The appearance of Group 5 elements varies widely. Nitrogen is a colourless, odourless gas; Phosphorus exists in white, red and black solid forms; Arsenic is found in yellow and grey solid forms; Antimony is found in a metallic or amorphous grey form; and Bismuth is a white, crystalline, brittle metal. These appearences reflect the changing nature of the elements as the Group is descended, from non-metal to metal.
The elements of the Group show a marked trend towards metallic character on descending the Group. This trend is reflected both in their structures and in their chemical properties, as for example in the oxides which become increasingly basic.
Occurrence and Extraction
Nitrogen is found free in the atmosphere, and accounts for 78% of the air by volume. Phosphorus is not found free in nature, but occurs isn several minerals and ores such as Phosphate Rock. The other elements are found in the elemental form in the Earth's crust, but more frequenelty as minerals.
The physical properties of this Group vary widely as Nitrogen is a gas, and the other elemnets are solids of increasingly metallic nature.
Nitrogen exists as the diatomic molecule N2. It is a colourless, odourless gas, which condenses to a colourless liquid at 77K.
Phosphorus has at least two allotropes, red and white Phosphorus. White Phosphorus is a solid composed of covalent tetrahedral P4 molecules, and red Phosphorus is an amorphous solid which has an extended covalent structure.
The covalent radii of the atoms increases on descending the Group. However, the Nitrogen atom is anomalously small and so it can multiple-bond to other Nitrogen, Carbon and Oxygen atoms.
Nitrogen is very unreactive. The only element to react with Nitrogen at room temperature is Lithium to form the nitride Li3N. Magnesium will also react directly with Nitrogen, but only when ignited. Some micro-organisms have developed a method for reacting directly with Nitrogen gas and building it into proteins. This is called 'Nitrogen Fixing' and is an important part of the food chain.
Phosphorus is more reactive than Nitrogen. It reacts with metals to form phosphides, with Sulphur to form sulphides, with Halogens to form halides, and ignites in air to form oxides. It also reacts with both alkalis and concentrated Nitric acid.
There are five oxides of Nitrogen;