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© Boardworks Ltd 2003 THE ALKALI METALS
© Boardworks Ltd 2003 Alkali metals and the Periodic Table These are the alkali metals or Group 1 Elements. H Li Na K Rb Cs Fr Be ScTi Mg VCrMnFeCoNiCuZnGaGeSeBrCaKr YZrNbMoTcRuPdAgCdInSnSbSrTeRh BaHfTaWReOsIrAuHgTlPbBiPoLaAtPt RaRfDbSgBhHsMt??Ac? AlP NO SCl FNe Ar Rn I Si Xe He BC As Li Na K Rb Cs Fr
© Boardworks Ltd 2003 Electronic Structure All the Group 1 elements have 1 electron in the outermost shell. Li Na K Rb Cs Lithium Sodium Potassium Rubidium Caesium 2,8,1 2,8,8,1 2,1
© Boardworks Ltd 2003 Trends in Density Lithium, sodium and potassium are all less dense than water and so will float. Densities follow a general, although not perfect, trend. ElementSymbolDensity LithiumLi0.53 SodiumNa0.97 PotassiumK0.86 RubidiumRb1.53 CaesiumCs1.88
© Boardworks Ltd 2003 Melting Points The atoms in the Group 1 elements are bonded together using just one outer shell electron per atom. As a result, melting points are low compared to most metals. ElementMelt. Point (C) Lithium181 Sodium98 Potassium Rubidium39 Caesium Can you predict the missing data? 63 29
© Boardworks Ltd 2003 Trends in Chemical Reactivity Reactivity increases down the group. Reactions all involve the loss of the outermost electron which changes the metal atom into a metal 1+ ion. Losing this electron seems to get easier as we go down the group. Li Na K Rb Cs Reactivity Increases
© Boardworks Ltd 2003 Reactivity and Electron Structures 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 Increases
© Boardworks Ltd 2003 Reaction with Water 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’. Reaction of Lithium H H O H H O H H Li + + H O - H O -
© Boardworks Ltd 2003 Reaction of Lithium with Water Lithium fizzes quickly in water forming lithium hydroxide and hydrogen. Lithium + water Lithium hydroxide + hydrogen 2Li(s) + 2H 2 O(l) 2LiOH(aq) + H 2 (g) The solution that remains is strongly alkaline.
© Boardworks Ltd 2003 Reaction of Sodium with Water Sodium fizzes very quickly in water. The gas given off can be ignited by a lighted splint. Sodium + water Sodium hydroxide + hydrogen 2Na(s) + 2H 2 O(l) 2NaOH(aq) + H 2 (g) sodium on water enlarged
© Boardworks Ltd 2003 Potassium with Water Lithium fizzes. Sodium reacts more vigorously. What will potassium do? Potassium + water 2K(s) + 2H 2 O(l) Potassium hydroxide + hydrogen 2KOH(aq) + H 2 (g) What will the word equation and chemical equations be for the reaction of potassium with water? Potassium + water
© Boardworks Ltd 2003 The Group 1 Metals and oxygen The Group 1 elements burn in air to form metal oxides. Don’t try to put them out with water! Lithium + oxygen Lithium Oxide 4Li (s) + O 2 (g) 2 Li 2 O (s) What will the word equation and chemical equations be for the reaction of sodium with air? Sodium + oxygen Na(s) + O 2 (g) sodium oxide 2Na 2 O (s) 4
© Boardworks Ltd 2003 The Group 1 Metals and chlorine The Group 1 elements burn in chlorine to form metal chlorides. Lithium + chlorine Lithium chloride 2Li (s) + Cl 2 (g) 2 LiCl (s) What will the word equation and chemical equations be for the reaction of sodium with chlorine? Sodium + chlorine Na(s) + Cl 2 (g) Sodium chloride 2NaCl (s) 2
© Boardworks Ltd 2003 Uses of the Group 1 Metals 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
© Boardworks Ltd 2003 Using sodium to transfer heat 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. 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.
© Boardworks Ltd 2003 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.
© Boardworks Ltd 2003 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.
© Boardworks Ltd 2003 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.
© Boardworks Ltd 2003 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?
© Boardworks Ltd 2003 Dr Ivan Idea Syndicate 2 Some data on the metals that melt below 500 o C.
© Boardworks Ltd 2003 How many electrons do the alkali metals have in their outer shell? A.1 B.2 C.4 D.7
© Boardworks Ltd 2003 What charge ions are formed by the alkali metals? A.4 B.3 C.2 D.1
© Boardworks Ltd 2003 Which answer places the alkali metals in order of increasing reactivity? A. Na, Li, K, B. K, Na, Li C. Li, Na, K D. Li, K, Na
© Boardworks Ltd 2003 When alkali metals react with water we get: A.Hydrogen + a metal oxide B.Oxygen + a metal oxide C.Hydrogen + a metal hydroxide D.Oxygen +a metal hydroxide
© Boardworks Ltd 2003 What will the melting point of caesium be? A.-10 o C B. 0 o C C. 25 o C D. 38 o C
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