Orbitals

Question 1

properties

Answer 1

alkaline earth metals

higher melting metals

less reactive in air than group 1 - only Ba stored under oil

Question 2

occurence

Answer 2

Mg (2.1%) + Ca (4.1%) = v. abundant + in earth’s crust

Mg2+ = 2nd most abundant metal in sea water

Question 3

preparation

Answer 3

[from sea water] - Mg2+ + Ca(OH)2 -> Ca2+ + Mg(OH)2

then conversion to MgCl2 with HCl

followed by electrolysis of molten MgCl2
Mg2+ + 2e- -> Mg
2Cl- -> Cl2 + 2e-

[from magnesite, MgCO3, or dolomite, MgCO3-.CaCO3)

1st conversion to oxides by heating - MgCO3.CaCO3 -> MgO.CaO + 2CO2

2nd heating with ferrosilicon to 1200°C - 2MgO.CaCO + Si -> Ca2SiO4 + 2Mg

Question 4

calcium

Answer 4

in many minerals - limestone (CaCO3) + apatite (Ca3(PO4)2)

metal produced by heating CaO with Al: 6CaO + 2Al -> 3CaO.Al2O3 + 3Ca

Question 5

beryllium

Answer 5

occurs in some minerals (beryl - 3BeO.Al2O3.SiO2)

little use due to toxicity

Question 6

strontium (0.03%) + barium (0.04%)

Answer 6

occur in minerals similar to Ca minerals

elements can be isolated by electrolysis or reaction with Al

Question 7

oxides

Answer 7

2M + O2 -> 2MO

BeO = rock salt structure (not ionic -> hexagonal wurtzite structure)

BaO reacts with excess air to produce peroxides - 2BaO + O2 -> 2BaO2 (600/700°C)

Question 8

hydroxides

Answer 8

MO + H2O -> M(OH)2

except Ba: Ba + H2O -> M(OH)2 + H2
Ba(OH)2 can be prepared by ppt - BeCl2 + 2OH- -> Be(OH)2 + 2Cl-

all hydroxides basic in water (except Be)

increased solubility down group

Be(OH)2 = amphoteric (reacts with acid + base)
Be(OH)2 + 2H3O+ -> Be2+ + 4H2O
Be(OH)2 + 2OH- -> [Be(OH)4]2- + 4H2O

Question 9

halides

Answer 9

M + X2 -> MX2

all alkaline earth metals react with halogens to give water soluble dihalides

all (except Be) have ionic lattice structure
Be has polymeric structure with covalent bonds

Question 10

carbonates

Answer 10

not v. soluble

ppt from basic solutions when CO2 added

M2+ + CO2 + 2OH- -> MCO3 + H2O

formation of CaCO3 from calcium-containing water = limescale

carbonates lost CO2 on heating

CaCO3 -> CaO + CO2

Question 11

decomposition temp. - carbonates vs oxides

Answer 11

lower for oxides that have high lattice enthalpies compared with their carbonate

ΔHk = large and positive (less strongly +ve if lattice enthalpy of oxide > carbonate)

Question 12

compounds with carbon

Answer 12

common binary compounds with carbon (carbides) are based on dianion of acetylene (HC≡CH)

CaO + 3C -> CaC2 + CO (= prep of calcium carbide)

CaC2 + H2O -> Ca(OH)2 + HC≡CH

Question 13

compounds with N and other oxoanions

Answer 13

Mg is 1 of 2 elements (Li = other) that burns in N2

3Mg + N≡N -> Mg3N2 (nitrides)

other group 2 salts of oxoanions also decompose on heating

MgSO4 -> MO + SO3 (smaller anion = driving force)

Insoluble BaSO4 used in x-ray contrast agent (never releases toxic Ba2+)

Question 14

coordination chemistry

Answer 14

increases down group

larger cation = higher coordination number

Question 15

what causes diagonal relationships between elements?

Answer 15

radius:charge ratio

[down group]
-increasing atomic radius
-increasing ionic radius
-decreasing ionisation enthalpy

[across period]
-decreasing atomic radius
-decreasing ionic radius
-increasing ionisation enthalpy

[diagonally]
-vertical and horizontal trends largely cancel out

Question 16

what are organometallic compounds?

Answer 16

compounds of metals with bonds to carbon

Question 17

properties of organometallic compounds

Answer 17

highly air + moisture sensitive

MeLi + nBuLi = most common

Mg reacts with RX [Grignard reagents] - RX + Mg -> RMgX

Question 18

homoleptic

Answer 18

one type of ligand

Question 19

Schlenk equilibrium

Answer 19

2RMgX -> MgR2 + MgX2