General Introduction
Fig 1: The nitrogen family
Group 15 elements are also called the nitrogen family. This family contains metals, nonmetals as well as metalloids. There are two nonmetals, nitrogen and phosphorus. These nonmetals usually gain or share three electrons when they react with other elements. Nitrogen and phosphorous interestingly a part of several important biological materials that store genetic information and energy in living organisms. Nitrogen is found abundantly in the air and it takes up 80% of the atmosphere. Nitrogen is highly unreactive which means that it does not readily react with other elements, so you breathe out as much nitrogen as you breathe in. Alternatively, Phosphorus is much more reactive, so phosphorus in nature is always found in in the form of its compounds.
Nitrogen is a diatomic gas (N2) which has a very low boiling point. The low boiling point is because of its very weak intermolecular forces. Phosphorus exists most commonly as tetrahedral P4 molecules. It has stronger dispersion forces than N2. It is highly reactive and it bursts into flame in the presence of air and this is the reason why it is stored under water. Many fertilizers contain nitrogen and phosphorus. Arsenic naturally exists as a crystal in the form of extended sheets of As atoms covalently bonded together. The covalent network structure gives it a high melting point. It is a metalloid and is used as a semiconductor. It is highly poisonous and used as a weed killer and rat poison. Antimony also has a covalent network structure. It is a brittle metalloid used on electronics. Bismuth has metallic bonding and a melting point lower than As and Sb. Likewise, all but Bi are important donor atoms in their trivalent compound state. For instance, even though bismuth shows metallic properties, sodium bismuthate is a very strong oxidizing agent. This is possible due to inter pair effect. It also happens to be the heaviest naturally occurring metal that is not radioactive. It is used in paint pigments, electrical solder and heads of fire sprinkler systems,
Nitrogen is obtained from the fractional distillation of liquefied air. Phosphorus is derived from phosphate minerals.
Ca3(PO4)2(s) + 3SiO2(s) + 5C(s) 2P(l) + 3CaSiO3(s) + 5CO(g)
Arsenic is prepared by heating a mixture of FeAs2 and FeS2 in the absence of air.
Antimony is prepared by roasting the ore stibnite, Sb2S3.
Note that, the higher elements in the group are metallic and lose electrons to form cations. This happens because with increasing electron configuration, the ability to form p-p pi bonding reduces and d orbitals may be utilized to form d-p pi bonds. Oxides of group 15 elements change from acidic to amphoteric to basic as we move down the group. All Group 5A(15) elements form gaseous hydrides with the formula EH3. All except NH3 are extremely reactive and toxic. Except for nitrogen, all other elements are solids that show allotropy.
Group 5 elements can form 3 covalent bonds by sharing 3 unpaired electrons. The produce compounds with a variable oxidation state such as +3 or –3. Each atom has a lone pair of electrons which enables atoms to form dative covalent bonds. Hence, Group 5 elements can form some compounds with an oxidation state of +5 as well. Likewise, these elements form binary compounds upon direct interaction with many other elements.