In
chemistry, the term chemically inert is used to describe a substance that is not
chemically reactive. From a thermodynamic perspective, a substance is inert, or
nonlabile, if it is thermodynamically
unstable
In numerous fields of study, the component of instability within a system is generally characterized by some of the outputs or internal states growing without bounds. Not all systems that are not stable are unstable; systems can also be mar ...
(positive
standard Gibbs free energy of formation) yet decomposes at a slow, or negligible rate.
Most of the
noble gases
The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low ch ...
, which appear in the last column of the
periodic table, are classified as inert (or unreactive). These elements are stable in their naturally occurring form (gaseous form) and they are called
inert gases
An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. The noble gases often do not react with many substances and were historically referred to ...
.
Noble gas
The noble gases (
helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
,
neon,
argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as ...
,
krypton
Krypton (from grc, κρυπτός, translit=kryptos 'the hidden one') is a chemical element with the symbol Kr and atomic number 36. It is a colorless, odorless, tasteless noble gas that occurs in trace amounts in the atmosphere and is often ...
,
xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
and
radon
Radon is a chemical element with the symbol Rn and atomic number 86. It is a radioactive, colourless, odourless, tasteless noble gas. It occurs naturally in minute quantities as an intermediate step in the normal radioactive decay chains through ...
) were previously known as 'inert gases' because of their perceived lack of participation in any chemical reactions. The reason for this is that their outermost
electron shell
In chemistry and atomic physics, an electron shell may be thought of as an orbit followed by electrons around an atom's nucleus. The closest shell to the nucleus is called the "1 shell" (also called the "K shell"), followed by the "2 shell" (or ...
s (valence shells) are completely filled, so that they have little tendency to gain or lose electrons. They are said to acquire a
noble gas configuration, or a full
electron configuration.
It is now known that most of these gases in fact ''do'' react to form
chemical compounds
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
, such as
xenon tetrafluoride
Xenon tetrafluoride is a chemical compound with chemical formula . It was the first discovered binary compound of a noble gas. It is produced by the chemical reaction of xenon with fluorine:
: Xe + 2 →
This reaction is exothermic, rele ...
. Hence, they have been renamed to 'noble gases', as the only two of these we know truly to be inert are helium and neon. However, a large amount of energy is required to drive such reactions, usually in the form of heat, pressure, or radiation, often assisted by
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
s. The resulting compounds often need to be kept in moisture-free conditions at low temperatures to prevent rapid decomposition back into their elements.
Inert gas
The term ''inert'' may also be applied in a relative sense. For example, molecular
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
is an
inert gas
An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. The noble gases often do not react with many substances and were historically referred to ...
under ordinary conditions, existing as
diatomic molecule
Diatomic molecules () are molecules composed of only two atoms, of the same or different chemical elements. If a diatomic molecule consists of two atoms of the same element, such as hydrogen () or oxygen (), then it is said to be homonuclear. O ...
s, . The presence of a strong triple
covalent bond in the molecule renders it unreactive under normal circumstances. Nevertheless, nitrogen gas does react with the
alkali metal lithium
Lithium (from el, λίθος, lithos, lit=stone) 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 least dense metal and the least dense solid ...
to form compound
lithium nitride
Lithium nitride is a compound with the formula Li3N. It is the only stable alkali metal nitride. The solid has a reddish-pink color and high melting point.
Preparation and handling
Lithium nitride is prepared by direct combination of elemental ...
(Li
3N), even under ordinary conditions. Under high pressures and temperatures and with the right catalysts, nitrogen becomes more reactive; the
Haber process
The Haber process, also called the Haber–Bosch process, is an artificial nitrogen fixation process and is the main industrial procedure for the production of ammonia today. It is named after its inventors, the German chemists Fritz Haber and ...
uses such conditions to produce
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
from atmospheric nitrogen.
Main uses
Inert atmospheres consisting of gases such as
argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as ...
,
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
, or
helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
are commonly used in chemical reaction chambers and in storage containers for
oxygen- or
water-sensitive substances, to prevent unwanted reactions of these substances with oxygen or water.
Argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as ...
is widely used in
fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...
tubes and low energy light bulbs. Argon gas helps to protect the metal filament inside the bulb from reacting with oxygen and
corroding the filament under high temperature.
Neon is used in making advertising signs. Neon gas in a vacuum tube glows bright red in colour when electricity is passed through. Different coloured neon lights can also be made by using other gases.
Helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
gas is mainly used to fill hot air and party balloons. Balloons filled with it float upwards and this phenomenon is achieved as helium gas is less dense than air.
See also
*
Noble metal
A noble metal is ordinarily regarded as a metallic chemical element that is generally resistant to corrosion and is usually found in nature in its raw form. Gold, platinum, and the other platinum group metals ( ruthenium, rhodium, palladium, o ...
References
{{Reflist
Chemical nomenclature
Chemical properties
Gases
Industrial gases
Noble gases