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•Discuss the similarities and differences in the chemical properties of elements in the same group
Chem. Properties of groups Chem. Properties of groups3.3.1
Where are the noble gases?
The elements in group 0, on the right of the periodic table, are called the noble gases.
He
Rn
Xe
Kr
Ar
Ne
helium
neon
argon
krypton
xenon
radon
Discovery of argon
Because the noble gases are so unreactive, they were very difficult to identify.
The first noble gas, helium, was discovered on the Sun in 1868 by William Ramsay and Morris Travers. It was not known to exist on Earth until 1895.
In the early 1890s, a British physicist Lord Rayleigh found that nitrogen obtained from the air was very slightly denser than nitrogen obtained from decomposing ammonia.
He and his colleague William Ramsay investigated this and found that the nitrogen from the air contained a small quantity of an inert element.
They finally managed to isolate the element, which they called argon.
Discovery of argon
Ramsay realised that there was no place for this new gas in the periodic table, and he predicted that it belonged to a whole new group of elements.
Radon was discovered in 1900.
He experimented on the argon with his colleague Morris Travers, and in 1898, they discovered that the argon actually contained tiny quantities of the three other noble gases, neon, krypton and xenon.
Why are they called the ‘noble gases’?
They are all very unreactive.
The noble gases all form colourless gases at room temperature.
The name was changed to ‘noble gases’ as they were considered similar to the very unreactive precious metals gold and platinum, which are sometimes called ‘noble’ metals.
Now only neon and helium have not yet been made to form compounds.
Noble gases were originally called ‘inert gases’, as they were thought not to react with anything. Then in 1962, a British chemist, Neil Bartlett, made a compound with xenon.
The noble gases
Why are the noble gases so unreactive?
helium2
neon2,8
argon2,8,8
How does electron structure affect reactivity?
They do not normally form bonds with other elements.
All noble gases have full outer electron shells and do not need to gain, lose or share electrons.
The noble gases are very stable and the most unreactive (or inert) of all the elements. All of the noble gases are similarly unreactive, up and down the group.
They are monatomic, which means they exist as individual atoms. Most other gases are diatomic.
This means that:
8
Why is it called group 0?
Why is group 0 not called group 8, even though it comes after group 7?
In the rest of the periodic table, the number of the group is the same as the number of outer shell electrons in the elements of that group.
However, this is not true for the noble gases. Helium only has 2 electrons in its outer shell, while the others all have 8.
Rn
Xe
Kr
Ar
Ne
He
0
It used to be called group 8, and still is in some cases.
Because of this, the group’s number was changed to 0.
