Group 1- Alkali Metals Flashcards
What is the outer electron configuration?
ns1
What is the enthalpy of solvation?
This is the enthalpy change that accompanies the solvation of a gaseous ion.
M+(g) -> M+(aq)
What is the enthalpy of atomisation?
The enthalpy change when one mole of gaseous atoms are formed an element in its standard state.
M(s) -> M(g)
What is the trend in 1st ionisation energy down the group?
- 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-
What is the trend in atomic radius down the group?
It increases due to more shells
What is group 1 chemistry dependent on?
It is dependent on the M+ ion with a suitable anion
M+(aq) + e- -> M(s)
Which element is an exception?
Lithium
Why does lithium has a large hydration enthalpy?
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
Why do large atoms have a low hydration enthalpy?
Small charge density
Weaker attraction to water
Less energy is released from bond formation
Why is lithium an exception?
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
Give examples of how lithium shows exception
- 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)
What is an organometallic?
A compound that has a bond between a metal and a carbon
What is a Grignard reagent?
Compounds with the general formula RMgX
What is a diagonal relationship?
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
What is the relationship between Li and Mg?
They are diagonally related and so have similar properties
What are the similarities in chemistry of Li and Mg?
- 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
What are Fajans rules?
- 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
Describe polarising ability and polarisability based on radius
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
Describe the bonding in lithium organometallics
Covalent character as lithium can distort electron density
How must organometallics be prepared?
With a dried solvent ( as they react with water) and an inert atmosphere (N2) as they react with oxygen
What sort of structures do heavier alkali metals tend towards?
Heavier, large metals are more ionic (low polarising ability) and so tend towards ionic structures
Describe the reactivity and chemistry of lithium organometallics
Highly reactive (burn in air) and thermally unstable
- act as strong base
- initiators for polymerisation
- synthesis of main group alkyls
Why are G1 weak acids and coordinate weakly?
Ions are singly charged and large and so have low charge densities
Coordination becomes weaker down the group as charge density decreases
What happens when a group 1 metal dissolves in liquid ammonia?
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-)
What causes the colour change when metal is dissolves in ammonia?
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
What is sodium in liquid ammonia used for?
To reduce metal ions to low oxidation states
The solvated electrons act like free electrons so the solutions are strong reducing agents
What colour are dilute solutions of alkali metal in NH3?
They are bright blue
How can you quantitative tell the metal does not cause the colour (in ammonia)
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
Why do metals in ammonia conduct electricity?
Delocalised electrons
Measurement show they are paramagnetic
