THE ALKALI METALS

1. THE ALKALI METALS

2. These are the alkali metals or Group 1 Elements Li Na K Rb Cs H He Fr Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac Rf Db Sg Bh Hs Mt ? ? ? Alkali metals and the Periodic Table

3. All the Group 1 elements have 1 electron in the outermost shell. 2,1 2,8,1 2,8,8,1 Electronic Structure Li Lithium Na Sodium K Potassium Rb Rubidium Cs Caesium

4. Lithium, sodium and potassium are all less dense than water so will float. Densities follow a general, although not perfect, trend. Trends in Density

5. The atoms in the Group 1 elements are bonded together using just 1 outer shell electron per atom. As a result melting points are low compared to most metals. Activity Melting Points 63 29 Can you predict the missing data?

6. Reactivity increases down the group. Reactions all involve loss of the outermost electron which changes the metal atom into an metal 1+ ion. So, losing this electron seems to get easier as we go down the group. Li Na K Rb Cs Trends in Chemical Reactivity Reactivity Increases

7. 1. The outer electron (-) gets further from the nucleus (+) as you go down the group. This reduces the force of attraction. 2. The inner shells ‘shield’ the outermost electron from the attraction from the nucleus. Both factors make it easier to lose the outer electron as you go down the group. Reactivity and Electron Structures Reactivity Increases

8. The Group 1 elements all react vigorously with water. Hydrogen gas is produced which sometimes catches fire. An alkali is left behind in the solution which is why these elements are often called The Alkali Metals Li Li H H H H O O - + O H H Li H + - H O Li Reaction with Water Eg. Reaction of Lithium

9. Lithium fizzes quickly in water forming lithium hydroxide and hydrogen Reaction of Lithium with Water Lithium + water g Lithium hydroxide + hydrogen 2Li(s) + 2H2O(l)  2LiOH(aq) + H2(g) • The solution that remains is strongly alkaline.

10. Sodium fizzes very quickly in water catching fire if not allowed to move around. sodium on fire in water Sodium on water Enlarged Reaction of Sodium with Water Sodium + water g Sodium hydroxide + hydrogen 2Na(s) + 2H2O(l)  2NaOH(aq) + H2(g)

11. Lithium fizzes. Sodium reacts more vigorously. What will potassium do? Activity Potassium + water Potassium + water  Potassium with Water What will the word equation and chemical equations be for the reaction of potassium with water? Potassium hydroxide + hydrogen 2KOH(aq) + H2(g) 2K(s) + 2H2O(l) 

12. The Group 1 elements burn in air to form metal oxides. Don’t try to put them out with water! Activity Sodium + oxygen  Lithium + oxygen  Lithium Oxide The Group 1 Metals and oxygen: 4Li (s) + O2(g)  2 Li2O (s) • What will the word equation and chemical equations be for the reaction of sodium with air? sodium oxide 2Na2O (s) 4 Na(s) + O2 (g) 

13. The Group 1 elements burn in chlorine to form metal chlorides. Activity Sodium + chlorine  Lithium + chlorine  Lithium chloride The Group 1 Metals and chlorine 2Li (s) + Cl2(g)  2 LiCl (s) • What will the word equation and chemical equations be for the reaction of sodium with chlorine? Sodium chloride 2NaCl (s) 2 Na(s) + Cl2 (g) 

14. The metals themselves are too reactive to have many uses although sodium vapour gives street lights their yellow glow. Lithium metal is used to improve the strength of aircraft alloys and is also used in some electrical batteries. Common sodium compounds include “salt”, (sodium chloride), “bicarbonate” (sodium hydrogen carbonate), washing soda (sodium carbonate) and caustic soda (sodium hydroxide.) Potassium compounds are used in “NPK fertilisers”, in weedkillers, explosives and many other chemicals. Sodium light potassium Uses of the Group 1 Metals

15. The activity Following an accident at a nuclear power station three groups are represented at a public meeting. The debate centres around an accident involving a spill of molten sodium metal which was being used to cool the reactor. It needs to include: The benefits of using sodium to transfer heat and the fact that risks resulting from chemical reactivity are containable. The chemical reactivity of sodium and the fact that if containment did fail the whole power station could blow up. Whether there are other safer metals that could be used in place of sodium. 3 groups prepare presentations. Others students devise questions to follow the presentations. Activity Using Sodium to Transfer Heat

16. The Incident Most power stations burn a fossil fuel and use water to transfer heat from the burners to the turbine area. An alternative to water is sodium. Although solid it melts fairly easily and is a better conductor of heat than water. This has prompted its use as a coolant to absorb and transfer the heat produced in nuclear power stations. To Japan, a country with no fossil fuels, nuclear power is particularly attractive. However, in 1996 Japan’s nuclear industry suffered a setback when a split in a stainless steel pipe spewed 3 tonnes of molten sodium over the reactor floor. Nuclear representatives say there was no radiation leak and opponents to nuclear power were whipping up public concern. Anti-nuclear protestors say that had it leaked underneath the floor the entire nuclear station would have been at risk. The government agreed to make plans about how to deal with a nuclear accident just in case one did ever happen. (It’s true!) Activity

17. Nuclear Industry Representatives group Make a case as to why Japan must have nuclear power. Spell out the very low accident rate in the industry. Explain why a liquid that can absorb heat better is a good thing (safer?) for a nuclear reactor. Spell out the fact that you understand the common reactions of sodium and had already set in place systems to prevent these reactions being a danger. Make clear that there is no totally safe way of generating energy and that use of fossil fuels also entails accidents and guaranteed pollution. Activity

18. Anti-Nuclear Protest group Explain that risk assessment must take account both of the chances of an accident and the impact of that accident. Leaked long lasting radioactive material or even melt-down and nuclear explosion! Challenge the use of sodium (rather than larger volumes of water) as representing a needless risk. Spell out in detail the possibility of explosive reactions involving sodium and potentially devastating outcomes. Other fuels are available even if they have to be imported. Activity

19. Dr Ivan Idea Syndicate One of the main reasons for using sodium is that it melts easily and, as a metal, it conducts heat well. Check out the melting point, reactivity and toxicity of other metals and consider the feasibility of using them. Are there particular risks you would need to guard against? Can you suggest ways to minimise these? Or - should you just go back to using water for heat transfer? Activity

20. Dr Ivan Idea Syndicate 2 Some data on the metals that melt below 500oC Activity

21. How many electrons do the alkali metals have in their outer shell? 1 2 4 7

22. What charge ions are formed by the alkali metals? 4 3 2 1

23. Which answer places the alkali metals in order of increasing reactivity? Na, Li, K, K, Na, Li Li, Na, K Li, K, Na

24. When alkali metals react with water we get: Hydrogen + a metal oxide Oxygen + a metal oxide Hydrogen + a metal hydroxide Oxygen +a metal hydroxide

25. What will the melting point of caesium be? -10oC B. 0oC C. 25oC D. 38oC