s-block - group 1

Question 1

what are group 1 metals called?

Answer 1

alkali metals

Question 2

what kind of compounds do s-block elements tend to form?

Answer 2

ionic compounds, as they are the most electropositive elements

Question 3

what electronic behaviour do we expect from group 1?

Answer 3

we expect group 1 elements to lose electrons, giving them a noble gas configuration, however they can also gain 1 electron to gian a full s orbital

Question 4

what kinds of metals are group 1 metals?

Answer 4

soft metals

Question 5

why are group 1 metals hard to store?

Answer 5

group 1 metals are reactive to air and moisture, meaning they must be stored in oil

Question 6

how does m.p/b.p change down group 1?

Answer 6

m.p/b.p decreases down the group - this shows that metallic bonding is what governs this property rather than dispersion forces

Question 7

summarise the metallic bonding model

Answer 7

metal cations in a cloud/sea of delocalised electrons, the strength of this interaction depends on the size of the cation, which increases down the group

Question 8

why do Li, Na and K float when reacting with water?

Answer 8

they have low densities, <1 - this is abnormal for metals

Question 9

what is a common identification method for group 1 metals?

Answer 9

they all have characteristic flame test colours

Question 10

give the characteristic flame test colours for group 1 metals - Li, Na, K, Rb, Cs

Answer 10

Li = red
Na = yellow
K = lilac
Rb = purple
Cs = blue

Question 11

how are group 1 metals produced?

Answer 11

Li and Na are produce by electrolysis of their molten chloride salts
K, Rb, Cs are produced by the reduction of their molten salts with Na at high temperatures

Question 12

how are group 1 oxides formed?

Answer 12

through combustion of alkali metals in air - the main product depends on the metal

Question 13

how do Li, Na and K react differently in air?

Answer 13

they form different oxide products
4Li + O2 -> 2LiO (oxide, O^2-)
2Na + O2 -> Na2O2 (peroxide, O2^2-)
K + O2 -> KO2 (superoxide, O2^-)
- Rb and Cs react similarly to K

Question 14

why does type of oxide formed by combustion of the metal in air change down group 1?

Answer 14

generally, large anions are stabilised better by large cations, and ionic radius of group 1 increases down group, so larger cations are better at stabilising the larger peroxide/superoxide ions with respect to decomposition into oxide - this is evidenced through lattice enthalpies, calculated via kapustinskii equation
- for ΔG = ΔH - TΔS, ΔS is dependent on identity of the metal, as stoichiometry of group 1 reactions are similar, if ΔS is constant the trend in ΔG will depend on differences in ΔH hence the trend in ΔH approximates reactivity of group 1, as long as ΔH is quite large

Question 15

how do group 1 oxides react with water?

Answer 15

group 1 oxides are basic + react with water to form hydroxides MOH
Na2O2 dissolution also gives H2O2
KO2 dissolution also gives O2 = disproportionation

Question 16

what is the chloroalkali process?

Answer 16

the electrolysis of NaCl(aq) in industry
2NaCl + 2H2O –> 2NaOH + H2 + Cl2
anode and cathode are separated by membranes of mercury metal, some of which will be left to the environment usually, this is bad

Question 17

where are alkali metal halides found?

Answer 17

abundant in nature + dissolved in oceans, especially NaCl

Question 18

how are group 1 halides made?

Answer 18

synthesized from hydroxides of carbonates with hydrochloric acid:
LiCO3 + 2HBr –> 2LiBr + H2O + CO2

Question 19

what structures are group 1 halides?

Answer 19

they form ionic crystal lattices

Question 20

carbide definition

Answer 20

binary compound of alkali metal + carbon, these are based on the dianion of acetylene (HC≡CH)

Question 21

nitride definition

Answer 21

triply protonated ammonia salts - Li is one of 2 elements that burns in nitrogen to form this, charge dense N ion likes to be with small Li cation

Question 22

give one common salt type of group 1 metals, other than halide salts

Answer 22

oxoanion salts, e.g. with CO3^2- or NO3^-

Question 23

can group 1 elements form coordination compounds?

Answer 23

yes, although group 1 cations are singly charged and quite large, so binding of ligands is weaker than for other cations, making ligands highly labil (fast exchange)

Question 24

crown ether definition

Answer 24

a macrocyclic polyether, containing 5 or 6 atoms/ether functional groups - these can act as ligands through O in ether functional groups, they bind strongly to group 1 metals and can be selective for metal ion size
- this selectivity can be used to isolate particular metals

Question 25

cryptands definition

Answer 25

ligands formed from the addition of an amine donor atom onto a crown ether, these allow bicyclic encapsulation giving more stable complexes - these allow the synthesis of alkides M- crypt + 2Na --> [(crypt)Na]+ where [(crypt)Na]+ is a sodide analogue of hydride

Question 26

what is the purpose of sodide anions?

Answer 26

they are very reductive species, capable of delivering/donating 2 electrons

Question 27

what is formed when alkali metals dissolve in liquid ammonia?

Answer 27

this dissolution produces solvated M+ cations and free electrons, the ammonia is a good ligand to stabilise the Na+ allowing electrons to be lost and stabilised by binding to the ammonia = free electride - the solution turns blue as a result - this electride is a very strong reductant

Question 28

can group 1 metals react with group 18 elements?

Answer 28

yes, at very high pressures all can react with Na e.g. Na2He, essentially = 2Na+ + 2electride + He there is little bonding between Na and He, however the He stabilises Na specifically in this complex, Na is the exact right size, other alkali metal complexes of He are less stable

Question 29

give 3 differences in the behaviour of H and the rest of group 1 elements + why they aren't so different after all

Answer 29

H is a diatomic nonmetal, the rest are metals - however when evaporated alkali metals can form dimer gases and at very high pressures metallic forms of H are possible H in its +1 O.S is very covalent, whereas +1 O.S of alkali metals forms ionic M+ salts - however Li+ often has covalent character, the naked Li+ cation is similarly unstable, slightly less H in -1 O.S. exists as hydrides, alkali metals don't - M- alkalides can be formed with crown ligands