Module 3 - [ch8] (reactivity trends)
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what are the group 2 elements also known as
alkaline earth metals
what is the most common reaction of group2 elements
redox loses its two outermost electrons and be reduced acts as a reducing agent
group2 metal + oxygen
metal oxide
group2 metal + water
alkaline hydroxide + hydrogen M(OH)2 + H2
how does reactivity of the group2 metals change going down the group
becomes more vigorous down the group reactivity increases down the group
metal + acid
salt + hydrogen
why does reactivity increase down group 2
the atoms of group2 lose 2 electrons to form 2+ ions ionisation energy decreases down the group due to increases atomic radius, electron shielding less energy needed for reaction to occur down the group
group2 oxide + water
release hydroxide ions (OH~) only slightly soluble in water when solution becomes saturated Ca+(aq) + OH~(aq) -> Ca(OH)2(s) solid precipitate formed
solubility of hydroxides in water
increases down the group down group contain more OH~ (aq) ions and are more alkaline, pH increases
what are group 2 compounds often used as
bases oxides hydroxides carbonates
group2 compound uses
Ca(OH)2 calcium hydroxide agriculture - added to fields as lime to increase pH of acidic soils neutralises acidic soil forming neutral water Mg(OH)2 magnesium hydroxide antacids to treat acid indigestion CaCO3 calcium carbonate + HCl (stomach acid)
equation for antacid
CaCO3(s) + HCl(aq) -> CaCl(aq) + H2O(l) + C2O(g) OR Mg(OH)2(s) + 2HCl(aq) -> MgCl2(aq) + 2H2O(l)
trend in boiling points of halogens
increases down group more electrons stronger london forces more energy required to break intermolecular forces
how do halogens exist
as diatomic molecules
most common type of reaction for halogens and why
redox each halogen atom has 7 electrons on outer shell only needs to gain one for stable noble gas configuration each halogen atom reduced to form 1- halide ion acts as an oxidising agent
what experiment can be carried to show how the reactivity of halogens decrease down a group
displacement reaction oxidation if the halogen is more reactive it displaces the halide in solution colour change Cl2(aq) Br2(aq) I2(aq) Cl~ X none none Br~ orange X none I~ purple purple X
how can you tell apart Cl2, Br2 and I2
solution in water Cl2 - pale green Br2 - orange I2 - brown not very clear, hard to distinguish between orange and brown + organic non-polar solvent cyclohexane shake non-polar halogens dissolve more readily in non-polar solvent Cl2 - pale green Br2 - orange I2 - violet
fluorine
pale yellow gas extremely reactive
astatine
extremely rare radioactive and decays rapidly never been seen predicted to be the least reactive halogen
reactivity of halogens
reactivity decreases down group atomic radius increases shielding increases nuclear attraction decreases more difficult to attract electron to outer shell
what is disproportionation
redox reaction in which the same element is oxidised and reduced
what is chlorine used in
water purification chloric acid produced (HClO) kills bacteria chloric acid(I) acid also acts as weak bleach
what type of reaction is chlorine and water give the equation
disproportionation Cl2(aq) + H2O(l) -> HClO(aq) + HCl(aq)
household beach what is the equation
NaClO Cl2(aq) + 2NaOH(aq) -> NaClO(aq) + NaCl(aq) H2O(l) disproportionation reaction between chlorine and water is limited by low solubility of chlorine in water if water has sodium hydroxide much more chlorine dissolves