Group 16 of periodic table includes oxygen (O), Sulphur (S), Selenium (Se), Tellurium (Te) and Polonium (Po). These are collectively known as Chalcogens or ore forming elements. The first four members are non – metals. Polonium is having metallic character and is radioactive.
General introduction to Oxygen family
Its name came from oxys + genes, “acid former” was discovered in 1772 by Schelle and independently by Pristeley in 1774.
Oxygen is the most common element in the earth’s crust and makes up about 20% of the air we breathe. Oxygen is gas at room temperature and is colourless, odourless and testless. Liquid oxygen has a slight blue colour. Oxygen exists in two allotropes, oxygen in air (O2) and ozone in air (O3) ozone is very reactive and used bleaching and disinfectant reagent.
Sulfur was classified as an element in 1777 by Lavoisier. Pure sulfur is testless and odourless with white yellow colour. Sulfur is the tenth most abundant element in the known universe. Sulfur exists in three allotropic forms. Two are crystalline and one is amorphous. The most significant compound of sulfur used in modern industrialized societies is sulphuric acid (H2SO4). Sulphur dioxide (SO2) is used in bleaching and refrigeration. SO2 gas reacts with water vapour in air to produce a weak acid, sulfurous acid (H2SO3) which contributes to the acid rain problem.
It was discovered by Berzelius in 1818. Its name came from the Greek work Selene which is used for moon. It is an important semiconductor which is particularly sensitive to light. There are at lest two other allotropes of the element, including a semi – metallic state.
Discovered by Von Reicherstein in 1782. It is brittle metalloid that is relatively rare. It is named from the Latin tellus for ‘earth’. Tellurium can be alloyed with same metals to increase their machinability and is a basic ingredient in the manufacture of blasting caps.
It was discovered in 1898 by Marie Curie and named for her native country Poland. Although radioactive, polonium has a few commercial uses. It is synthesized in the lab rather its recovery from minerals.
GENERAL TRENDS IN PHYSICAL PROPERTIES
|Common oxidation state||-2||-2, +4, +6||+4, +6||+4, +6|
|Atomic radius (pm)||66||104||116||143||167|
|First ionization energy (KJ/mol)||1314||1000||941||869||812|
Illustration 1. Name two compounds in which oxygen has oxidation state different from – 2.
Give oxidation states also.
Solution: (i) OF2 (Oxidation state of O = +2)
(ii) H2O2 (Oxidation state of O = – 1)
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