Group 2, Group 7, Periodicity Flashcards
Testing AS level inorganic chemistry
Group 2
Elements Reaction w/ Oxygen
- Burn and Form Metal OXIDES
- REDOX reaction
- Oxygen is an oxidising agent
- ## G2 elements are reducing agents
- They all form white solid precipitates
Which molecule has a lower boiling point, Chlorine or Bromine?
And why?
- ## Chlorine is smaller than bromine / has fewer electrons
- ## The forces between chlorine molecules are weaker.
- Less Vander Waals forces between molecules
What reagent react with aqueous silver nitrate & what do they form?
- Any soluble bromide < cream precipitate formed
- Any soluble chloride < white precipitate formed
- Any soluble Iodide < yellow precipitate formed
- NaOH, KOH < brown precipitate formed
- any soluble carbonate < solid/precipitate formed
What happens to the atomic radius across a period?
- The atomic radius decreases slightly as you go across a period.
- ∵ INCREASE nuclear charge so the nucleus pulls the outer electrons closer, decreasing radius.
Trend in melting points down Group 2?
- melting point ↓ down group
- Down group radius of metal ions increase but no. of delocalised electrons stay the same per atom, same with the +2 charge.
- Greater distance between delocalised electron and positive nuclei
- ∴ less energy needed to break bond.
Trend in First Ionisation Energy across a group
- ↑ atomic radius
extra electron shell for each element down group. - less attraction between outermost electron and nucleus.
- ↑ shielding greater no. of inner electron shells.
Trend in Ionisation Energy across a period
- Same no. of electron shells
- ↑ nuclear charge
- ↓ Atomic radius
- ↑ Ionisation Energy
Industry uses of Group 2 metals
Titanium metal extraction
↳ TiCl₄ is reduced by Magnesium(Mg)
TiCl₄(l) + 2Mg(s) —-> Ti(s) + 2MgCl₂(s)
Acid Neutralisation: Ca(OH)₂ (slacked lime) in agriculture, Mg(OH)₂ in medicine (for excess stomach acid)
X-rays - Barium meal, opaque on x-rays, insoluble BaSO₄
Wet Scrubbing - CaO/CaCO₃, used to remove acidic SO₂ from flue gases.
CaO(s) + 2H₂O(l) + SO₂(g) —-> CaSO₃ + 2H₂O(s)
Halides reaction with sulfuric acid.
NaF/NaCl
NaCl(s) + H₂SO₄ (l) —-> Na₂HSO₄ + HCl(g)
- misty fumes, F & Cl have a weak reducing power, reaction stops here
NaBr
NaBr + H₂SO₄ —> NaH₂SO₄ +HBr
2HBr + H₂SO₄ —> Br₂(g) + SO₂(g) + 2H₂O(l)
+6 +4 -> reduction
-1 0 -> oxidation
- orange fumes
NaI -
“” - reduces further than Br
6HI(aq) + SO₂(g) —> H₂S(g) +3I₂(s) + 2H₂O(l)
+4 -2 -> reduction
-1 0 -> oxidation
Test for Halides
Acidified Silver Nitrate
Ag⁺(aq) + X⎺ (aq) —-> AgX(s)
+ add nitric acid to remove excess ions
colours:
F⎺ - None Cl⎺ - White Br⎺ - Cream I⎺ - Yellow
Ammonia
↳ added to precipitate to be certain
AgCl —> dissolves in DILUTE ammonia
AgBr —> dissolves in CONCENTRATED ammonia
AgI —-> insoluble in ammonia
Trend in Reducing Power of Halides
- Group reducing power of halides increases.
- halide will lose outermost electron ∴ dependent on shielding and IONIC radius.
- The greater the reducing power of a halide, the more easily it loses electrons.
- reactions of halides with H₂SO₄ can be used to compare reducing power.
Trend in oxidising power of Halogens
+ How do you test oxidising ability?
- As the halogens become less reactive down the group, their oxidising ability decreases.
Test oxidising ability:
- Displacement reaction
_ In Aqueous solution halogens higher up in group will displace a halide.
e.g. Cl₂(g) + 2Br⎺ (aq) —> 2Cl⎺ (aq) + Br₂(g)
- can also be used to identify halogen present by colour
Bond Strength Trend
VS
Electronegativity Trend
in Halogens
- Low bond energies = easy to break covalent bonds in diatomic molecules.
- Group Bond energies decrease ∵ increased shielding ∴ reduced attraction between nuclei and shared pair of electrons.
- Group electronegativity decreases ∵ atomic radius increases + increased shielding ∴ reduced attraction between halogen atoms & atoms of other elements
Solubility of Halogens
- poorly soluble in water
- soluble in organic compounds. - e.g. hexane
in Water Organic solvent
Cl₂ colourless colourless
Br₂ yellow/orange orange/Red
I₂ brown Pink/Violet
Trend in Boiling Point of the Halogens
- ↓ Group boiling point of the G7 elements increases
_ The larger the molecule, the more electrons present ∴ stronger van der waals forces. - ↓ group melting point also increases
- ↓ group the volatility of the elements decrease.
Test for Ammonium ions
Ammonium cations can be tested for by mixing the unknown compound with warm, dilute NaOH (aq). If ammonium ions are present, ammonia gas will be given off, turning damp red litmus paper blue.
Test for Group 1 & 2 ions
flame tests
Test for Halide ions
- Halide ions can be tested for by mixing the unknown compound with acidified silver nitrate solution.
- A halogen-specific precipitate will form
- Concentrated ammonia solution can then be added.
- Different silver halides will have different solubilities. Some silver halide precipitates will re-dissolve upon addition of ammonia solutions but others will not.
