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Chemical Ideas 11.2

Chemical Ideas 11.2. The s block: Groups 1 & 2. The s block: Groups 1 & 2. The s block contains two groups of reactive metals. Group 1 metals (alkali metals) Group 2 metals (alkali earth metals)

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Chemical Ideas 11.2

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  1. Chemical Ideas 11.2 The s block: Groups 1 & 2 produced by Dan Dean Bramcote Hills Science Department

  2. The s block: Groups 1 & 2 • The s block contains two groups of reactive metals. • Group 1 metals (alkali metals) • Group 2 metals (alkali earth metals) • Elements become more metallic as you go down a group – for this reason most reactive metals are found at the bottom of the groups • Elements become less metallic as you go across a period from left to right – for this reason Gp 1 metals are more reactive than Gp 2 metals in the same period produced by Dan Dean Bramcote Hills Science Department

  3. Physical properties • S block are only really typical metals in there chemical properties • Metals are not widely used in element form as the more familiar d – block metals Tend to be • Soft • Weak • Low melting points • Too reactive with water and oxygen to have many uses • Compounds of s-block elements are very important produced by Dan Dean Bramcote Hills Science Department

  4. Chemical reactions • Group 1 & 2 metals are all v. reactive • Never found in nature in there native, uncombined state • Compounds of s block metals are very common throughout nature • A lot of the ground beneath our feet in made from compounds of Ca and Mg! produced by Dan Dean Bramcote Hills Science Department

  5. Chemical reactions • Group 1 & 2 show patterns of reactivity as you go down the group • There are similarities between the reaction of the elements in the group, also differences these difference show up in patterns or trends • The similarities are because elements in the same group have the same number of e’s in the outer shell • Difference’s are because as you go down a group the size of the atom increases. produced by Dan Dean Bramcote Hills Science Department

  6. Some chemical properties of Group 2 elements and their compounds • Magnesium, calcium, Strontium and Barium are most well known • Elements are all reactive • Form compounds containing ions with a +2 charge such as Mg2+ and Ca2+ produced by Dan Dean Bramcote Hills Science Department

  7. Reactions of group 2 elements with water • All react with water to form hydroxides and hydrogen • Steady increase in reactivity as you go down group • Mg reacts slowly even when water is heated • Ba reacts rapidly • None react as vigorously as Gp 1 metals • General equation: M(s) + 2H20 (l) M(OH)2 (aq) + H2 (g) produced by Dan Dean Bramcote Hills Science Department

  8. Oxides and hydroxides • General formula of the oxides is MO • General formula of the hydroxides is M(OH)2 • In water, oxides and hydroxides form alkaline solutions (although not very soluble) • Typical of metals, unlike non-metals whose oxides form acidic solutions • Strongest alkaline solutions are formed by elements at bottom of group • Oxides and hydroxides react with acids to form salts MO (s) + 2HCl (aq) MCl2(aq) + H20 (l) M(OH)2 (s) + H2SO4(aq)  MSO 4(aq) + 2H20 (l) • This neutralising effect is used by farmers when they put lime (calcium hydroxide) on their fields to neutralise soil acidity produced by Dan Dean Bramcote Hills Science Department

  9. Effect of heating carbonates • The general formula of Gp 2 carbonates is MCO3 • Heating carbonates makes them decompose, forming the oxide and releasing carbon dioxide MCO3 (s)  MO (s) +CO 2(g) • Carbonates more difficult to decompose the further you go down the group • We say the thermal stability of calcium carbonate is greater than that of magnesium carbonate • Decomposition of calcium carbonate (limestone) is an important process used to manufacture calcium oxide (quicklime) produced by Dan Dean Bramcote Hills Science Department

  10. Solubility of compounds Solubility of hydroxides • More soluble as you go down the group • Pattern is repeated for most Gp 2 compounds where the negative ion has a single charge (1-) Solubility of carbonates • Less soluble as you go down the group • Pattern is repeated for most Gp 2 compounds where the negative ion has a double charge (2-) produced by Dan Dean Bramcote Hills Science Department

  11. Solubility of compounds • Numbers in table don’t show a perfect trend • This rule is generally correct but and is useful in making predictions • As in all science the predictions can’t be confirmed until you or someone else confirms it through experiments produced by Dan Dean Bramcote Hills Science Department

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