Inorganic AS AQA Chemistry

Period 3 atomic radius

Decreases - Nuclear charge increases, and the additional electron is in the same principle energy level, meaning it is the same distance away from the nucleus. Therefore, the attraction of the nucleus on the outer electrons increases, and they are pulled in closer to the nucleus

Covalent radius

1/2 the distance between the 2 nuclei

Shielding

an effect where some of the positive attraction of the nucleus is cancelled due to repulsion from electrons in lower energy levels

Periodicity

the repeating pattern of certain properties of elements across a period

Period 3 first ionisation energy - general

Increase - nuclear charge increases, and the additional electron is in the same principle energy level, meaning it is the same distance away from the nucleus. Therefore, the attraction of the nucleus on the outer electrons increases, and more energy is required to remove it (shielding is similar, and atomic radius is lower)

Period 3 first ionisation energy - exceptions 1

Mg to Al decrease - electron removed from Al is in the 3p sub energy level, which is slightly further away from the nucleus and receives more shielding than the electron removed from Mg which is in the 3s orbital

Period 3 first ionisation energy - exceptions 2

P to S decrease - electron removed from S is in an electron pair (in P it is not). The repulsion between the 2 electrons lowers the effective nuclear charge on the electron, meaning less energy is required to remove it.

Period 3 melting points - explanation of trend: Na, Mg, Al

Increase - higher charge on metal ion ( and therefore more delocalised electrons) means stronger electrostatic attractions between electrons and ions, which requires more energy to break

Period 3 melting points - explanation of trend: Al, Si, P

Inverted V - Si has a macromolecular structure, with each Si atom covalently bonded to 4 other. Covalent bonds are very strong and require a lot of energy to break, more energy than vdw between molecules of P4 and more than metallic bond in Al

Period 3 melting points - explanation of trend: P, S

Increase - S exists as molecules of S8, where as P exists as P4. S8 is has a higher Mr so more vdw form between molecules

Period 3 melting points - explanation of trend: Cl, Ar

Decrease - Cl exists as diatomic molecules, Ar exists as single atoms, more vdw form between Cl2 molecules

Group 2 first ionisation energy

Decrease - atomic radius increases, so electron is less attracted to nucleus and less enrgy is needed to remove it

Group 2 atomic radius

Increase - number of full energy levels increases

Group 2 melting point

Decrease - as the ionic radius of ion increases, delocalised electron further away from positive attraction of the nucleus - and so is less strongly attracted

What 3 things does the strength of the metallic bond depend on?

1) Ion radii 2) Ion charge 3) Ion packaging

Reaction of Mg in warm liquid water

Mg + 2H20 → Mg(OH)2 (s) + H2

Magnesium Hydroxide is a sparing soluble, so rxn will stop once Mg is coated by a layer of it

Reaction of Mg in steam

Mg + H20 (g)→ MgO + H2

Observation of Mg in steam

White flame, faster than rxn with liquid water

Reaction of Ca, Sr and BA with cold water- what is produced and what happens to the solution? Is there something different with Ca?

Production of hydroxides

Solution will heat up (increase down group)

Solution will be alkali

For Ca- some white precipitate will form as only slightly soluble

Group 2 - trend in reactivity

Increase - Atomic radius increases so can more easily give up 2 electrons, as further away from positive attraction of the nucleus (ionisation energies)

Group 2 - solubility of hydroxides

Increase (Mg(OH)2 is sparingly soluble

Group 2 - solubility of sulphates

Decrease (BaSO4 is insoluble, and therefore won't react with H2SO4 once a layer has formed around it)

Use of Magnesium

Extraction of titanium

1) TiO2 (ionic) +2Cl2 + 2C → TiCl4 (l, molecular) + 2CO at 900˚C

2)TiCl4 is purified by fractional distillation (this wouldn't work for TiO2 as ionic and solid at rtp)

3)TiCl4 (g) + 2Mg → Ti (s) + 2 MgCl2 (aq) in an Ar atmosphere at 1000˚C, can be very slow up to 2 days

4) add dilute HCl to react with excess Mg

5) purify Ti

6) extract Mg by electrolysis and reuse

Why is the extraction of titanium so expensive?

1) Mg is expensive (C can't be used as TiC will form)

2) Ar is expensive

3) batch process (clean...)

4) high temperatures and fractional distillation

The uses of Mg(OH)2

Medicine

In water it makes a weakly (sparingly soluble) solution that can be used to treat excess stomach acid, as well as to treat constipation (laxative)

Better than CaCO3 as no CO2 produced

It is also in toothpaste to neutralised acid from bacteria

The use of Ca(OH)2

Agriculture

Neutralises acid soils (important as plant growth depends on soil pH - improve yield)

The use of BaSO4

Medicine

Barium meal for patients who need their intestines X-rayed. It absorbs X-rays, and therefore gut shows up, and is not dangerous as is insoluble

Testing for Sulphate Ions - long explanation

1)Add dilute HCl or HNO3 to BaCl2 to acidify it

2)The H+ ions will react with any CO3 ions to produce CO2 and H2O - preventing a false positive

3)The Ba ions will then react with any SO4 ions and give a white precipitate

Testing for CO3 ions

Add substance to equal volume of HCl

Collect gas (e.g. using upturned test tube)

Add lime water to collected gas and shake

Milky - positive (CO2)

Testing for NH4 ions

Add solution to NaOH

Collect gas

Red litmus paper - blue (NH3)

Testing for Cl ion in a solid

Add a few drops of conc. sulfuric acid, in a fume cupboard

Test gas with blue litmus paper, goes pink due to HCl

Testing for Br ion in a solid

Add a few drops of conc. sulfuric acid, in a fume cupboard

Test gas with filter paper soaked in acidified potassium dichromate, orange to green due to SO2

Testing for I ion in a solid

Add a few drops of conc. sulfuric acid, in a fume cupboard

Test gas with filter paper soaked in lead nitrate, colourless to black due to H2S

Testing for Ca and Mg

Add NaOh

Ca - white precipitate of Ca(OH)2

Mg - blue precipitate of Mg(OH)2 (that dissolves in excess alkali)

Or, add to HCl - Ca will have a more violent reaction

Flame test for group 2 metals

Be and Mg - no colour

Ca, Sr and Ra - red

Ba - green

Testing for halide ions in solution

Add acidified (not w/ HCl) AgNO3 to solution

Precipitate forms :White - Cl, Cream - Br, Yellow - I

Add dilute ammonia: AgCl dissolves to give colourless solution

Add conc. ammonia: AgBr dissolves as well

(Ag(NH3)2+ ions and Cl/Br - ions form)

The trend in solubility of silver halides in ammonia

Decrease ((as charge density of halide ion decrease, so interactions with polar water molecules weaker))

Reaction of Cl2 with cold dilute NaOH

Cl2 + 2NaOH → NaClo + NaCl +H20

all aq (not water lol)

disproportionation reaction

Bleach - chemical formula, name and property

NaClO sodium chlorate

powerful oxidiser

Uses of bleach

bleaching wood pulp to make paper

cleaning

disinfecting

What happens when you add chlorine to water? What if you add universal indicator paper?

Cl2 + H20⇋ HClO + HCl

HCl fully dissociates to H and Cl ions

HClO partially dissociates: HClO ⇋ H + ClO

disproportionation reaction

Goes red (acid) then white (bleached by ClO- ion)

What happen when you add chlorine to water in the sunlight?

2Cl2 + 2H20 → O2 + 4HCl

2Cl2 + 2H20⇋ 2HClO + 2HCl

2HClO→ 2HCl + 02 (HClO isn't very stable

so breaks down in sunlight)

Greenish colour will fade

Uses of Cl2

Drinking water treatment

Swimming pool treatment

How does Cl2, when added to water, kill bacteria (and other pathogens)?

HClO disrupts the membrane of bacteria

HClO can then enter cell and kill it

Pros of using Cl2 to treat drinking water

Kill bacteria and prevent epidemics of bacteria like choloera

Lasting protection as stays in the water (ozone or UV do not prevent recontamination later on)

Cheap

Remove Fe by converting it to FeO(OH) which is solid and can be filtered out

Cons of using Cl2 to treat drinking water

Bad smell and taste

Does not remove nitrates

Can react with organic material (plant/animal matter) to form chloroakanes which can be carcinogenic (but only in conc.'s higher than that in water)

Pros of using Cl2 to treat swimming pools

Doesn't require UV/sun light (like its alternative hydrogen peroxide does)

Kills bacteria and prevents algae growth

Cons of using Cl2 to treat swimming pools

Some people have sensitivities to it

Higher conc. than in drinking water - cna lead to red eyes and dry skin, esp. in asthma/allergy sufferers

Why does society choose to add chemicals to drinking water?

The health benefits far outweigh the toxic effects

Other chemicals that are added to water for drinking

Aluminium sulfate - coagulant

Ca(OH)2 - reduce cloudyness

Flourine is drinking water

Naturally some, but not in high enough concentrations to be beneficial

So add as NaF in some parts

It strengthens tooth enamel - less prone to decay

But it can cause dental flourosis and/or osteoporosis in high concentrations

Group 7 boiling points

Increase - Mr of diatomic molecules increases as you go down the group, more vdw form between molecules (as more electrons, more likely to be a charge separation)

Group 7 electronegativity

Decreases - Atomic radius increases, meaning decreasing attraction from nucleus on bonding pair of electrons

The oxidising/reducing ability of the halogens increases/decreases down the group, because...

The oxidising ability decreases

(they are oxidising agents)

... atomic radius increases meaning decreased ability of the nucleus to attract and accept an electron

The oxidising/reducing ability of the halides increases/decreases down the group, because...

The reducing ability increases

(they are reducing agents)

.... ionic radius increases meaning ions more readily (more easily) donate an electron as it is less strongly attracted by the nucleus

F2

very pale yellow gas

very reactive

toxic

Cl2

greenish gas

poisonous in high concentrations

reactive

Br2

Red liquid

Brown/orange poisonous fumes

Iodine

Shiny grey/black solid that sublimes to a purple gas

Redox displacement reactions of the halogens (oxidising agents) : Cl2 (aq)

Displaces Br from solution, Br2 water forms

very pale green to orange

Displaces I from solution, I 2 water forms

very pale green to brown

Redox displacement reactions of the halogens (oxidising agents) : Br2 (aq)

Displaces I from solution, I 2 water forms

orange to brown

Does not displace Cl

Redox displacement reactions of the halogens (oxidising agents) : I 2 (aq)

Does not displace either Cl or Br

Reaction of Cl- ion with conc. sulfuric acid

NaCl(s) + H2SO4 (aq) → NaHSO4 (aq) + HCl (g)

acid base reaction

HCl does react w/ H2SO4 because it is not strong enough reducing agent to reduce S

Reaction of Br- ion with conc. sulfuric acid

NaBr(s) + H2SO4 (aq) → NaHSO4 (aq) + HBr (g)

2HBr (g) + H2SO4 (aq) → Br2(g) + SO2 (g) + 2H20(l)

2Br- → Br2 +e- //H2SO4 + 2H+ +2e- → SO2 + 2H2O

Overall: 2NaBr + 3H2SO4 → 2NaHSO4 + Br2 +SO2 +2H2O

S and H2S are not produced because Br- is not a strong enough reducing agent to reduce S further

Br2 is a red gas in this instance

Reaction of I- ion with conc. sulfuric acid

NaI(s) + H2SO4 (aq) → NaHSO4 (aq) + HI (g)

2HI(g) + H2SO4→ I2 (s) + SO2 + 2H2O

6HI(g) + H2SO4→ 3I2 (s) + S + 4H2O

8HI(g) + H2SO4→ H2S (g) + 4I2 (s) + 4H2O

Overall: 16NaI+ 19H2SO4→ 16NaHSO4 + 8I2 (s) + SO2 + S + H2S +10H2O

I2 is a black solid giving off purple fumes in this case

SO2

chocking odour, colourless, acidic

H2S

bad egg smell

S

yellow solid

Oxidation states of S

H2SO4 = 6

SO2 = 4

S = 0

H2S = -2

HF

Irritant to eyes, mucous membrane and skin

HCl, HBr or HI + NH3 (g) →

(wave bottle of ammonia over test tube of reaction of solid halide with conc. H2SO4, air must be moist)

NH4Cl/Br/I (s)

Misty white fumes

Block d (or f) element

An element that forms one or more stable ions with a partially filled d (or f) orbital

Block s (or p) element

An element with its outer electrons in the s (or p) orbitals