The s -Block Elements

1. 40 The s-Block Elements 40.1 Characteristic Properties of the s-Block Elements 40.2 Variation in Properties of the s-Block Elements 40.3 Variation in Properties of the Compounds of the s-Block Elements

2. The s-Block Elements • Elements of Groups IA* (the alkali metals) and IIA* (the alkaline earth metals) •  constitute the s-block elements •  their outermost shell electrons are in the s orbital • *Note: In the following, Groups IA and IIA are abbreviated as Groups I and II respectively.

3. The s-Block Elements • The two groups of elements have many similarities • highly reactive metals • strong reducing agents •  form ionic compounds with fixed oxidation states of +1 for Group I elements and +2 for Group II elements

4. The s-block elements

5. Group I elements • Lithium

6. Group I elements • Sodium

7. Group I elements • Potassium

8. Group I elements • Rubidium

9. Group I elements • Francium

10. Group I elements • Beryllium

11. Group I elements • Magnesium

12. Group I elements • Calcium

13. Group I elements • Strontium

14. Group I elements • Barium

15. Group I elements • Radium

16. 40.1 Characteristic Properties of thes-Block Elements

17. 40.1 Characteristic Properties of the s-Block Elements (SB p.38) Some characteristic properties of Group I elements

18. 40.1 Characteristic Properties of the s-Block Elements (SB p.38) Some characteristic properties of Group I elements

19. 40.1 Characteristic Properties of the s-Block Elements (SB p.38) Some characteristic properties of Group II elements

20. 40.1 Characteristic Properties of the s-Block Elements (SB p.38) Some characteristic properties of Group II elements

21. 40.1 Characteristic Properties of the s-Block Elements (SB p.38) Metallic Character • All Group I elements •  silvery solids and tarnish rapidly in air at room temperature and pressure •  stored under paraffin oil or in vacuum-sealed ampoules • (to prevent contact with oxygen and water vapour in air)

22. 40.1 Characteristic Properties of the s-Block Elements (SB p.38) Metallic Character • All Group I elements •  weakmetallic bonds •  only one valence electron per atom delocalized into the electron sea for the formation of metallic bonds •  soft and can be cut with a knife easily

23. 40.1 Characteristic Properties of the s-Block Elements (SB p.38) Metallic Character • All Group I elements •  low melting points and boiling points

24. 40.1 Characteristic Properties of the s-Block Elements (SB p.39) sodium Sodium is stored under paraffin oil

25. 40.1 Characteristic Properties of the s-Block Elements (SB p.39) caesium rubidium Caesium and rubidium are stored in vacuum-sealed ampoules

26. 40.1 Characteristic Properties of the s-Block Elements (SB p.39) Metallic Character • All Group I elements •  body-centred cubic structures •  much empty space •  comparatively low densities

27. 40.1 Characteristic Properties of the s-Block Elements (SB p.39) Some information about Group I elements

28. 40.1 Characteristic Properties of the s-Block Elements (SB p.39) Some information about Group I elements

29. 40.1 Characteristic Properties of the s-Block Elements (SB p.39) Metallic Character • All Group II elements • greyish solids at room temperature and pressure •  also be cut with a knife, but harder than the alkali metals

30. 40.1 Characteristic Properties of the s-Block Elements (SB p.39) Metallic Character • All Group II elements •  two valence electrons per atom •  smaller atomic sizes •  metallic bonds are stronger

31. 40.1 Characteristic Properties of the s-Block Elements (SB p.39) Metallic Character • All Group II elements •  the melting points and boiling points are higher than those of Group I elements •  show different metallic structures

32. 40.1 Characteristic Properties of the s-Block Elements (SB p.39) Metallic Character • Beryllium and magnesium • hexagonal close-packed structures

33. 40.1 Characteristic Properties of the s-Block Elements (SB p.39) Metallic Character • Calcium and strontium • face-centred cubic structures

34. 40.1 Characteristic Properties of the s-Block Elements (SB p.39) Metallic Character • Barium •  body-centred cubic structure

35. 40.1 Characteristic Properties of the s-Block Elements (SB p.40) Some information about Group II elements

36. 40.1 Characteristic Properties of the s-Block Elements (SB p.40) Some information about Group II elements

37. 40.1 Characteristic Properties of the s-Block Elements (SB p.40) Low Electronegativity • All s-block elements • low electronegativity values

38. 40.1 Characteristic Properties of the s-Block Elements (SB p.40) Low Electronegativity • All s-block elements • electropositive elements •  their atoms have a relatively high tendency to lose their outermost shell electrons

39. 40.1 Characteristic Properties of the s-Block Elements (SB p.40) Low Electronegativity • The outermost shell electrons • effectively shielded from the nucleus by the fully-filled inner electron shells •  the outermost shell electrons are only loosely held by the nucleus

40. 40.1 Characteristic Properties of the s-Block Elements (SB p.40) Low Electronegativity • Going down both Groups I and II • the elements become more electropositive • the atoms tend to lose electrons more readily •  the outermost shell electrons are much further away from the nucleus

41. Let's Think 1 40.1 Characteristic Properties of the s-Block Elements (SB p.40) Low Electronegativity • Group II elements • more electronegative than the Group I elements •  the increase in effective nuclear charge •  the attractive force between the nucleus and the outermost shell electrons becomes stronger

42. 40.1 Characteristic Properties of the s-Block Elements (SB p.40) Electronegativity values of Groups I and II elements

43. 40.1 Characteristic Properties of the s-Block Elements (SB p.41) Formation of Basic Oxides 1. Group I Elements • All alkali metals form more than one type of oxide on burning in air (except lithium)

44. 40.1 Characteristic Properties of the s-Block Elements (SB p.41) 1. Group I Elements • Three types of oxides: • normal oxides • peroxides • superoxides

45. 40.1 Characteristic Properties of the s-Block Elements (SB p.41) 1. Group I Elements • They are all ionic • They can be related as follows: O2– oxide ion O22–peroxide ion 2O2–superoxide ion

46. 4Li(s) + O2(g) 2Li2O(s) lithium oxide 40.1 Characteristic Properties of the s-Block Elements (SB p.41) 1. Group I Elements • Lithium •  when it is burnt in air, it forms normal oxide only

47. 4Na(s) + O2(g) 2Na2O(s) sodium oxide 4Na2O(s) + O2(g) 2Na2O2(s) sodium peroxide 40.1 Characteristic Properties of the s-Block Elements (SB p.41) 1. Group I Elements • Sodium •  when it is burnt in an abundant supply of oxygen •  forms both the normal oxide and the peroxide

48. 40.1 Characteristic Properties of the s-Block Elements (SB p.41) 1. Group I Elements • Potassium, rubidium and caesium •  form the normal oxide, the peroxide and superoxides when they are burnt in air

49. 40.1 Characteristic Properties of the s-Block Elements (SB p.41) 1. Group I Elements • Potassium: • 4K(s) + O2(g)  2K2O(s) potassium oxide • 2K2O(s) + O2(g)  2K2O2(s) potassium peroxide • K2O2(s) + O2(g)  2KO2(s) potassium superoxide

50. 40.1 Characteristic Properties of the s-Block Elements (SB p.41) 1. Group I Elements • Rubidium: • 4Rb(s) + O2(g)  2Rb2O(s) • 2Rb2O(s) + O2(g)  2Rb2O2(s) • Rb2O2(s) + O2(g)  2RbO2(s)