Periodicity/Groups 2 and 7 Flashcards
What is the definition of 1st ionisation energy?
The energy required to remove 1 electron from each atom in one mole of GASEOUS atoms to form one mole of GASEOUS 1+ ions
Write the equation for the 1st ionisation energy of Na
Na(g) –> Na+(g) + e-
Write the equation for the 2nd ionisation energy of Na
Na+(g) –> Na2+(g) + e-
What is ionisation energy proportional to?
The strength of the attraction between the nucleus and outer e- (nuclear attraction)
What does the strength of nuclear attraction depend on?
Radius
Shielding
Charge
How does atomic radius affect nuclear attraction?
As atomic radius increases, nuclear attraction weakens (outer e- further away from nucleus)
How does electron shielding affect nuclear attraction?
Shielding reduces attractive force from protons on outer e- (more inner shells = larger shielding effect)
How does nuclear charge affect nuclear attraction?
More protons in nucleus = greater attraction on outer e-
How does ionisation energy change down a group?
Radius increases (more shells) Shielding increases (more inner shells) Charge increases BUT is outweighed by R and S
Therefore nuclear attraction on outer e- DECREASES so outer e- is easier to remove - ionisation energy DECREASES
How does ionisation energy change across a period?
Radius decreases (increasing nuclear charge pulls in outer e-) Shielding remains constant (same no. inner shells) Charge increases (more protons)
Therefore nuclear attraction on outer e- INCREASES so outer e- is harder to remove - ionisation energy INCREASES
Why is the 1st ionisation energy of B less than Be?
B: 1s(2)2s(2)2p(1)
Be: 1s(2)2s(2)
The outer e- is in a 2p subshell in B and 2s in Be - 2p is higher in energy than 2s so outer e- in B is easier to remove
Why is the 1st ionisation energy of O less than N?
1s 2s 2p N: ⬆️⬇️ ⬆️⬇️ ⬆️⬆️⬆️
O: ⬆️⬇️ ⬆️⬇️ ⬆️⬇️⬆️⬆️
The outer e- in N is UNPAIRED whilst in O it is PAIRED - paired e- experience more repulsion than unpaired e- so the outer e- in O is easier to remove
What is the trend in reactivity down group 2?
Atomic radius decreases ionisation energy
Shielding decreases ionisation energy
Nuclear charge increases ionisation energy but is ignored as it is outweighed by R and S
Therefore easier for outer e- to be removed so reactivity INCREASES down group 2
What is the solubility trend in group 2 hydroxides?
Increases down the group
What does an increase in pH down group 2 hydroxides show?
More OH- ions released down the group
How are hydroxides used in agriculture?
Neutralise acidic soil
What are the colours of Cl2, Br2 and I2 (halogens) in water and cyclohexane (non-polar organic solvent)?
Water Cyclohexane
Cl2 Pale green Pale green
Br2 Orange Orange
I2 Brown Violet
What is a displacement reaction?
A reaction between a halogen and a halide ion
What colour are halides?
Colourless
What is the reactivity trend between Cl2, Br2 and I2?
Cl2 Br2 I2
——————————->
reactivity decreases
What are the displacement reactions?
Halogen/halide Chloride Bromide Iodide
A O A O A O
Chlorine X X orange brown violet Bromine X X X X brown violet Iodine X X X X X X
Which halides will chlorine, bromine and iodine displace?
- Chlorine will displace bromide and iodide ions
- Bromine will displace iodide ions
- Iodine won’t displace anything (least reactive)
Write the ionic equations for all the displacement reactions that CAN occur
Cl2 + 2Br- –> 2Cl- + Br2
Cl2 + 2I- –> 2Cl- + I2
Br2 + 2I- –> 2Br- + I2
What are the halide reactions?
NaCl + silver nitrate –> white precipitate
+ dilute ammonia –> dissolved
+ conc. ammonia –> dissolved
NaBr + silver nitrate –> cream precipitate
+ dilute ammonia –> remained cream ppt.
+ conc. ammonia –> dissolved
KI + silver nitrate –> yellow precipitate
+ dilute ammonia –> remained yellow ppt.
+ conc. ammonia –> ppt. yellow to white colour change
Why can chlorine behave as an oxidising agent?
Highly electronegative so can accept electrons to form a Cl- ion
Why is cyclohexane added to the test tubes when carrying out displacement reactions?
Colours are more distinct in organic solvents
What is required in order for a displacement reaction to happen?
The halogen needs to be more reactive than the halide present
Cl2 Br2 I2
——————————>
reactivity decreases
What is the reactivity trend down group 7?
Atomic radius increases (more shells) Shielding increases (more inner shells)
Therefore there is less nuclear attraction to GAIN (group 7 gain an e-) an e- so reactivity DECREASES and oxidising strength decreases
