Oxygen is the most abundant of all the elements. It occurs in the free state asO2 and makes 20.46% by volume. It also occurs in the form of ozone.It makes up 46.6% by weight of the earth's crust.Sulphur occurs less abundantly. Selenium and tellurium are less abundant than sulphur and occur as selenides and tellurides in sulphide ores.
General characteristics of oxygen family
Physical state and molecular structure of oxygen family
The elements of oxygen family have six electrons in the valence shell. The electronic configuration is ns2np4.
Atomic and ionic radii
The atomic radii of group 16 are smaller than those of group 15 elements. The atomic radii of the elements of oxygen family increase down the group.
Ionization enthalpy of oxygen family
The first I.E of group 16 are unexpectedly lower while their second I.E are higher than those of the corresponding elements of group 15.
Electron gain enthalpy
The elements of group 16 have two electrons less than nearest noble gas configuration. They have high tendency to accept electrons and have large negative electron gain enthalpies. The value for oxygen is least negative in this group.
Electronegativity of oxygen family
The elements of group 16 have higher E.N values than the group 15 elements. Oxygen is the second most electronegative element. Electronegativity decreases down the group.
Metallic and non-metallic character
Because of high I.E, the elements of group 16 are less metallic. As we move down the group, the I.E decreases and hence the metallic character increases.
Melting point of oxygen family
The melting point increase regularly as we go down the group up to tellurium. The melting points of polonium are lower than those of tellurium.
Boiling point of oxygen family
The boiling point increase regularly as we go down the group up to tellurium. The boiling points of polonium are lower than those of tellurium.
Atomicity of oxygen family
Oxygen exists as diatomic gas at room temperature because of the absence of d-orbitals in oxygen molecule, while other exist as octa-atomic solids, .
Catennation property of oxygen family
Because of stronger S-S bonds as compared to O-O bonds sulphur has more tendency to form catenation than oxygen.
Trend in density of oxygen family
Metallic character increases down the group, with tellurium classified as a metalloid and polonium as a metal. Melting point, boiling point, density, atomic radius, and ionic radius all increase down the group.
Occurrence of oxygen
Oxygen is the most abundant element on earth, constituting about half of the total material of its surface. Most of this oxygen is combined in the form of silicates, oxides and water. It makes up about 90% of water, two thirds of the human body and one fifth by volume of air.