Module 3 Flashcards
What is ionisation energy?
Measures how easily an atom loses electrons to form positive ions.
What is the first ionisation energy?
Energy required to remove one electron from each atom in one mole of gaseous atom of an element to form one mole of gaseous 1+ ions.
Factors affecting ionisation energy
Atomic radius
Nuclear charge
Electron shielding
Why does beryllium have a higher ionisation energy than boron
Boron marks the start of filling in the 2P sub shell and therefore it is easier remove the one electron than to remove one of the electrons of the 2s sub shell in beryllium.
Why does nitrogen have a higher ionisation energy than oxygen?
One of oxygens 2P orbitals is paired unlike nitrogen and therefore the two electrons repel each other making it easier to remove an electron from oxygen than nitrogen.
What is a giant covalent bond?
Where many billions of atoms are held together by only covalent bonds to form a giant covalent bond.
They’re usually- boron, carbon, silicon.
Group 2 reactivity trends
Becomes more reactive as you go down, this is because:
More electrons
Increase in atomic radius
Lower ionisation energies
Shielding increases
How do halogens exist in RTP?
As diatomic molecules
What is the trend of boiling point in Halogens
Boiling point increases.
As:
More electrons
Stronger london forces
More energy required to break the intermolecular forces.
Halogen-Halide displacement reactions (testing)
In water: pale green = Cl, orange = Br, Brown = I
Cyclohexane: pale green = Cl, orange = Br, Violet = I
Explain the displacement reactions of halogens.
Cl can displace both Br ions and Iodine ions.
Br only displaces iodine ions.
Therefore halogens are less reactive as you go down.
Explain the trend in reactivity of Halogens.
As you go down the group reactivity decreases. As halogens need to gain an electron which is hard as you go down.
This is because:
- atomic radius increases
- more inner shells so shielding increases
- so less nuclear attraction to capture an electron from another species
What is disproportionation reactions?
A redox reaction in which the same element is both oxidised and reduced.
Give an example of a disproportionation reaction?
Chlorine with water:
Cl2 (aq) + H2O — HClO (aq) + HCl (aq)
These products can be used to kill bacteria rather than just using harmful pure chlorine.
Reaction of chlorine with dilute, cold aqueous sodium hydroxide.
Cl2 (aq) + 2NaOH (aq) — NaCl + H2O + NaClO
Also a disproportionation reaction.
What are the benefits of Chlorine?
Ensures water is fit to drink.
Used for bleach.
Can kill bacteria.
What are the risks of Chlorine?
Extremely toxic gas
Respiratory irritant and can be fatal in a large quantity.
Chlorine in drinking water could react with organic hydrocarbons like methane.
But the risks of not adding the minimum amount of chlorine to water is far more lethal than risks posed by the hydrocarbons.
What is the test for halide ions?
Precipitation reactions with aqueous silver ions.
AgCl = White, AgBr = Cream, AgI = Yellow.
Qualitative analysis for ions.
- Carbonate test- Add dilute nitric acid, if you see bubbles, there is carbonates present. To further prove the gas is CO2 you can bubble it through lime water.
- Sulphate test- Add barium ions, if a white precipitate forms, it must contain a sulphate.
- Halide test- Add silver ions to identify the halide through the precipitate. Because the colours are so similar to further test it, add dilute aq ammonia if the precipitate dissolves it Cl, if it only dissolves in conc aq ammonia then it Br, if it doesn’t dissolve at all then it is iodine.
Why is there a specific sequence for qualitative testing?
Carbonate ions must be first as neither halide or sulfates bubble in a dilute acid.
Sulphate must be after carbonate as Barium carbonates can also form a white precipitate making it harder to identify the ions, so make sure there is no carbonates before using this test.
Halide test must go last as Ag ions with carbonates and Sulphates can also both form precipitates, so its important to eliminate any possibilities of any other ions being present.
How do you test if its one solution with a mixture of ions?
First do the carbonate test, but make sure that you continue to add dilute nitric acid until all the bubbling stops to ensure that all the carbonates have been removed.
Then when you’re doing the sulfate test make sure you use Barium nitrate and not barium chloride as that means chlorine ions will inevitably show up in the halide test. Make sure you add an excess of barium nitrate and to filter out all the barium nitrate.
Then lastly add AgNO3 [nitrate], therefore any precipitation here should just be halide ions. Then add dilute ammonia and if needed conc ammonia [aq].
What is the test for cations/ ammonia gas?
When heated, aq ammonium ions and aq hydroxide ions react to form together and for ammonia gas NH3.
Therefore add aq NaOH to the solution of ammonium ion. Ammonia gas will be produced and released by warming the solution.
Use a moist pH indicator paper and the paper should turn blue.
What is the difference between endothermic and exothermic?
Exothermic transfers energy (heat) from the system out to the surroundings.
Endothermic transfers energy from the surrounding to the system.
What is activation energy?
Minimum energy required for a reaction to take place.
