Group 16-Atomic properties
Group 16 elements are oxygen, sulphur, selenium, tellurium and polonium.
They are together called Chalcogens.
Let us look at the occurrence of each of the Group 16 elements.
Oxygen, a group 16 element, is the most abundant element on earth's crust.
Oxygen forms about 46.6% by mass of earth’s crust.
Dry air contains about 21% of oxygen by volume.
Next, sulphur forms only 0.03-0.1% of the earth’s crust.
Sulphur exists in the combined state primarily as sulphates mentioned here.
Sulphur can also exists as sulphides as mentioned here
Traces of sulphur also occur as hydrogen sulphide in volcanoes.
Organic materials egg, protein, garlic, onion, mustard, hair and wool contain sulphur.
The Pungent smell of rotten eggs is because of sulphide.
Other group 16 elements, Selenium and tellurium are found as metal selenides and tellurides in sulphide ores.
Finally, polonium occurs in nature as a decay product of thorium and uranium minerals.
Up next, let us look at the electronic configuration of Group 16 elements.
All the Group 16 elements have 4 electrons in the outer p-orbital.
It is evident from the electronic configuration that new shells are added as we go down the group.
With addition of new shells, the atomic and ionic radii increase down the group.
Also, with the increase in atomic size, the outermost electron is further away from the nucleus.
Making it easy to lose the outermost electron from the atom. As a result, ionisation energy decreases down the group.
Also, if we compare the ionisation enthalpy of group 16 elements with that of group 15, we find that group 16 elements have lower ionisation enthalpy.
This is because group 15 elements have extra stable half filled p-orbitals, and therefore is difficult to remove an electron from it.
Next atomic property, electron affinity decreases as we go down the group.
However, we have an exception. O has less electron affinity than S.
This is because the size of oxygen is very small, where the valence electrons are placed very closely.
Addition of an external electron, will result in increase electron-electron repulsion.
Hence, electron affinity of group 16 follows the order: S>Se>Te>Po>O
Finally, electronegativity values also decrease as we go down group 16.
This is again because tendency to hold shared pairs of electrons towards itself decreases as the size increases.
In fact, O is the second most electronegative element after fluorine in the periodic table.
The decrease in electronegativity also implies that metallic character increases down the group from O too Po.
Group 16 elements are collectively called Chalcogens.
Oxygen is the most abundant of all the elements on earth while the other group 16 elements are found only in small traces.
Trend of physical properties of group 16 elements.