Group 1- Alkali Metals

Question 1

What is the outer electron configuration?

Answer 1

ns1

Question 2

What is the enthalpy of solvation?

Answer 2

This is the enthalpy change that accompanies the solvation of a gaseous ion.

M+(g) -> M+(aq)

Question 3

What is the enthalpy of atomisation?

Answer 3

The enthalpy change when one mole of gaseous atoms are formed an element in its standard state.

M(s) -> M(g)

Question 4

What is the trend in 1st ionisation energy down the group?

Answer 4

• Decreases down the group
  This is due to reduced shielding and more shells so less electrostatic attraction and so less energy is required

M(g) -> M+(g) + e-

Question 5

What is the trend in atomic radius down the group?

Answer 5

It increases due to more shells

Question 6

What is group 1 chemistry dependent on?

Answer 6

It is dependent on the M+ ion with a suitable anion

M+(aq) + e- -> M(s)

Question 7

Which element is an exception?

Answer 7

Lithium

Question 8

Why does lithium has a large hydration enthalpy?

Answer 8

Lithium has a large charge density as its is small
Oxygen in water is very attracted
This means there is a large release from bond formation

Question 9

Why do large atoms have a low hydration enthalpy?

Answer 9

Small charge density
Weaker attraction to water
Less energy is released from bond formation

Question 10

Why is lithium an exception?

Answer 10

It is very polarising due to its high charge density
This means it can distort electron clouds in other ions
- it pulls the electron density towards itself
This induces covalent character in the bonds

Question 11

Give examples of how lithium shows exception

Answer 11

• has the greatest 1st I.E ( overcome by large hydration enthalpy)
• best reducing agent
• react with N2 to give nitride
• Burns in air to give oxide LiO2 (others give peroxides)
• LiCO3 and LiOH decompose on heating (others are stable)
• LiNO3 decomposes on heating to give Li2O (others give nitrites MNO3)

Question 12

What is an organometallic?

Answer 12

A compound that has a bond between a metal and a carbon

Question 13

What is a Grignard reagent?

Answer 13

Compounds with the general formula RMgX

Question 14

What is a diagonal relationship?

Answer 14

When you move diagonally on the periodic table, effects cancel out

-Increasing orbital size (down) and zeff (across)
This leads to similar properties as they have similar radii

Question 15

What is the relationship between Li and Mg?

Answer 15

They are diagonally related and so have similar properties

Question 16

What are the similarities in chemistry of Li and Mg?

Answer 16

• both form stable nitrides (G1 are unstable)
• carbonates of Mg and Li decompose (G1 needs harder heating)
• form covalent organometallics (G1 form ionic)
• Mg and Li burn in air to form oxides (G1 form peroxides)
• more heavily hydrated

Question 17

What are Fajans rules?

Answer 17

• small highly charged cations have polarising ability
• large, highly charged anions are easily polarised
• large anions electrons have weak interaction with nucleus so easily distorted
• cations that don’t have noble gas configuration are easily polarised

Question 18

Describe polarising ability and polarisability based on radius

Answer 18

Small cations have large polarising power (large charge density)
Large cations have weak polarising power
Small anions have low polarisability (electrons are held close to nucleus)
Large anions have high polarisability

Question 19

Describe the bonding in lithium organometallics

Answer 19

Covalent character as lithium can distort electron density

Question 20

How must organometallics be prepared?

Answer 20

With a dried solvent ( as they react with water) and an inert atmosphere (N2) as they react with oxygen

Question 21

What sort of structures do heavier alkali metals tend towards?

Answer 21

Heavier, large metals are more ionic (low polarising ability) and so tend towards ionic structures

Question 22

Describe the reactivity and chemistry of lithium organometallics

Answer 22

Highly reactive (burn in air) and thermally unstable

• act as strong base
• initiators for polymerisation
• synthesis of main group alkyls

Question 23

Why are G1 weak acids and coordinate weakly?

Answer 23

Ions are singly charged and large and so have low charge densities

Coordination becomes weaker down the group as charge density decreases

Question 24

What happens when a group 1 metal dissolves in liquid ammonia?

Answer 24

They form a dark blue solution 
M -> Na+ +e-
NH3 solvates ions and electrons 
Reversible and NH3 can be removed where metal is unchanged
Conducts electricity (delocalised e-)

Question 25

What causes the colour change when metal is dissolves in ammonia?

Answer 25

The colour is independent of the metal and is due to the presence of solvated electrons
They sit in cavities formed by groups of Nh3 molecules

Question 26

What is sodium in liquid ammonia used for?

Answer 26

To reduce metal ions to low oxidation states

The solvated electrons act like free electrons so the solutions are strong reducing agents

Question 27

What colour are dilute solutions of alkali metal in NH3?

Answer 27

They are bright blue

Question 28

How can you quantitative tell the metal does not cause the colour (in ammonia)

Answer 28

The UV vis spectra of the solutions are the same even if the metal changes
This means the species giving the colour does not contain the metal

Question 29

Why do metals in ammonia conduct electricity?

Answer 29

Delocalised electrons

Measurement show they are paramagnetic