2. Nitrogen is a non-metal at the top of Group 5. It forms 78% of the atmosphere and is used in the manufacture of ammonia.

3. Phosphorus is also a non-metal. It is used in matches, fertilisers and detergents.

4. Arsenic is a metalloid, a metal with some non-metal character. It is used in the manufacture of computer chips.

5. Antimony is also a metalloid. It is alloyed with lead for use in car batteries, and antimony compounds are used as flame retardants for plastics and textiles.

6. Bismuth is a metal used in low melting point alloys for fire sprinkler valves. Bismuth compounds may be used to provide the shine in lipsticks.

7. Group 5 is in the centre of the p block in the periodic table.

8. Atoms of Group 5 elements can form three covalent bonds by sharing their three unpaired electrons.

9. The oxidation state of the Group 5 element in the compounds formed is +3 or –3.

10. Atoms of Group 5 elements can also form a dative covalent bond by sharing a lone pair of electrons.

11. The oxidation state of the Group 5 element in the compounds formed is +5.

12. Nitrogen gas molecules are diatomic. They each comprise two nitrogen atoms covalently bonded together.

13. Nitrogen gas molecules are diatomic. They each comprise two nitrogen atoms covalently bonded together.

14. This is a dot and cross diagram to show the bonding in a nitrogen molecule. Each nitrogen atom shares three electrons.

15. This is a dot and cross diagram to show the bonding in a nitrogen molecule. Each nitrogen atom shares three electrons.

16. The bond enthalpy of the N=N is +945 kJ mol –1. This is very large, so most reactions involving nitrogen molecules have high activation enthalpies, and need high temperatures and catalysts to occur.

17. Ammonia is nitrogen hydride, NH 3. It is a gas at room temperature and it readily dissolves in water to form ammonia solution.

18. This is a dot and cross diagram to show the bonding in an ammonia molecule. Again, each nitrogen atom shares three electrons.

19. Ammonia has a lone pair of electrons. It can form dative covalent bonds with hydrogen ions and with transition metal ions, where it acts as a ligand in complex ions.

20. Ammonia has a lone pair of electrons. It can form dative covalent bonds with hydrogen ions and with transition metal ions, where it acts as a ligand in complex ions.

21. Ammonia has a lone pair of electrons. It can form dative covalent bonds with hydrogen ions and with transition metal ions, where it acts as a ligand in complex ions.

22. Ammonia has a lone pair of electrons. It can form dative covalent bonds with hydrogen ions and with transition metal ions, where it acts as a ligand in complex ions.

23. Ammonia acts as a base and forms dative covalent bonds with hydrogen ions, H +, to form the ammonium ion.

24. Ammonia acts as a base and forms dative covalent bonds with hydrogen ions, H +, to form the ammonium ion.

25. Ammonia acts as a base and forms dative covalent bonds with hydrogen ions, H +, to form the ammonium ion.

26. This is another way to show the bonding in the ammonium ion.

27. As all four bonds in the ammonium ion are equivalent once formed, it is usual to show the bonding in the ammonium ion like this.

28. Nitrogen forms several oxides. They are all gases and are sometimes collectively represented as NO x.

29. Dinitrogen oxide is a colourless gas produced from nitrogen monoxide by denitrifying bacteria in the soil.

30. Nitrogen monoxide is a colourless gas produced from nitrate(III) ions by denitrifying bacteria in the soil. It is also produced in vehicle engines and during thunderstorms.

31. Nitrogen dioxide is a toxic brown gas produced when nitrogen monoxide oxidises in the atmosphere.

32. Nitrate(III) ions can be formed from ammonium ions by Nitrosomonas bacteria in the soil. This is the dot and cross diagram for the nitrate(III) ion.

33. The diagram can be simplified.

34. The single negative charge on the ion is delocalised over the two N–O bonds, which are equivalent.

35. Nitrate(V) ions can be formed from nitrate(III) ions by Nitrobacter bacteria in the soil. This is the dot and cross diagram for the nitrate(V) ion.

36. The oxidation state of nitrogen is increased from +3 to +5 because the lone pair of electrons forms a dative covalent bond with an oxygen atom.

37. The single negative charge on the ion is delocalised over the three N–O bonds, which are equivalent.

38. The nitrate(III) ion is often called nitrite. It can be formed from the nitrate(V) ion by anaerobic denitrifying bacteria in the soil.

39. The nitrate(V) ion is often just called nitrate. The Roman numerals in brackets give us the oxidation states of nitrogen in these ions.