Group 1 chemistry

Question 1

what is the alternative name for group 1?

Answer 1

alkali metals

Question 2

what is the general electronic configuartion for group 1?

Answer 2

[X]ns^1

Question 3

is group 1 hard or soft?

Answer 3

soft (can be cut with a knife)

Question 4

what are the melting points of group 1? why?

Answer 4

• Low melting points that decrease down the group
• weak metallic bonds due to few delocalised electrons and +1 ion charge

Question 5

what 2 things do group 1 react spontaneously with?

Answer 5

air and water

Question 6

reactivity down group 1 …

Answer 6

increases

Question 7

due to the high reactivity what form are group 1 elements usually found in?

Answer 7

as ions in solution (e.g. sea water) or as ionic solids (e.g. rock salt deposits)

Question 8

how do you extract group 1 elements?

Answer 8

To obtain elemental M, need to reduce the metal ions that occur naturally as M+ in solution or in MX solid salts.

Usually done by electrolysis of molten salts or solutions:
Electrolysis uses electric current to drive an otherwise non-spontaneous reaction

Question 9

are the ionisation energies of group 1 high or low? why?

Answer 9

• low (not very endothermic)
• Single valence electron is relatively easily lost, so chemistry of group 1 is dominated by M+ cations.

Question 10

what is required for a reaction to happen?

Answer 10

activation energy < reactants energy

Question 11

for alkali metals the sum of what 2 things can be considered the activation energy?

Answer 11

sum of the ionisation and atomisation enthalpies

Question 12

define enthalpy of atomisation

Answer 12

the enthalpy change when 1mole of gaseous atoms is formed from its element under standard conditions

Question 13

the enthalpy of atomisation is always _____ and _____

Answer 13

endothermic and positive

Question 14

what is the reactivity trend of group 1? why?

Answer 14

• Larger members (down the group) are even more reactive, thus having lower activation energies.
• General trend: ionisation energy and enthalpy of atomisation decrease down the group due to increased shielding and larger atomic sizes down the group.

Question 15

what are the anomalies of group 1 reactivity?

Answer 15

Anomalies seen at Rb & Cs are due to filling of 3d (and 4d) orbitals which are poorly shielding compared to s and p orbitals as they are less penetrating.

Question 16

what is lattice enthalpy?

Answer 16

a measure of the strength of the forces between the ions in an ionic solid.

Question 17

how does lithium react with water?

Answer 17

• Floats.
• Hydrogen bubbles given off but generally not hot enough to ignite

Question 18

how does sodium react with water?

Answer 18

• Floats.
• Sodium melts, large pieces can ignite the hydrogen, giving a characteristic yellow flame

Question 19

how does potassium react with water?

Answer 19

• Floats.
• Rapid reaction with auto-ignition of hydrogen. Purple flame and can explode.

Question 20

how does rubidium react with water?

Answer 20

• Sinks.
• Rapid reaction, with purple flame.
• Can explode.

Question 21

how does caesium react with water?

Answer 21

• Sinks.
• However, reaction is extremely rapid – explodes on contact.

Question 22

how are group 1 metals stored? why?

Answer 22

All group 1 metals react spontaneously with air, and so are usually kept under mineral oil or in sealed ampoules under a dry and inert atmosphere (or vacuum).

Question 23

what metal oxides do Li & Na form?

Answer 23

M2O (monoxide)

Question 24

what metal oxides do Na & K form?

Answer 24

M2O2 (peroxide)

Question 25

what metal oxides do Rb & Cs form?

Answer 25

MO2 (superoxides)

Question 26

why does lithium exclusively form monoxides?

Answer 26

High charge to size ratio (due to small size) makes Li too polarising. This distorts the O-O bond in either case (peroxide/superoxide), causing its breakage

Question 27

which is the only group 1 that forms a stable nitride?

Answer 27

Lithium (Li3N)

Question 28

why does lithium form a stable nitrate?

Answer 28

• Stability arises from the high lattice enthalpy (very exothermic).
• Li+ and N3- are small and have high charge-to-size ratios.
• Lattice enthalpy can be related to the size of the ions using the Kapustinskii equation
• Ultimately, this argument can be used to explain the trend in stabilities of the different alkali metal oxides.

Question 29

which ionic compounds show higher levels of covalency?

Answer 29

Small cations with a high charge-to-size ratio like Li+ are sufficiently polarising

Question 30

define hydration enthalpy of ions

Answer 30

the energy released when one mole of gaseous ions undergo hydration (dissolution in water).

Question 31

explain ions in aqueous solutions (3 points)

Answer 31

• Water is a polar molecule – the positive metal ion attracts the partially-negatively-charged oxygen atom in the water molecule.
• Results in the “coordination sphere” or “first solvation shell” of molecules surrounding the ion.
• The influence of the metal ion extends beyond the first solvation sphere.

Question 32

what interations create the second coordination sphere?

Answer 32

Interactions are ion-dipole or dative covalent (coordinate bonding) in nature in first sphere but extend beyond

Question 33

which group 1 ions are more polarising?

Answer 33

Smaller ions have a higher charge-to-size ratio, and so are more polarising

Question 34

how does the polarisation of an ion impact its hydrated ion?

Answer 34

The more polarising the cation, the more “layers” of solvent are attracted, meaning that the effective hydrated radii decrease down the group even though gas-state radii increase.

Question 35

how can you tell if the solubility of group 1 salts in water is favourable or not?

Answer 35

hydration enthalpy and lattice dissociation enthalpy

Question 36

why 3 things are in the hess’s cycle for solubility of group 1 salts?

Answer 36

• Lattice dissociation
• Enthalpy of hydration
• Enthalpy of solution

(ΔHsol = ΔHL(diss) + ΔHhyd)

Question 37

define lattice dissociation enthalpy

Answer 37

Energy required (endothermic) to convert 1 mole of an ionic solid to its constituent monatomic gaseous ions
(reverse of lattice enthalpy)

Question 38

define enthalpy of solution

Answer 38

enthalpy change when 1 mole of an ionic substance dissolves in water to give a solution of infinite dilution.

Question 39

why is it hard to predict the trends in solulbility of group 1?

Answer 39

Both hydration enthalpy & lattice enthalpy tend to decrease down the group (as ionic radius ↑).

Question 40

what is Gibbs free energy?

Answer 40

∆𝐺= ∆𝐻 −𝑇∆𝑆
(-∆𝐺 is favouble)

Question 41

what are complexes?

Answer 41

Metal ions have the propensity to form complexes with neutral/charged species containing lone pair electrons (ligands) via coordinate bonds

Question 42

what are 4 uses for metal complexes?

Answer 42

• Catalysis
• Analysis & diagnosis
• Pharmaceutical products
• Feature in biological processes and molecules (e.g. proteins)

Question 43

why is hydrogen not found in elemental form often?

Answer 43

due to its low density and high reactivity.

Question 44

why is hydrogen not associated with group 1?

Answer 44

• It varies greatly from the alkali metals as it forms cations (H+) more reluctantly than the alkali metals.
• Hydrogen has the propensity to form H- (hydride anions), just like halogens, to attain noble a gas configuration, although its electron affinity is less exothermic