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Group 2

Group 2. The ‘S’ block elements. Each alkaline earth metal is denser and harder. and has a higher melting point than the alkali metal in the same period. Alkaline Earth Metals. Next to the alkali metals are the alkaline earth metals.

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Group 2

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  1. Group 2 The ‘S’ block elements

  2. Each alkaline earth metal is denser and harder and has a higher melting point than the alkali metal in the same period. Alkaline Earth Metals • Next to the alkali metals are the alkaline earth metals. • Alkaline earth metals are reactive, but not as reactive as the alkali metals. • Groups 2 are always found in nature combined with other elements. • They’re called active metals because of their readiness to form new substances with other elements.

  3. Recall earlier work How would the following vary down group 2 • Electronegativity • Atom radius • Ionic radius • Reactivity • First Ionisation energy • Ionic nature • Electrical conductivities • Melting points • Densities • Hardness • Oxidation numbers

  4. Flame tests Compounds containing lithium, sodium, potassium, calcium and barium can be recognised by burning the compound and observing the colours produced: Sodium Yellow Barium Green Lithium Red Potassium Lilac Calcium Brick red Strontium crimson

  5. Electrons are excited to a higher energy level by the heat When the electrons want to return to their original level they need to get rid of the energy gained Light is emitted of different wavelengths Why do we get different colours?

  6. Group 2 • Observe what happens when Mg and Ca are burned in air • What would you predict for Sr and Be? • How does calcium and magnesium react with water? • What is the general trend for the group? • Why is this? Link the reactivity with ionisation energy/electronegativity/ atomic radius

  7. Reactions with HalidesGroup 2 • Describe what happens when Magnesium is heated and added to chlorine gas? • Write an equation for this • 2Mg(s) + Cl2(g) = MgCl2(s) • What is the general formula? • What is formed and what does it look like? • Is it soluble water? • Are the compounds formed ionic or covalent in character? How can you tell? • Account for the difference in reactivity between the two groups • Conclusion: Beryllium is more covalent as its melting point is less • This is due to it’s charge density

  8. Reactions of the oxides with water and acid • Experiment add MgO and CaO to water. Write down your observations when the oxides are added to water • What is happening, a reaction or simple dissolving? • What do you observe when the oxides are added to acid you will measure the enthalpy change • Write a conclusion

  9. The behaviour of the group 1 and 2 Hydroxides Are the group 1 hydroxides soluble? Can you think of a salt of group 1 that is insoluble? What is the trend with the hydroxides? Can you think of a reason?

  10. Find out what is meant by lattice energy/enthalpy and see which is biggest. Predict which is biggest for each set of data

  11. Consider what you know about the solubility of group 1 and the lattice enthalpy What is the pattern? The bigger the lattice enthalpy the less soluble the compound Conclusion

  12. Now you know the pattern, explain it! Generally the more densely charged the ion the stronger it attracts it opposite. Can you explain the results from the group 2 sulphates (and nitrates do the same thing) We can comment on the lattice energy… Why is it bigger? What do you know about the size of the sulphate and nitrate ions? The large ion is not stable with a small polarising cation and is very stable with the larger less polarising cation

  13. Recall: what happens when copper carbonate is heated? What is this reaction called? We know transition metals decompose, what about other metal compounds? CuCO3 CuO + CO2 Thermal stability of group 1 and 2 carbonates

  14. Conduct an experiment to see which carbonates break down • How will you know it has decomposed? Results: • Group 1 are thermally stable • There is one exception, which is it? • Explain why it is thermally unstable • All group 2 decompose to form the oxide and carbon dioxide

  15. Recall data: What happens to nitrates when they are heated? What is this reaction called? What is the brown gas called that is produced? Conduct an experiment to see whether all the metals from group 1 and 2 do the same thing This equation is not balanced, see if you can do it. Cu(NO3)2 CuO + NO2 + O2 Thermal decomposition of the nitrates

  16. Results • Group 1 do not form the brown gas, so what is produced instead? • Sodium nitrite • What is the formula for this? • NaNO2 • Equation • NaNO3(s) = NaNO2(s) + O2(g) • What is the ion present? • What is the oxidation number of the nitrogen in this compound?

  17. Results continued… • Which group 1 element did not form nitrite? • Why did it not form nitrite? • What did group 2 nitrates do? • Write an equation • What can you deduce about the size and charge of the cation and thermal stability of the compounds? • System to aid recall • Group 1 1 gas • Group 2 2 gas

  18. Titrations • A fruit can be skinned by adding KOH to it. • After the skin has gone we can work out how much was used by reacting with a known quantity of acid • Design an experiment that will do this. • You need all the chemicals and expert know-how to limit the errors involved.

  19. Use an acid of known strength. HCl prepared using a volumetric flask. • Use pipette and burette. • What do you need to do to the burette before using it? • Make sure it is parallel –why? • Make sure the tap is not dripping • Make sure the funnels is not in the top

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