Introduction
Elements of group 13 to 18 of the periodic table are collectively called 'p' block elements. The general electronic configuration of these elements is ns2np1-6. They involve the filling up of 'p' orbitals of their outermost shells, when their 's' orbitals are already filled. Some of the 'p' block elements such as boron, carbon, nitrogen, and oxygen, form very important compounds. The occurrence, preparation and properties of these elements and the chemistry of their compounds are focused here.
Boron
Boron (B) is the first member of group 13 of the periodic table and is the only non-metal of this group. It has an electronic configuration of 1s2 2s2 2p1 with only three electrons in its valence shell.
Compounds of Boron
The hydrides of boron are known by a general name borane. These boranes are gaseous substances at room temperature. The general formulae of the two important series of boranes are BnHn+4 and BnHn+6. Amongst the well known boron hydrides are: diborane (B2H6), tetraborane (B4H10), pentaborane (B5H9), and hexaborane (B6H10), etc. The simplest and the most important hydride of boron is diborane.
Compounds of Boron - Borax and Boric acid
Borax (Na2B4O7.10H2O)
Borax occurs naturally as tincal (contains about 55% borax) in certain inland lakes of India, Tibet and California (U.S.A.).
Carbon
Carbon forms the largest number of compounds, next only to hydrogen. It ranks seventeenth in the order of abundance in the earth's crust. Carbon occurs in the free native state as well as in the combined state. Carbon and its compounds are widely distributed in nature.
Compounds of Carbon
Inorganic compounds
Carbon compounds with those elements having their origin in minerals, such as oxygen, halogens and metals are called inorganic compounds. Inorganic compounds of carbon do not have carbon-carbon bonds. For example, CO, CO2, SiC etc., are inorganic carbon compounds.
Oxides of Carbon
Carbon combines with oxygen at higher temperature to form oxides, viz., carbon monoxide (CO) and carbon dioxide (CO2).
Carbonates and Bicarbonates
Carbonic acid is a dibasic acid that gives rise to two series of salts, carbonates (normal salts) and bicarbonates (acid salts), due to successive removal of the replaceable hydrogens from H2CO3.
Bicarbonates of calcium and magnesium are responsible for temporary hardness of water.
Halides of Carbon
Carbon combines with all the halogens to form tetrahalides, viz., CF4, CCl4, CBr4 and CI4, mixed tetrahalides like CFCI3, CF2Cl2 and CCl3Br, and trihalides of the formula CHX3, viz., chloroform, CHCl3 and iodoform, CHI3.
Carbides
The compounds of carbon with elements more electropositive than itself are called carbides. Thus, carbon combines with metals such as Be, B, Si etc.to give carbides.
Sulphides of Carbon
Pure CS2 is colorless, flammable and volatile liquid. However, impure carbon disulphide has yellowish color and bad odor due to the impurities of sulphur and hydrogen sulphide.
Nitrogen
In 1772 Daniel Rutherford discovered Nitrogen. Nitrogen is the first member of group 15 of the periodic table. Nitrogen exists as a diatomic molecule (N2) with a triple bond between the nitrogen atoms (NN). So nitrogen gas is also called dinitrogen. Its electronic configuration is 1s2 2s2 2p3.
Oxides of Nitrogen
Oxides of nitrogen provide a fascinating picture from the point of view of their varied structures and diverse chemical behavior. They range from N2O (oxidation state of nitrogen +1) through NO, N2O3, NO2, N2O4 to N2O5 in which the oxidation state of nitrogen is from +2 to +5.
Ammonia
Ammonia (NH3) is an important compound of nitrogen and hydrogen. It is produced by the natural decomposition of animal and vegetable bodies. The death and decay of plants and animals cause the nitrogen compounds present in them to get decomposed, giving ammonia. Ammonia also occurs in the soil in the form of ammonium salts.
Nitric Acid
The most important and useful oxoacid of nitrogen is nitric acid. Its molecular formula is HNO3 and molar mass 53 g mol-1.
Chemical Properties of Nitric Acid
Thermal stability
On heating, HNO3 decomposes to give NO2.
Nitric Acid - Uses and Tests
* The manufacture of important fertilizers such as ammonium nitrate and basic calcium nitrate.
* The manufacture of explosives like T.N.T, nitroglycerine, etc.
* Manufacture of artificial silk, dyes and plastics, and nitro derivatives of organic compounds.
Oxygen
Oxygen is very essential for the existence of human life on Earth. It is the most abundant element on the surface of the Earth. In a free state, it is present in the Earth's atmosphere to an extent of about 21% by volume, (23.15% by mass) In the combined form, it constitutes about 88% by mass of water and 45.5% by mass of the earth's crusts. SiO2 (silica, quartz), CaCO3 (limestone) and Fe2O3 (iron ore called haematite) are some typical examples of oxygen containing minerals.
Properties of Oxygen
Metals such as silver, gold and platinum adsorb oxygen gas at 500oC. Molten silver absorbs ten times its mass of oxygen and expels it rapidly on cooling. This phenomenon is called the spitting of silver.
Oxides
Oxides are binary compounds of oxygen with another element, e.g., CO2, SO2, CaO, CO, ZnO, BaO2, H2O, etc. These are termed as oxides because here, oxygen is in combination with only one element.
Ozone
Ozone is an allotropic form of oxygen. Its molecular formula is O3 and molar mass is 48 g mol-1. Schonbein (1840) concluded that Van Marums observations in 1785 of a peculiar smell, when an electric discharge was passed through oxygen (or air), was in fact a new gas. He named it Ozone, which is derived from a Greek word ozoaterr meaning smell. Soret in 1860, assigned the molecular formula O3.
