Noble Gases
The noble gases are located in Group 18 (VIIIa) of the periodic table. The noble gases are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), and ununoctium (Uuo). The noble gases are also known as the inert gases. Noble gas is translated from the German noun Edelgas, first used in 1898 by Hugo Erdmann to indicate their extremely low level of reactivity. The name makes an analogy to the term "noble metals", which also have low reactivity. The Noble gases were not discovered until 1892 because the noble gases are highly un-reactive, they remained hidden in the atmosphere. They make up only 1% percent of the atmosphere.
Properties of noble gases:
Noble gases are colourless, odourless, tasteless, nonflammable gases.
All the Noble gases have eight electrons in their outermost electron shell. That means they have complete valence shell
Noble gases have similar chemical and physical properties because they all have eight electrons in their outer shell.
Because of their full outer shells, the Noble gases do not form compounds with other metal or non metal elements.
They are all colorless monatomic gases which do not form ionic or covalent compounds with any other elements.
They also have extremely low melting and boiling points which increase slightly as you descend the group. Their low melting and boiling points makes them useful as cryogenic refrigerants.
Noble gases are fairly nonreactive
Noble gases have high ionization energies
Noble gases havevery low electronegativities
The six noble gases that occur naturally are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn). Ununoctium (Uuo) is currently the only synthetic noble gas.
Physical and atomic properties of noble gases:
| Property | Helium | Neon | Argon | Krypton | Xenon | Radon | Ununoctium |
|---|---|---|---|---|---|---|---|
| Density (g/dm³) | 0.1786 | 0.9002 | 1.7818 | 3.708 | 5.851 | 9.97 | (predicted) 13.65 g·cm-3 |
| Boiling point (K) | 4.4 | 27.3 | 87.4 | 121.5 | 166.6 | 211.5 | (extrapolated) 350±30 |
| Melting point (K) | 0.95[25] | 24.7 | 83.6 | 115.8 | 161.7 | 202.2 | |
| Enthalpy of vaporization (kJ/mol) | 0.08 | 1.74 | 6.52 | 9.05 | 12.65 | 18.1 | |
| Solubility in water at 20 °C (cm3/kg) | 8.61 | 10.5 | 33.6 | 59.4 | 108.1 | 230 | |
| Atomic number | 2 | 10 | 18 | 36 | 54 | 86 | 118 |
| Atomic radius (calculated) (pm) | 31 | 38 | 71 | 88 | 108 | 120 | (predicted) 152 |
| Ionization energy (kJ/mol) | 2372 | 2080 | 1520 | 1351 | 1170 | 1037 | 1st: (extrapolated) 839.4 |
| Allen electronegativity | 4.16 | 4.79 | 3.24 | 2.97 | 2.58 | 2.60 |
Chemical properties of noble gases:
| Element | Symbol | Atomic number | No. of electrons/shell |
|---|---|---|---|
| helium | He | 2 | 2 |
| neon | Ne | 10 | 2, 8 |
| argon | Ar | 18 | 2, 8, 8 |
| krypton | Kr | 36 | 2, 8, 18, 8 |
| xenon | Xe | 54 | 2, 8, 18, 18, 8 |
| radon | Rn | 86 | 2, 8, 18, 32, 18, 8 |
| ununoctium | Uuo | 118 | 2, 8, 18, 32, 32, 18, 8 (predicted) |