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.
Trend in solubility of G2 Sulfates
- The solubility of G2 metal sulfates decrease.
- BaSO₄ is insoluble
Test for Sulfate ions
- Add ACIDIFIED barium chloride
- A white precipitate (BaSO₄) will form if sulphate ions are present
- (It’s acidified using HCl to remove excess sulphites & carbonates)
Trend in Solubility of G2 hydroxides
- ↓ Group 2 the solubility of metal hydroxides increase
- G2 metals become more alkaline as you move down the group
- Magnesium hydroxide is sparingly soluble in water
Reaction of G2 metal oxides w/ water
Group 2 metal oxides react vigorously with water to give a metal hydroxide
- NO hydrogen is formed
- they form alkaline solutions
DISPROPORTIONATION of Chlorine and its uses
- 2NaOH(aq) + Cl₂(g) ⇌ NaClO(aq) + NaCl + H₂O
ox of cl: 0 +1 -1 - cold, dilute, aqueous NaOH
- DISPROPORTIONATION reaction for Bleach formation
- Cl₂(g) + H₂O ⇌ 2H(aq) + Cl(aq) + ClO(aq)
0 -1 +1
chlorate used to kill bacteria in water treatment.
forms carcinogen but benefits out way goods
Trend in rate of reaction of G2 metals w/water
- M(s) + 2H₂O —> M + 2OH + H₂
-M(s) + 2H₂O —> M(OH)₂(aq) + H₂(g)
0 +1 +2 0
-The rate of reactivity w/water of the elements increase as you move down the group. (Be - no reaction, Mg - very slow)
-G2 metals react vigorously w/steam to form an oxide. - M(s) + H₂O —> MO(s) + H₂(g)
explain in terms of structure and bonding why magnesium has a higher melting point than sodium oxide
- stronger ionic bonds
- Mg2+ ions have a higher charge
- magnesium has a smaller ionic radius than sodium.
What series of tests can a student do to show a solution contains ammonium sulfate?
warm with NaOH
- Damp red litmus paper at the MOUTH of the tube turns blue.
add Barium Chloride to it within an acidified solution
- white precipitate forms
Test for Sulfate ions
Sulfate anions can be tested for by the displacement of barium ions. If a small amount of barium chloride solution is added to an acidified solution of sulfate ions, a displacement reaction takes place in which the barium ions displace the cation in the sulfate compound to form a white precipitate of barium sulfate.
