Group VIIIA: Noble Gases

Submitted by ChemPRIME Staff on Thu, 12/16/2010 - 14:36


The properties of the noble gases are summarized in the table below. The noble gases have a complete octetA stable set of eight electrons in the valence shell of an atom. Each noble-gas atom has an octet. of electrons ns2np6 or just ns2 for helium, leaving them with little chemical reactivity. Sure enough,the ionizationA process in which an atom, molecule, or negative ion loses an electron; a process in which a covalent molecule reacts with a solvent to form positive and negative ions; for example, a weak acid reacting with water to form its conjugate base (an anion) and a hydrogen (hydronium) ion. energies of He and Ne are greater than 2000 kJ mol–1, and it is unlikely that these noble gases will ever be induced to form chemical bonds. The same probably applies to Ar. Kr and especially Xe do form compounds though, which was discussed in the halogens section, and Rn might be expected to be even more reactive. Rn is radioactiveDescribes a substance that gives off radiation‐alpha particles, beta particles, or gamma rays‐by the disintegration of its nucleus., however, and study of its chemistry is difficult.

Properties of the Group VIII Elements.

Element Symbol Electron

Configuration

Usual

Oxidation State

Radius/pm - Covalent


Helium He 1s2 0 ...


Neon Ne [He]2s22p6 0 ...


Argon Ar [Ne]3s23p6 0 ...


Krypton Kr [Ar]4s23d104p6 +2 110


Xenon Xe [Kr]5s24d105p6 +8, +6, +4, +2 130



Symbol Ionization Energy/MJ mol–1 Density/

g cm–3

Electro-

negativity

Melting

Point (in °C)

First Second
He 2.379 5.257 0.179 ... -272


Ne 2.087 3.959 0.901 ... -249
Ar 1.527 2.672 1.78 ... -190
Kr 1.357 2.374 3.74 2.6 -157
Xe 1.177 2.053 5.86 2.4 -112


Because of the lack of reactivity of the noble gases, they are often used when an nonreactive atmosphereA unit of pressure equal to 101.325 kPa or 760 mmHg; abbreviated atm. Also, the mixture of gases surrounding the earth. is needed, such as in welding. Due to their low boiling points, noble gases are also cryogens in their liquidA state of matter in which the atomic-scale particles remain close together but are able to change their positions so that the matter takes the shape of its container forms. One familiar use of helium is in balloons and blimps, since it is buoyant in the atmosphere, and unlike hydrogen, nonreactive. Another familiar use is as lighting in gas discharge lamps. Referred to popularly as neon lights, they can contain other noble gases, or mixtures of the gases.