Group 1 Elements: Reactivity Trend and Chemical Properties

1. PERIODIC TABLE OF ELEMENTS Group 1 4S1 Thursday, 14/4/2011 7.30 – 8.40 am

2. Members of Group 1 Lithium, Li (2.1) Sodium, Na (2.8.1) Potassium, K (2.8.8.1) Caesium, Cs Rubidium, Rb Francium, Fr

4. Trend of change in the physical properties • Atomic radius (atomic size) • - increases down the group • - bcoz number of shells • occupied with electrons • increases down the group

5. 2. Low density - however, density increases slowly down the group - bcoz increase in mass is bigger compared to increase in volume when going down the group

6. 3. Mp & bp decreases down the group - as atomic size increases down the group, the metallic bonding btwn atoms of alkali metals becomes weaker - less E is needed to overcome the weaker metallic bonding during melting & boiling when going down the group

7. CHEMICAL PROPERTIES • same group  exhibit same chemical props • all alkali metals are very reactive Li Na K Cs Rb Fr More reactive • reactivity of alkali metal is measured by the ease of its atom to lose its single valence e- to achieve duplet / octet arrangement

8. Explanation for the increase in reactivity down Group 1: • all alkali metals have 1 valence e- & will release this e- during chem rxn to achieve stable duplet/octet arrangement • when going down the group, atomic size increases. the single valence e- becomes further away from the nucleus

9. this causes the single valence e- to be more weakly pulled by the nucleus • thus, the single valence e- can be released more easily down the group • as a result, reactivity of alkali metals increases down the group Single valence e-

10. Reaction of Li with H2O 2Li + 2H2O  2LiOH + H2

11. Reaction of Na with H2O 2Na + 2H2O  2NaOH + H2

12. Reaction of K with H2O 2K + 2H2O  2KOH + H2

13. Reaction of Alkali Metals with O2 H2O

14. Reaction of Alkali Metals with O2

15. Reaction of Alkali Metals with O2 4Li + O2 2Li2O Li2O + H2O  2LiOH 4Na + O2 2Na2O Na2O + H2O  2NaOH 4K + O2 2K2O K2O + H2O  2KOH

16. Reaction of Alkali Metals with Cl2

17. Reaction of Alkali Metals with Cl2

18. Reaction of Alkali Metals with Cl2 2Li + Cl2 2LiCl 2Na + Cl2 2NaCl 2K + Cl2 2KCl

19. Reaction of Alkali Metals with Br2

20. Reaction of Alkali Metals with Br2

21. Reaction of Alkali Metals with Br2 2Li + Br2 2LiBr 2Na + Br2 2NaBr 2K + Br2 2KBr

22. Safety Precautions in Handling Group 1 Metals • alkali metals are kept in paraffin oil to avoid contact with O2 & H2O vapour in air • wear safety gloves & goggles • don’t touch with bare hands

23. PERIODIC TABLE OF ELEMENTS Group 17 4S1 Monday, 18/4/2011 10.45 – 11.55 am

24. Members of Group 17 • Fluorine, F (2.7) • Chlorine, Cl (2.8.7) • Bromine, Br • Iodine, I • Astatine, At

25. Group 17 elements • also known as the ‘halogens’ Greek word, means ‘salt former’

27. Colour of Halogens D A R K E R

28. Trend of change in the physical properties • Atomic radius (atomic size) • - increases down the group • - bcoz number of shells • occupied with electrons • increases down the group

29. 2. Low mp & bp - the atoms are held together by weak van der Waals force of attraction - only little heat E is required to overcome the forces during melting & boiling

30. 3. Mp & bp increases down the group - bcoz molecular size increases down the group. - thus, van der Waals forces of attraction btwn halogen molecules become stronger - more E is needed to overcome the stronger forces of attraction during melting & boiling

31. 4. Low density - however, density increases slowly down the group - bcoz increase in mass is bigger compared to increase in volume when going down the group

32. Electronegativity of Halogens • all halogens have high electronegativity • most electronegative element = F

33. (Cont.) Electronegativity of Halogens • Electronegativity decreases down the group • - bcoz no. of shells occupied by e-(s) increases when going down the group • - causes the outermost occupied shell to be further away fr the nucleus • - strength of nucleus to attract e-(s) becomes weaker

34. CHEMICAL PROPERTIES • same group  exhibit same chemical props F2 Cl2 Br2 I2 At2 Less reactive • reactivity of halogen is measured by the ease of its atom to gain 1 e- to achieve duplet / octet arrangement • the easier to gain e-, the more reactive the halogen is

35. Explanation for the decrease in reactivity • all halogens have 7 valence e- • each atom will gain 1 e- to be stable. • ion with -1 charge is formed • when going down the group, the atomic size increases. Outermost occupied shell gets further away fr the nucleus • strength of nucleus to attract 1 more e- decreases fr fluorine  astatine • hence, reactivity decreases down the group

36. Halogens as Oxidizing Agents • good oxidizing agent • strength as oxidizing agent decreases down the group bcoz reactivity decreases down the group

38. Reaction of Cl2 with H2O Observation: greenish-yellow gas dissolves rapidly in H2O to produce pale yellow solution. This solution turns red litmus paper  blue  white Result: Cl2 + H2O HCl + HClO

39. Reaction of Br2 with H2O Observation: reddish-brown liq. dissolves slowly in H2O to form yellowish-brown solution. This solution turns red litmus paper  blue  white Result: Br2 + H2O HBr + HBrO

40. Reaction of I2 with H2O Observation: only a very small amount of the purplish-black solid dissolves very slowly in water to form a pale yellow solution. This solution has no effect on blue litmus paper Result: I2 + H2O HI + HIO

41. Reaction of Cl2 with Fe

42. (Cont.) Reaction of Cl2 with Fe Observation: Hot iron wool ignites rapidly with a bright flame. A brown solid is formed Result: 2Fe + 3Cl2 2FeCl3 Brown solid

43. Reaction of Br2 with Fe

44. (Cont.) Reaction of Br2 with Fe Observation: Hot iron wool glows moderately bright, moderately fast & less vigorously. A brown solid is formed Result: 2Fe + 3Br2 2FeBr3 Brown solid

45. Reaction of I2 with Fe

46. (Cont.) Reaction of I2 with Fe Observation: Hot iron wool glows dimly & softly. A brown solid is formed. Result: 2Fe + 3I2 2FeI3 Brown solid

47. Reaction of Cl2 with NaOH

48. (Cont.) Reaction of Cl2 with NaOH Observation:Greenish-yellowgas dissolves rapidly in NaOH solution to produce a colourless solution Result: Cl2 + 2NaOH  NaCl + NaOCl + H2O

49. Reaction of Br2 with NaOH

50. (Cont.) Reaction of Br2 with NaOH Observation:Reddish-brownliquid dissolves moderately fast in NaOH solution to produce a colourless solution Result: Br2 + 2NaOH  NaBr + NaOBr + H2O