1 Group 15 - Pnicogens –N is diatomic; P, As & Sb have multiple allotropes N & P are nonmetals As & Sb are metalloids Bi is a metal. –They form monoatomic -3 anions. –Metal can exist as cations such as: Sb 3+ and Bi 3+ also exist –Five valence electrons: [N.G.] ns 2 np 3 –Negative ΔH electronic attraction Melting Point Boiling Point State (at 20 °C) Density (at 20 °C) Nitrogen-210 °C-196 °CGas g/cm 3 Phosphorus (white) 44 °C280.5 °CSolid2.2 g/cm 3 Arsenic (grey)817 °C * 616 °C * Solid5.78 g/cm 3 Antimony (grey)631 °C1635 °CSolid6.69 g/cm 3 Bismuth271 °C1580 °CSolid9.75 g/cm 3 Images from

Nitrogen Reactivity Nitrogen is a very stable, unreactive, diatomic molecule (N 2 ), as it has a strong triple bond. N 2 is used as an inert atmosphere for chemical reactions and for production of electronic components. Much cheaper than the most common alternative, argon. (Air is 78% N 2, 21% O 2 and 1% Ar) Nitrogen reacts spontaneously with Li and with the alkaline earth metals: The reaction between nitrogen and hydrogen is exothermic, however it does Not take place without a catalyst.

Nitrogen N is an essential element for life, ironically most organism cannot utilize elemental nitrogen (N 2 ), instead requiring nitrogen to be “fixed” either as as a nitrate, an ammonium salt or some other nitrogen containing metabolite. Haber-Bosch process: -The major industrial method for making ammonia - N 2 and H 2 are combined in the presence of catalyst at a high T (400 o C) and P (~200 bar): - The reaction is forced forward removing NH 3 as it is produced by cooling it to a liquid. Why? - NH 3 condenses at a much higher temperature than N 2 or H 2. Why? - The unreacted N 2 and H 2 are recycled allowing for almost 100% yield over time.

Haber-Bosch process

Ammonia - A weak base when dissolved in water: i.e only some of the ammonia reacts with the water: NH 3(aq) is often referred to as NH 4 OH (aq),as the equilibrium is reactant favoured, NH 3(aq) is a better description. - Ammonia reacts completely with the strong acids. It should be kept well away from nitric acid as the product of that reaction is highly explosive! What is this product? Write a balanced equation for the reaction between ammonia and nitric acid. Many other explosive compounds contain nitrogen because N 2(g) is such a stable molecule that reactions producing it tend to be very exothermic. e.g. azides (N 3 - salts), nitrates (TNT & nitrocellulose)

Phosphorus There are two major allotropes of phosphorus: i) White phosphorus (P 4 ) is soft and waxy and so reactive with air that it is stored under water. It can ignite spontaneously in air ii) Red phosphorus (P, a network solid) is formed when white phosphorus is heated to o C away from air. iii) Black phosphorus and violet phosphorus also exist. They are both network solids.

Phosphorus As we saw in the halogens section, phosphorus reacts with the halogens to make PX 3 which, on reaction with more halogen, makes PX 5. It isn’t surprising that P 4 is so reactive given its structure. Compare the bond angles in P 4 to the bond angles the atoms “should” have.

Phosphorus Phosphorus forms strong bonds with oxygen, and there are several phosphorus oxides, phosphates, phosphites and phosphoric acids. We saw that the sulfur oxides were acidic. This can be generalized to all nonmetal oxides. The two main oxides of phosphorus are P 4 O 6 and P 4 O 10. What is formed when each reacts with water? Do you remember what was unusual about phosphorous acid?

Phosphorus Phosphoric acid can polymerize. i)H 3 PO 4 is “orthophosphoric acid” ii)ii) Two H 3 PO 4 combine as “diphosphoric acid” (or “pyrophosphoric acid” or phosphoester) releasing a molecule of water: ii) When a third molecule of H 3 PO 4 is added to the chain, “triphosphoric acid” (or phosphodiester) is produced: The phosphodiester bond contains a lot of easily accessed energy for biological reactions. Molecules such as ATP and DNA phosphoester bonds.