Group 2

    Cards (26)

      • elements in group 2 called the alkaline earth metals
      • these are reactive
      • all of the elements in group 2 have two electrons in the s subshell of their outer shell
      • when group 2 elements react, these two outer electrons are lost
      • by transferring these electrons to other species, group 2 metals act as reducing agents
    • Mg  Mg2++Mg\ \rightarrow\ Mg^{2+}+2e2e^-
      • when magnesium reacts, it loses two outer electrons to form magnesium ions - oxidised
      • these can then be transferred to a different chemical species called X, which is being reduced
      • magnesium is acting as a reducing agent
    • Why does the reactivity of group 2 metals increase down the group?
      They lose their outer 2 electrons to react
    • What is ionisation energy?
      Energy required to remove an electron from an atom
    • How do group 2 metals react in terms of ionisation energy?
      They require first and second ionisation energy
    • What happens to the first and second ionisation energy as we go down group 2?
      They decrease down the group
    • What causes the greater atomic radius in group 2 metals as you go down the group?
      Two outer electrons are further from the nucleus
    • What effect do more inner electron shells have on outer electrons in group 2 metals?
      They shield outer electrons from the nucleus' positive charge
    • How does the attraction of outer electrons to the nucleus change down group 2?
      Outer electrons are less strongly attracted to the nucleus
    • What is the relationship between ionisation energy and the energy required to remove electrons down group 2?
      It takes less energy to remove electrons down the group
    • How does the trend in ionisation energy affect reactivity in group 2 metals?
      As ionisation energy decreases, reactivity increases
    • reaction of group 2 metals with oxygen
      • if we heat magnesium in air then the magnesium reacts with oxygen forming a bright white light
      • 2Mg +2Mg\ +O2  2MgOO_2\ \rightarrow\ 2MgO
    • reaction of group 2 metals with water
      • magnesium reacts very slowly with cold water,
      • as we move down group 2 the elements react much more rapidly
      • Ca(s) +Ca(s)\ +2H2O (l)  Ca(OH)2 (aq) +2H_2O\ (l)\ \rightarrow\ Ca\left(OH\right)_2\ (aq)\ +H2 (g)H_2\ (g)
      • produces the alkaline metal hydroxide and hydrogen gas
    • forming group 2 hydroxides
      CaO (s) +CaO\ (s)\ +H2O (l)  Ca(OH)2 (aq)H_2O\ (l)\ \rightarrow\ Ca\left(OH\right)_2\ (aq)
      • as calcium hydroxide forms, it dissolves in water to form calcium hydroxide solution
      • however calcium hydroxide solution is only slightly soluble in water, so this solution very quickly becomes saturated
      • as we continue to form calcium hydroxide this no longer dissolves but instead it forms solid calcium hydroxide
    • solubility
      • solubility of group 2 hydroxides increases going down the group - goes from extremely high to relatively soluble
      • explains alkalinity of group 2 hydroxides - how alkalinity increases going down the group
      • when group 2 hydroxides dissolve in water, they release the metal ion and two hydroxide ions - aq hydroxide ions make solution alkaline, conc of OH- ions determines alkalinity
      • if we have a high concentration of hydroxide ions then we have a high ph, a very alkaline solution
      • low solubility - lower conc of OH- ions when dissolved, lower pH
    • using group 2 metals in neutralisation reactions farming
      • solid calcium hydroxide (lime) spread on fields - neutralises acids in the soil making it more favourable for crops
      • Ca(OH)2 (s) +Ca\left(OH\right)_{2\ }(s)\ +2H+ (aq)  Ca2+ (aq) +2H^{+\ }(aq)\ \rightarrow\ Ca^{2+\ }(aq)\ +2H2O(l)2H_2O(l) - water plus calcium salt
    • neutralisation reactions to treat indigestion
      • treating indigestion - often caused by excess hydrochloric acid in the stomach : can treat this in two ways
      • Mg(OH)2 (s) +Mg\left(OH\right)_{2\ }(s)\ + 2HCl (aq)  MgCl2 (aq) +\ 2HCl\ (aq)\ \rightarrow\ MgCl_{2\ }(aq)\ +2H2O (l)2H_2O\ (l)
      • uses milk of magnesia - suspension of Mg(OH)2 in water neutralises HCl to product magnesium chloride and water
      • could also use calcium carbonate
      • CaCO3(s) +CaCO_3(s)\ + 2HCl (aq)  CaCl2 (aq) +\ 2HCl\ (aq)\ \rightarrow\ CaCl_{2\ }(aq)\ +CO2 (g)+CO_2\ (g)+ 2H2O (l) \ 2H_2O\ (l)\
      • can't use calcium hydroxide, as alkalinity would be harmful to body tissue e.g. tissue lining throat
    • solubility of group 2 sulfates (e.g. MgSO4)
      • the solubility of group 2 sulfates decreases as we move down the group
      • magnesium sulfate highly soluble in water, whereas barium sulfate is insoluble
    • how can we use barium sulfate to treat patients? -a suspension of barium sulfate is given to patients before they have an X-ray of their digestive system - 'barium meal' -barium strongly absorbs x-rays allowing doctors to visualise the patient's digestive system - because barium sulfate is insoluble, it does not enter the patient's bloodstream
    • how can we use barium chloride to test for sulfate ions?
      • soluble in water, so solution of barium chloride contains aqueous barium ions
      • if we mix barium chloride solution, with a solution containing sulfate ions then the barium ions and sulfate ions form insoluble barium sulfate
      • this insoluble barium sulfate forms a white precipitate
      • however, we have to add either hydrochloric acid or nitric acid to our barium chloride solution before we test for sulfate because if there are any carbonate ions present then they will react with the barium ions
    • why do we add hcl/nitric acid before testing for sulfate ions?
      • to test for carbonate ions
      • if carbonate ions present, they would form barium carbonate which is insoluble so would form a white precipitate and give us a false positive test
      • hydrochloric acid or nitric acid reacts with carbonate ions, forming carbon dioxide
      • prevents us from getting a false positive
    • why is insolubility of barium sulfate useful?
      • useful in medicine - although barium sulfate can be toxic if it enters the bloodstream, because its insoluble it cannot be absorbed in the blood
    • flue gas removal
      • calcium oxide reacts with sulfur dioxide to remove it from factory pollutants and prevent it from released in to the atmosphere
      • it forms calcium sulfite and water
      • calcium oxide + water + sulfur dioxide -> calcium sulfite + water
    • magnesium in metal extraction
      titanium chloride + magnesium -> magnesium chloride + titanium
      • displacement reaction
    • magnesium react with steam
      • reacts faster as has extra energy
      • produces magnesium oxide + hydrogen
      • burns with a bright white flame and forms white powder (magnesium oxide)
    • melting point
      • decrease down the group
      • metallic meaning larger the ions within the metallic structure, weaker the attractive forces as the attractive force has to act over a much greater distance
      • melting points decrease down the group