Do you know it's helium gas that is filled in the balloons we used to play with? Helium is a noble gas but its properties are quite different from the properties of other noble gases. Group 18 elements consist of the noble gases which were not known at the time of Mendeleev and so were not added to the Mendeleev's periodic table but later after the discovery of helium and argon in the periodic table Ramsay in 1896 suggested a new group for such noble gases.
The new group formed was known as zero group having 6 elements in it. These elements came to be known as noble gases, inert gases, the zero group elements or the group 18 elements.
We can define noble gases as those monoatomic gases whose chemical reactivity is very low. So let's get started with the characteristics of group 18 elements.
Group 18 elements are known as noble or inert gases. They are called inert because they do not take part in any chemical reaction and so we can say that they are chemically inert.
All the elements of group 18 i.e. Helium (He), Neon(Ne), Argon(Ar), Krypton(Kr), Xenon(Xe), Radon(Rn), Organesson(Og) are non-metallic elements.
The zero group occupies the intermediate position between the strong electronegative elements of VIIA and strong electropositive elements of IA groups in the periodic table and this they act as a bridge.
In the long form of the periodic table, the noble gases are in group 18 which is placed in the extreme right of the table.
All the members of the 18th group posses 8 electrons in their outermost shell.
All the gases except for helium possess ns2, np6 configuration. Except for helium, the differentiating electron enters into p-subshell and thus, these all are included in p-block elements.
All the noble gases except helium which has 1s2 configuration, a completely filled 1st shell have their outermost shell with a complete octet.
Their outer shell configuration is:
Rest all: ns2 np6
These elements also called noble gases to have no tendency to lose or gain electrons because of completely filled outer shell or stable configuration and so usually under normal conditions do not participate in chemical reactions.
Under ordinary conditions of temperature and pressure, all of these group 18 elements are gases. Out of all these noble gases, Rn and Og are radioactive rest all are present in the atmosphere in very minute quantities.
These were named rare gases because their presence in the atmosphere is very minute.
These were named as inert gases because they do not participate in any chemical reactions.
These were named as noble gases however, a number of xenon compounds and two Krypton fluorides were prepared.
All of them are monoatomic gases.
These were some of the characteristics of inert gases. Let's now look at some physical characteristics of noble gases.
These gases are colourless, tasteless and odourless.
The Van der Waals forces between the particles of these elements is weak and it becomes stronger as we move down the group. This is because there is an expansion in the polarising capacity of the molecules.
They have a stable nature and so in free state, these are monoatomic gases.
The boiling and melting points of noble gases is low. The weak Van der Waals forced is the reason behind low melting and boiling point of these gases However these increase as we move down the group.
These elements can be condensed at very low temperatures. Ease of liquefaction increases down the group as the size of the atom increases.
These are slightly soluble in water. From He to Rn solubility increases.
In their respective periods, the atomic radii of the noble gases are the largest.
Because the electronic configuration is stable the ionization enthalpies of these noble gases are the highest in their respective periods.
The order of electron gain enthalpy of these group 18 elements is such :
This was all about, noble gases share which characteristics now let's have a look at some other aspects of the noble gases.
Out of all the noble gases, helium is of great importance in the industrial markets, chemical use and also in our day to day lives. Let's look at some important uses of helium.
Oxygen cylinders used underwater for proper breathing has helium as its major component.
Helium can be used as a cooling gas in gas-cooled atomic reactors.
Helium can be used as a streaming gas in gas-fluid chromatography.
In Cryoscopy helium is used for the superconductivity.
Air balloons are filled with helium. It is also used in the aircraft because it has a very low density and is flammable.
To perform tests at very low-temperature fluid helium is used as the cryogenic agent because of its very low boiling point.
1. Group 18 Elements are Reactive? Why?
The group 18 elements are called noble or inert gases. As the name suggests these are inert because chemically they are very less reactive or not at all reactive.
This is so because they have stable electronic configuration which means they have no tendency to lose or gain electrons because of completely filled outer shell. The full valence electron shells of these atoms make the noble gases extremely stable. These are extremely non-reactive. Usually, under normal circumstances, they do not react or take part in any chemical reactions however there exist some exceptions.
2. Give Some Uses of Noble Gases
The below mentioned are some prominent uses of the group 18 elements or the noble gases.
Neon is used in fluorescent bulbs, it is also used in various release tubes. The reddish-orangish shine to these bulbs is given by the neon itself.
Argon is used in various metallurgical processes. Also gives a stable atmosphere in research centres.
Radon can be used in the treatment of cancer.
Krypton is used in fibre lights also in release tubes.