trend for reactivity as reducing agents for group 2 elements and explain (ionisation energies)
reactivity as reducing agents increase down grpup 2,
as the number of electron shells increase, increasing shielding effect hence valence electrons are located in a shell with a higher principal quantum number
valence electrons are increasingly further away from the nucleus, less trongly attracted to nucleus despite increase in nuclear charge
smaller amount of energy to remove valence elctrons
sum of 1st and 2nd ionisation energies of group 2 elemets decrease down the group
increase ease of losing electrons to form cations, oxidation
reducing power and hence reactivity as reducing agents of group 2 elements increase down the group
what is the standard electrode potential
measure of tendency for species M^n+ to undergo reduction
trend for reactivity as reducing agents for group 2 elements and explain (standard electrode potential)
increasingly negative standard electrode potential value down group 2 for group 2 elements, greater tendency to be oxidised, increase in reducing power.
general equation for reaction of group 2 element with oxygen, and products, with state symbols, observation
2M(s) + O2(g) -> 2MO(s), all elements burn on heating with oxygen to give off light and heat
give all observations for group 2 elements react with oxygen (Be, Mg, Ca, Sr, Ba)
Be: forms a protective layer of BeO after heating in air which prevents further reaction
Mg: Burns with an intense brilliant white flame to form white solid MgO
Ca: Burns with brick-red flame to form white solid CaO
Sr: Burns with crimson flame to form white solid SrO
Ba: Burns with pale green flame to form white solid BaO
general trend of reactivity with oxygen down the group
increase
why do calcium strontium and barium need to be stored under mineral oil
they are very reactive to prevent reaction with oxygen in the air
What happens to Sr in finely divided or powdered form, and does it combine with inert gases like nitrogen when heated
catches fire spontaneously and burns vigourously, yes forms Sr3N2
observation for Be when reacted with water
no reaction with cold water/steam
general equation for group 2 elements with water
M(s) + 2H2O(l) -> M(OH)2 (s/aq) + H2(g)
observation for Mg when reacted with water and with steam
very slow reaction with cold water, but reacts more rapidly with steam.
why is Mg(OH)2 not formed with steam
Mg(OH)2 decomposes at high temperatures to MgO
equation for Mg reaction with both cold water and steam
slow:
Mg(s) + 2H2O(l) -> Mg(OH)2(s) + H2(g)
rapid:
Mg(s) + H2O(g) -> MgO(s) + H2(g)
observation for Ca, Sr, Br when reacted with water, and give equations
reacts vigourously
Ca(s) + 2H2O(l) -> Ca(OH)2(s) + H2(g)
Sr/Ba(s) + 2H2O(l) -> Sr/Ba(OH)2(aq) + H2(g)
trend for solubility of grp 2 metal hydroxides down the group
get more soluble down the group
trend in thermal stability of grp 2 carbonates and explain (explain how the grp 2 carbonates decompose and bring in decomposition temperature)
thermal stability, with decomposition temperature, increases down the group. the carbonates of group 2 elements decompose on heating to form stable oxides and carbon dioxide.
ionic radius of cation increases, charge density of cation decreases, polarising power of cation decreases, extent of polarisation of electron cloud of CO3^2- decreases, thermal stability and decomp tmperature increases
another factor affecting the ease of decomposition apart from charge density of cation, explain
size of anion, the larger the size of anion, the larger the electron cloud, easier to be distorted, more polarisable electron cloud.
give general equation of thermal decomposition of group 2 hydroxides
M(OH)2(s) -> MO(s) + H2O(g)
give general equation of thermal decomposition of group 2 nitrates, and colour of nitrogen dioxide gas
decompose on heating to give metal oxides, nitrogen dioxide and oxygen
2M(NO3)2(s) -> 2MO(s) + 4NO2(g) + O2(g)
brown nitrogen dioxide gas
