Group 1 and 2 Flashcards
reason for Li and Mg to have a diagonal rel
from Li to Na; polarizing power decreases so Li+ has greater pol power. this is due to smaller size of Li
between Na and Mg, Mg2+ Has a greater pol pwoer bc it has a higher chagre and roughly the same size.
Li and Mg form compounds with a similar degree of polarising power and covalent character.
explain the low 1st IE of group 1
group 1 elements are relatively large in size and the electron that needs to be removed is single and in an s orbital.
explain why the 1st IE of group 1 is much lower than the 2nd IE
in the 1st IE the lectron is removed from an s orbital while in the 2nd IE the elexctron is removed from a noble gas core which is closer to the nucleus and hence requires more energy.
what affects does the increase in size and increase in shielding on going down the group 1, have on group 1 elements
this allows the outermost electron to be lost with increasing ease. this results in increase in reactivity and electopositive character as the ram increases.
how are group 1 metals stored?
under oil
reason for group 1 metals to have colured flames
since the outermost electron is easily excited
flame test of Li
red
flame test of Na
bright yello
flame test of potassium
lilac
flame test of rubidium
red
flame test of caesium
blue
why does the melting point decrease on going down group 1
this is due to the large atomic size which leads to weaker forces between neighbouring atoms. thi sis because of the reduced attration of the nuclear charge for the shared mobile outer electrons as these e- get further away
characteristics of group 1 salts
usually white unless anoin is coloured,,, all soluble in water
structure of group 1 elements
body centered cubic structrue. cubic with an atom at the centre surrounded by 8 other atoms.
group 1 reaction with wtaer
h2 and hydroxide
reaction of group 1 elements withh O2; Li, Na, K, Rb and Cs
Li makes Li2O lithium monoixde
Na makes Na2O
in excess O2 Na produces Na2O2 (peroxide)
K, Rb and Cs react with O2 to produce superoxides of KO2, RbO2 and CsO2
what makes a salt stable?
they become more stable upon increase of an ionic chare or decrease in ionic radius. these will make it easier to approach each other in the solid crystal
examples to illustrate the diagonal relationship between Li and Mg
decomposition on heat of nitrates;
group 1; NaNO3 = NaNO2 and O2
Li and Mg: LiNO3 =Li2O + NO2 and O2
thermal stability of group 1 nitrates
+O2;;; grp1 form peroxides and super oxides
Mg and Li give the oxide
heating carbonates- grp 1 stable, Li and Mg give oxide and CO2
heating hydroxide- grp 1 stable, Li and Mg give oxide and water
heating nitrateV- grp 1 give nitrite and O2, Li and Mg give oxide, NO2 and O2
grp 1 hydrogencarbonates can exist as solids, Li and Mg only exist in soution
thermal stability of carbonates of group 1
thermally stable apart from Li which produces Li2O and CO2
thermal stability of hydrogen carbonates of group 1
only group to form stable, and SOLID hydrogen carbonate compounds. apart from Li.
on heat; NaHCO3 = Na2CO3 + CO2 and H2O
Li prodcues the same products but LiHCO3 is only stble in solution
stability fo hydroxides of group 1
stable apart from LiOH which produces Li2O and H2O
reactions of group 1 oxides and peroxides with water
Na2O + H2O = NaOH
Na2O2 +H2O = NaOH +H2O2
quality of group 1 hydroxies( excluding Li)
they are deliquescent- asorb water vapour from the air and issolve in it
characteristic of hydrated sodium carbonate
effflorescent -loses water of of crystalliation without heating
flame test of calcium
brick reed
flame test of strontium
crimson
flame test of barium
apple green
is mp and bp of group 2 higher than those of group 1?
yes, due to 2 electrins being avalible for metallic bonding.
solubility of group 1 compounds with refernce to hydration and lattice enthalpies
first there is the seperation of the ions. endothermic. the neergy supplied is equal to the lattice energy. the second step is hydration of the ions. exothermic. the energy released is the hydration energy.
all common salts are solubel since the cations ar esinglky charged and energy required to break the lattice is low
Is the first IE of group 2 higher than that of group 1?
yes, from group 1 to group 2, electrons are enterin gthe same shell so shielding remains the same. the nuclear charge and atomic radius are decreasing resulting in greater elecrostatic force of attraction between the nucleus on the outer electron.
reaction of group 2 metals with water
they liberate H2 and the hydroixde. Be does not react with water and Mg reacts with steam to make MgO and H2
reaction of group 2 with oxygen. mentions requiremnts for Mg and any specific info abt Ca
all react to form white solid monoxides. mg does not react with dry airat room temp, but pxides in damp air forming MgO which becomes teh hydroxide and then carbonate.
on exposure to air Ca forms CaO, then Ca(OH)2 with water and CaCO3 with CO2
what makes thermal stability? how does decomposing into different compounds help achieve stability?
the greater the charge and smaller the ion the more stable the compound as the ions will be able to approach closer to each other. large aninos decompose on heating to form smaller ions such as oxides,, the charge of 2- is spread over a smaller ion therefore the oxide would be more strongly attracted to the cation
group 2 nitrate thermal stability
decompose to from oxide, NO2 and O2
thermal stability of grou p2 carbonates
oxide and CO2
thermal stability of group 2 hydrogen carbonates
only exist in solutions bc they are very unstable
decompose to corm carbonates, H2O and CO2
thermal stability of grp 2 hydroxides
decompsoe to form oxide and water
discuss lattice enthalpy and hydration enthalpy difference for small and large ion in the compound
small ion; highly endothermic lattice dissocation (hard to break up) and highly exothermic hydration. vice versa for large ions
solubility of sulfates of grp 2
MgSO4 -soluble CaSO4- sparingly soluble SrSO4- insoluble BaSO4-insoluble down the grp; change in lattic disssocation is negligble due to large size of SO42-. cation size increases so decrease in enthalpy of hydration (difficult to attract water). on adding lattice diss and hydration ent, the value for enthalpy of solution becomes less exo therefore less soluble
solubility of grp 2 hydroxies
OH- is a small ion and lattic ent is very significant. due to increase in cation size down the grp, lattice enth decreases. the rate at which lattic end becomes less endo is more than the rate at which ent of hydration becomes less exo so on going down the grp, solubility increases
two ways of distinguishing between mg2+ and Ba2+
- add NaOH- Mg2+ forms a white ppt and Ba has no visible reaction
- add H2SO4- no visible reactino with Mg2+, white ppt with Ba2+
hardness of group 2 metals down the group
harndess decreases due to weakining of the metallic bond. the radisu is increasing therefore less attraction between the nuclei and delocalised electrons
comment on the ionic/covalent character of the chlorides of Na, Mg and Al and if they can be hydrolysed
NaCl is ionic, MgCl2 is partially covalent and AlCl3 is found as a simple molecular compound(high degree of covalent character).
NaCl ionizes, MgCl2 partially hydrolyses to form Mg(OH)Cl2 and AlCl3 undergoes complee hydrolysis
why is MgO more stable than MgCO3? why are group 1 carbonate sstable
across a period the size of the cation decreases but the charge increases therefore Mg2+ has a higher polarizing power than Na+. the increases in polarising power, the greater the distortion of the e- cloud of the anion, causing MgCO3 to decoposse to MgO and CO2.
O2_ is a small ion with a high charge and it is not easily polarisbale making MgO stable.
stability of carbonates down group 2
stability increases as the size of te cation increases causing less distortion of the e-cloud of the carbonate anion due to smaller polarising power.
how to make Mg(OH)2
react Mg with NaOH
