NEET Chemistry Notes p-Block Elements – Group-16 Elements Oxygen Family
Group-16 Elements Oxygen Family
Group-16 Elements Oxygen Family
16th group elements are sulphur (S), selenium (Se), tellurium (Te) and polonium (Po). This is sometimes known as group of chalcogens (due to ore forming nature). Oxygen is the most abundant of all the elements on earth. Oxygen and sulphur are non-metals, selenium and tellurium are metalloids and polonium is radioactive metal.
Important Properties
The group 16 elements exhibit the properties may be given as:
Physical Properties
- Group-16 elements show following trends in their physical properties
- Ionisation energies On moving down the group from oxygen to polonium, the ionisation energy decreases because of increase in atomic size.
- Metallic character On moving down the group, the metallic character increases down the group from oxygen to polonium because of decrease in ionisation energy.
- Oxidation states Group VIA elements show oxidation state of + 2, + 4 and + 6 due to the promotion of electrons to vacant d-orbitals. But down the group +4 oxidation state becomes more stable.
- Allotropy Oxygen exists in two allotropic forms as02 and 03 (ozone). Sulphur exists in a number of allotropic forms such as rhombic, monoclinic and plastic sulphur. Selenium has two common forms red (non-metallic) and white grey (metallic). Tellurium occurs in two allotropic forms, crystalline and amorphous. Polonium also exists in a- and p- forms (both metallic).
Chemical Properties
Following are the main chemical properties of group-16 elements
Hydrides All the elements of the oxygen family form stable hydrides of the type H2M either by directly combining with hydrogen or by the action of acids on metal sulphides, selenides and tellurides.
The decreasing bond dissociation enthalpy of the M—H bond is due to increase in the size of M which explains the increasing acidic character of hydrides down the group.
Halides All the elements of the oxygen family form a number of halides.
Oxides These form oxides of the type M02 and M03.
Some Important Compounds of Oxygen
Dioxygen
Preparation
- Laboratory method
- It is manufactured from liquid air. Air is liquefied by making use of Joule Thomson effect. Liquid air is a mixture of liquid nitrogen and liquid oxygen.
The difference in their boiling points is about 12.8°C, hence, they are easily separated by fractional evaporation. - By electrolysis of water (acidified water)
Properties
- Colourless, odourless, tasteless gas which is slightly soluble in water. Liquid oxygen exhibits paramagnetism.
- It is non-inflammable but a supporter of combustion.
, bond dissociation energy is high, therefore it reacts with metals or non-metals after external heating to start the reaction.
Uses
- In oxyacetylene and oxyhydrogen flames.
- Liquid 02 is used as a rocket fuel.
- For life support systems, e.g. in hospitals and in water diving for divers, for miners and mountaineers.
- As an oxidising and bleaching agent.
Ozone(03)
It is formed in the upper layer of atmosphere by the action of UV rays from sun on oxygen. It prevents the UV rays from entering the earth’s atmosphere. CFCs, common refrigerants deplete the ozone layer.
Preparation
It is prepared in ozoniser by subjecting dry and cold dioxygen to the action of silent electric discharge.
Properties
- It is pale blue gas with pungent odour. It is diamagnetic and poisonous.
- Ozone is unstable
Uses
- As a germicide and disinfectant for sterilizing water.
- As a bleaching agent for oils, ivory wax and delicate fibre.
- For detecting the position of double bond in unsaturated compounds. In destroying odours coming from cold storage room, slaughter houses and kitchen of hotels.