The Noble Gases (Group 18) |
The Noble Gases |
The noble gases were previously referred to as inert gases, but this term is not strictly accurate because several of them
do take part in chemical reactions.
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There are seven Noble gases; helium, neon, argon, krypton, xenon, the radioactive radon and the newly synthesized ununoctium.
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Properties |
Under standard conditions, the noble gasses all occur as monatomic gases. |
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Reactions |
Noble gases have full valence electron shells, valence electrons are the outermost electrons of an atom and are normally the only electrons which can participate in chemical bonding. According to atomic theory derived from quantum
mechanics and experimental trends, atoms with full valence electron shells are extraordinarily stable and therefore do not form chemical bonds.
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All of them exihibit an extremely low chemical reactivity, in fact no conventional compounds of helium or neon have yet been prepared. Xenon and krypton are known to show some reactivity in the laboratory. Recently argon compounds have also been successfully characterised.
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Because of their unreactivity, the noble gases were not discovered until 1868, when helium was detected spectrographically in the Sun. The isolation of helium on Earth had to wait until 1895. The noble gases have very weak inter-atomic forces of attraction, and consequently very
low melting points and boiling points. This is why they are all gases under normal conditions, even those with larger atomic masses than many normally solid elements.
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Uses |
The most commonly encountered uses of the noble gases in everyday life is in lighting. Argon is often used as a suitable safe and inert atmosphere for the inside of filament light bulbs, and is also used as an inert
atmosphere in the synthesis of air and moisture sensitive compounds (as an alternative for nitrogen). Some of the noble gases glow distinctive colours when used inside lighting tubes (neon lights). Helium, due to its unreactivity (compared to flammable hydrogen) and lightness, is often used in blimps and balloons.
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