Chapter 8 Flashcards
(41 cards)
Elements in group 2
Alkaline earth metals that are reactive and do not occur in elemental form naturally - stable compounds like CaCO3
Why are the group 2 eleemnts reducing agents?
2 electrons in outer s sub shell that are lost to fomr 2+ ion - they act as reducing agents because the 2 electrons produced can be gained by smother species to reducd them. Eventually end up with electron config as a noble gas with each metal atom being oxidised
Grouo 2 reaction with oxygen
Forms metal oxide n; magneisum burns with a brilliant white light. Metal is oxidised - total changed balance out to net 0 ; totsl reduction and oxidation = 0.
Redox reactions with water
React with water to form sn slkaline hydroxide and hydrogen gas - reactivity increases down the group ghus reacfions get more and more vigorous
Redox reactions with dilute acids
Metal + acid - > salt + hydrogen ; reactivity increases down the group
Why does reactivity increase down group 2?
Requires first two ionisation energies ; both of which decrease going down the group because attrcation between nucleus and outer elecgrons decfeases as a result of increasing atomic radius and increasing shielding
Group 2 oxides + water
Releasing hydroxide ions and forming an alkaline solution of metal hydroxide
CaO + H2O -> Ca2+ (aq) + 2OH- (aq)
Griuo 2 hydroxides are only slightly soluble in watsr and when solution is saturated any further metal and hydroxide ions will form a solid precipitate
Ca2+ (aq) + 2OH- (aq) -> Ca(OH)2 (s)
Solubility of group 2 hydroxides
Increases down the group so the resulting solutions contain more OH- ions and are more alkaline; Mg(OH)2 us on,y slightly so,uble thus low alkaline Ph (10)
Ba(OH)2 is mcuh more soluble with greater OH- ion concentration and thus ph higher (13)
Group 2 compounds in agriculture
Calcium hydroxide is added to fields as lime by farmers to increase the pH of acidic soils - calcium hydroxide neytralised acid in the soil forming neutral water
Ca(OH)2 + 2H+ -> Ca2+ (aq) + 2H2O (l)
Grouo 2 compounds in medicine
Used as antacids for treating acid indigestion sith mang indigestion tablegs containg magnesium and calcium carbonates as main ingredients - milk of magnesia is a suspension of white magnesium hydroxide Mg(OH)2 in water ; acid in stomach is mainly HCl and thus neutralksation reaction takes place
Halogens
Do not appear in elementsl form - as negatively charged ions dissolved in sea water for example
Trends in boiling points
Increases down the group as there are more electrons thus stringer london forces so more energy required to break these intermolechlsr forces so boiling point increases
Fluorine
Pale yellow gas
Chlorine
Pale green gas
Bromine
Red brown liquid
Iodine
Shiny grey black solid
Astatine
Never been seen radioactive - decays rapidly
Redox reactions with halogens
5 electrons in outer p subshell - each halogen atom is reduced gaining an electron to form 1- ion
Cl2 + 2e- -> 2Cl-
Hallgens are the oxidising agent as another species js oxidised as a result of the hallgens losing electrons
Hallgen halide displacement reactions
Reactivity of hallgens decreases down the group - solution of each halogen added to halides ; if more reacfive than halogen displaces halide and solution changes colour to the halogen that is left
Solutions if halogens in water
Chlorine = pale green Bromine = orange Iodine = brown
Why is cyclohexane added?
Non-polar solvent with non polar hallgens disslving mlre readily - easjer to tell apart anf clntrast
Cl2 = pale green
Bromine = orange
Iodine = purp,e
Ionic equation of halogen halid reactions?
ALL AQUEOUS SOLUTIONS
Redox in halogen halide reactions
Halogen js reduced
Halide ion is oxidised
Fluorine and astatine?
Fluorine is too reactive with any substance
Astatine very rare and decays rapidly
