-weight alloys
used in aircraft, lithium
batteries and lithium-ion
batteries. These uses
consume more than half
of lithium
production. [citation needed ]
Trace amounts of lithium
are present in all
organisms. The element
serves no apparent vital
biological function, since
animals and plants
survive in good health
without it. Nonvital
functions have not been
ruled out. The lithium
ion Li+ administered as
any of several lithium
salts has proved to be
useful as a mood-
stabilizing drug in the
treatment of bipolar
disorder , due to
neurological effects of
the ion in the human
body.
Properties
Main article: Alkali metal
Atomic and physical
Lithium pellets
covered in white
lithium hydroxide
(left) and ingots with
a thin layer of black
oxide tarnish (right)
Like the other alkali
metals , lithium has a
single valence electron
that is easily given up to
form a cation .[3]
Because of this, it is a
good conductor of heat
and electricity as well as
a highly reactive
element, though the least
reactive of the alkali
metals. Lithium's low
reactivity compared to
other alkali metals is due
to the proximity of its
valence electron to its
nucleus (the remaining
two electrons are in
lithium's 1s orbital and
are much lower in
energy, and therefore
they do not participate in
chemical bonds). [3]
Lithium metal is soft
enough to be cut with a
knife. When cut, it
possesses a silvery-white
color that quickly
changes to gray due to
oxidation. [3] 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. [4]
It is the lightest metal in
the periodic table, so
light that it can float on
water and even on oil,
and it is one of three
metals that can (the
other two are sodium
and potassium). It has a
very low density, of
approximately 0.534 g/
cm 3 , which gives sticks
of the metal a similar
heft to dowels of a
medium density wood,
such as pine. It floats on
water but also reacts
with it. [3]
Lithium floating in oil
It is the least dense of all
elements that are not
gases at room
temperature. The next
lightest element is over
60% more dense
(potassium, at 0.862 g/
cm 3 ). Furthermore, aside
from helium and
hydrogen, it is the least
dense element in a solid
or liquid state, being
only 2/3 as dense as
liquid nitrogen (0.808 g/
cm 3 ).[note 1][5]
Lithium's coefficient of
thermal expansion is
twice that of aluminium
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,
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 the most prevalent. [9]
Multiple allotropic forms
have been reported for
lithium at high pressures.
[10]
Because of its specific
heat capacity, the highest
of all solids, lithium
metal is often used in
coolants for heat
transfer applications. [11]
Chemistry and
compounds
Lithium reacts with water
easily, but with
noticeably less energy
than other alkali metals
do. The reaction forms
hydrogen gas and lithium
hydroxide in aqueous
solution. [3] Because of
its reactivity with water,
lithium is usually stored
under cover of a viscous
hydrocarbon, often
petroleum jelly . Though
the heavier alkali metals
can be stored in less
dense substances, such
as mineral oil , lithium is
not dense enough to be
fully submerged in these
liquids. [12] In moist air,
lithium rapidly tarnishes
to form a black coating
of lithium hydroxide
(LiOH and LiOH·H 2O),
lithium nitride (Li3 N) and
lithium carbonate
(Li2 CO 3 , the result of a
secondary reaction
between LiOH and CO 2 ).
[13]
Hexameric structure
of the n-butyllithium
fragment in a crystal
When placed over a
flame, lithium
compounds give off a
striking crimson color,
but when it burns
strongly the flame
becomes a brilliant
silver. Lithium will ignite
and burn in oxygen when
exposed to water or
water vapors. [14]
Lithium is flammable,
and it is potentially
explosive when exposed
to air and especially to
water, though less so
than the other alkali
metals . The lithium-water
reaction at normal
temperatures is brisk but
not violent, the hydrogen
produced will not ignite
on its own. As with all
alkali metals, lithium
fires are difficult to
extinguish, requiring dry
powder fire
extinguishers, specifically
Class D type (see Types
of extinguishing agents).
Lithium is the only metal
which reacts with
nitrogen under normal
conditions.[15][16]
Lithium has a diagonal
relationship with
magnesium , an element
of similar atomic and
ionic radius . Chemical
resemblances between
the two metals include
the formation of a
nitride by reaction with
N 2 , the formation of an
oxide (Li2 O) and
peroxide (Li 2 O 2) when
burnt in O 2 , salts with
similar solubilities , and
thermal instability of the
carbonates and nitrides.
[13][17] The metal reacts
with hydrogen gas at
high temperatures to
produce lithium hydride
(LiH). [18]
Other known binary
compounds include the
halides ( LiF , LiCl, LiBr ,
LiI ), and the sulfide (Li2 S
), the superoxide ( LiO 2),
carbide (Li2 C 2 ). Many
other inorganic
compounds are known,
where lithium combines
with anions to form
various salts: borates,
amides, carbonate ,
nitrate , or borohydride
(LiBH 4 ). Multiple
organolithium reagents
are known where there is
a direct bond between
carbon and lithium atoms
effectively creating a
carbanion . These are
extremely powerful bases
and nucleophiles. In
many of these
organolithium
compounds, the lithium
ions tend to aggregate
into high-symmetry
clusters by themselves,
which is relatively
common for alkali
cations. [19]
Isotopes
Main article: Isotopes of
lithium
Naturally occurring
lithium is composed of
two stable isotopes , 6 Li
and 7Li, the latter being
the more abundant
(92.5% natural
abundance). [3][12][20]
Both natural isotopes
have anomalously low
nuclear binding energy
per nucleon compared to
the next lighter and
heavier elements, helium
and beryllium, which
means that alone among
stable light elements,
lithium can produce net
energy through nuclear
fission . The two lithium
nuclei have lower binding
energies per nucleon
than any other stable
nuclides other than
deuterium and helium-3 .
[21] As a result of this,
though very light in
atomic weight, lithium is
less common in the solar
system than 25 of the
first 32 chemical
elements. [1] Seven
radioisotopes have been
characterized, the most
stable being 8 Li with a
half-life of 838 ms and
9 Li with a half-life of
178 ms. All of the
remaining radioactive
isotopes have half-lives
that are shorter than
8.6 ms. The shortest-
lived isotope of lithium is
4 Li, which decays
through proton emission
and has a half-life of 7.6
× 10 −23 s. [22]
7 Li is one of the
primordial elements (or,
more properly,
primordial nuclides)
produced in Big Bang
nucleosynthesis. A small
amount of both 6Li and
7 Li are produced in
stars, but are thought to
be burned as fast as
produced. [23] Additional
small amounts of lithium
of both 6 Li and