Groups one and two Flashcards
outer shell electrons in gr2
2
going down the groups, metals become more reactive reason
although the nuclear charge increases down the group, there is increased shielding and a larger distance between the outermost electron and nucleus which cause a weak attraction that outweighs having a high nuclear charge
reactivity increases down groups
easier for atoms to lose electrons
increasingly vigorous reactions caused
reactions of group 2 metals with oxygen
2M (s) + O2 (g) → 2MO (s)
Sr and Ba also form a peroxide (MO2)
reactions of all metals with water
M (s) + 2H2O (l) → M(OH)2 (s) + H2 (g)
Except for, Be which does not react with water
what type of solution do the reactions with water create
alkaline (presence of OH)
reactions with chlorine
Mg (s) + Cl2 (g) → MgCl2 (s)
what happens to the solutions formed with water when going down the group
becomes more alkaline
what is calcium hydroxide
limewater
reactions of group 2 oxides with sulfuric acid
insoluble sulphates form at the surface of the oxide so solid underneath cant react with acid.
oxide + dilute sulfuric acid → sulfate + water
reaction of group 2 hydroxide and HCl/SO4
colourless solutions of metal salts.
sulphates decrease in solubility down group
Hydroxides still increase
hydroxide + dilute hydrochloric acid → chloride + water
hydroxide + dilute sulfuric acid → sulfate + water
group 2 hydroxides trend in alkalinity
become more alkaline down the group
he higher the concentration of OH- ions formed, the more alkaline the solution
The alkalinity of the formed solution can therefore be explained by the solubility of the Group 2 hydroxides
GROUP 2 hydropxides solubility and alkalinity _____
down the group
INCREASES
GROUP 2 sulfates solubility _____
down the group
decreases
(alkalinity not affected as no OH)
thermal decomposition
the breakdown of a compound into two or more substances using heat
only group 1 carbonate that decomposes
lithium -
rest of the group 1 carbonates cant decompose at bunsen temps
carbonate decompose equation
XCO3 (s) rightwards arrow with HEAT on top XO (s) + CO2 (g)
only nitrate G1 that will decompose to form nitrogen dioxide
lithium nitrate LiNO3
4LiNO3 (s) rightwards arrow with HEAT on top 2Li2O (s) + 4NO2 (g) + O2 (g)
what happens in decomposition of group 1 nitrastes except lithium
dont decompose fully and produce metal nitrite and oxygen
2XNO3 (s) rightwards arrow with HEAT on top 2XNO2 (s) + O2 (g)
group 1 nitrate decomposition gets more difficult
higher temps needed
Since the formed nitrogen dioxide gas is toxic
store in fume cupboard
The general equation for the decomposition of Group 2 nitrates is:
X(NO3)2 rightwards arrow with HEAT on top XO + 1 halfO2 + 2NO2
thermal stability of group 1 and 2 nitrates and carbonates increases down the group
smaller ions at top of group are more polarising of the anions
smaller cation attracts delocalided electron in the carbonate towards itself
the higher the charge and smaller ion = more polarising
more polarised = more likely to thermally decompose as bonds in carbponate and nitrate are weaker
down group ions become larger
lower charge density
less distorting
less likely to thermally decompose
flame test method
Dip the loop of an unreactive metal wire such as nichrome or platinum in concentrated acid, and then hold it in the blue flame of a Bunsen burner until there is no colour change
This cleans the wire loop and avoids contamination
This is an important step as the test will only work if there is just one type of ion present
Two or more ions means the colours will mix, making identification erroneous
Dip the loop into the solid sample and place it in the edge of the blue Bunsen flame
Avoid letting the wire get so hot that it glows red otherwise this can be confused with a flame colour
