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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: Sb3+ and Bi3+ also exist– Five valence electrons: [N.G.] ns2 np3

– Negative ΔHelectronic attraction

Melting Point

Boiling Point

State (at 20 °C)

Density (at 20 °C)

Nitrogen -210 °C -196 °C Gas 0.00125 g/cm3

Phosphorus (white)

44 °C 280.5 °C Solid 2.2 g/cm3

Arsenic (grey) 817 °C* 616 °C* Solid 5.78 g/cm3

Antimony (grey) 631 °C 1635 °C Solid 6.69 g/cm3

Bismuth 271 °C 1580 °C Solid 9.75 g/cm3

Images from http://www.theodoregray.com/PeriodicTableDisplay/

Nitrogen ReactivityNitrogen is a very stable, unreactive, diatomic molecule (N2), as it has a

strong triple bond.

N2 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% N2, 21% O2 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.

NitrogenN is an essential element for life, ironically most organism cannot utilize

elemental nitrogen (N2), 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

- N2 and H2 are combined in the presence of catalyst at a high T (400 oC)

and P (~200 bar):

- The reaction is forced forward

removing NH3 as it is produced

by cooling it to a liquid. Why?

- NH3 condenses at a much

higher temperature than N2 or

H2. Why?

- The unreacted N2 and H2 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:

NH3(aq) is often referred to as NH4OH(aq),as the

equilibrium is reactant favoured, NH3(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 N2(g) is such a stable

molecule that reactions producing it tend to

be very exothermic. e.g. azides (N3- salts),

nitrates (TNT & nitrocellulose)

Phosphorus• There are two major allotropes of

phosphorus:– i) White phosphorus (P4) 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) isformed when white phosphorus is heated to200 - 400 oC away from air.

– iii) Black phosphorus and violet phosphorus alsoexist. They are both network solids.

Phosphorus• As we saw in the halogens section,

phosphorus reacts with the halogens• to make PX3 which, on reaction with

more halogen, makes PX5.

It isn’t surprising that P4 is so reactive given its structure. Compare the

bond angles in P4 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 P4O6 and P4O10.

• What is formed when each reacts with water?

Do you remember what was unusual about phosphorous acid?

Phosphorus• Phosphoric acid can polymerize.i) H3PO4 is “orthophosphoric acid”

ii) ii) Two H3PO4 combine as “diphosphoric acid” (or “pyrophosphoric acid” or phosphoester) releasing a molecule of water:

• ii) When a third molecule of H3PO4 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.