Group 2 Flashcards
(20 cards)
Trend in ionisation energy?
- decreases down the group (1st and 2nd)
- more shells/atomic radius increases so - dis between nucleus & electron increases
- shielding increases - force of repulsion on electron increases
- nuclear charge increases BUT outweighed by 2 other factors
- less attraction between outer electron and nucleus
Reactions w O2?
- form metal oxides (bases) - white solids
- e.g. 2Mg(s) + O2(g) -> 2MgO(s)
- Ba most reactive - stored under oil to keep reacting w O2 & water vapour in air
React w Cl?
Mg(s) + Cl2(g) –> MgCl2(s)
Reactions w water?
general eq:
M (s) + 2H2O (l) –> M(OH)2 (aq) + H2 (g)
*calcium hydroxide - only slightly soluble in water so - liquid goes cloudy as precipitate of Ca(OH)2 forms
*Ba(OH)2 soluble in water so - aq
Mg + water?
*Mg reacts slowly w cold water - producing thin layer of Mg(OH)2 on Mg surface - slowing reaction even more
*BUT more vigorously w steam (g) - producing MgO & H2
Reactions of oxides with water?
group 2 oxides = basic oxides - can react w water to form alkalis
- observation: colourless solutions formed
- e.g. SrO (s) + H2O (l) –> Sr(OH)2
- simplified eq: O2- + H2O –> 2OH- (y it’s alkaline)
Trends in solubility of hydroxides?
- INCREASES DOWN THE GROUP
- pH of alkaline solution depends on: amount of oxides & H2O & Solubility of hydroxides - INCREASES down group
- e.g. Mg(OH)2 (s) formed very low solubility in water/BeO doesn’t dissolve at all
Testing for CO2?
- limewater goes cloudy as white precipitate forms
- limewater aka aq solution of Ca(OH)2
- CO2 + Ca(OH)2 –> CaCO3 + H2O
Milk of magnesia?
- used as indigestion remedy
- contains saturated solution of magnesium hydroxide mixed w extra solid magnesium hydroxide which acts as antacid(prevents/corrects acidity in stomach)
- HCl needed to digest food but too much - indigestion
- ts neutralises HCl:
Mg(OH)2 + 2HCl –> MgCl2 + 2H2O - very low solubility of Mg(OH)2 means conc. OH- very low so doesn’t affect health/attack human tissue
Reactions of oxides & hydroxides w acids?
- form salt & water
- neutralisation
- observations: white solid reacts to form colourless solution
- exothermic
lime in agriculture?
- use to control soil acidity so - greater yield of crops obtained
- lime - mostly Ca(OH)2…obtained from limestone (CaCo3)
- lime neutralises excess acidity in soil e.g…
Ca(OH)2 + 2HNO3 –> Ca(NO3)2 + 2H2O
Trends in solubility of sulfates?
- DECREASES DOWN GROUP
(*all group 2 nitrates & chlorides soluble) - Mg soluble
- Ca slightly soluble
- Sr & Ba insoluble
Testing for sulfate ions?
- presence of sulfate in solution shown by:
- add solution of Ba ions (e.g. BaCl2/Ba(NO3)2
- any sulfate ions in solution will react w Ba2+ ions to form white precipitate of BaSO4
- Ba2+ (aq) + SO4 2- (aq) –> BaSO4 (s)
-other anions could form white precipitate w Ba ions (especially carbonate ions) so - must be H+ ions to prevent BaCO3 forming as white precipitate so… - dilute HNO3/HCl
- barium meal b4 X-ray so - soft tissues show up more clearly due to dense white solid (meal contains insoluble BaSO4)
differences between Group 1 chlorides & Group 2 nitrates & carbonates and the result?
- charge on G2 cations double G1 cation
- size (ionic radius of G2 smaller G1 in same period
- nitrate & carbonate ions more complex than Cl- (change into smaller, more stable nitrite ion (NO2 -) or O2- by decomposing & releasing either gas) (CO3 2- changes into O2- ions by decomposing & releasing CO2)
Stabilities of nitrate & carbonate anions depend on…
- charge & size of cations
- smaller & more highly charged cations affect more
extra nitrates?
- all G1 & G2 nitrates are white solids
- if nitrate contains waters of crystallisation - steam also observed
- brown fumes indicates greater decomposition as (NO2) (for G2)
Group 2 carbonates?
–> metal oxides & CO2
CaCO3 –> CaO + CO2
*Li only G1 that decomposes at akk
Group 2 nitrates?
—> metal oxides + NO2 + O2
2Ca(NO3)2 –> 2CaO + 4NO2 + O2
*Li only G1 that does this
Nitrates & carbonates become more thermally stable down group (G2)?
- ions become larger so - 2+ charge spread out over larger area so - larger charge density
- larger charge density distorts electron cloud in anions more
- the less distortion - more stable
Group 1 nitrates?
–> nitrites + O2
- except Li
