Topic 4 - INORGANICS Flashcards
Why does ionisation energy decrease down group 2?
- Outer electron is in a successively higher energy level
- Distance and shielding both increase
- (Even though nuclear charge increases)
- Attraction between outer electron and nucleus is weaker
What is the trend in reactivity down group 2?
‘Reducing strength’ increases down group 2
- The sum of 1st and 2nd ionisation energies decreases
- The strength of metallic bonding decreases
What is the trend in hydroxide solubility down group 2?
Group 2 hydroxides become more soluble down the group
What is the trend in sulphate solubility down group 2?
Group 2 sulphates become less soluble down the group
Group 2 metal + oxygen –> ?
Group 2 metal oxide
Are group 2 elements oxidised or reduced when reacted with something?
Always oxidised
- They gain a 2+ charge
What are the properties of a group 2 metal oxide?
- Ionic compound
- White solid
- High melting point
Group 2 metal + chlorine –> ?
Group 2 metal chloride
What are the properties of a group 2 metal chloride?
- Ionic compound
- White solid
- High melting point
Group 2 metal + water –> ?
Group 2 metal hydroxide + hydrogen
What are the observations of a reaction between a group 2 metal and water?
- Effervescence
- Metal disappears
- Delayed white precipitate with Ca(OH)2
Group 2 metal oxide + water –> ?
Group 2 metal hydroxide
What are the observations of a reaction between a group 2 metal oxide and water?
White precipitate formed with Mg(OH)2 and Ca(OH)2
Group 2 metal oxide + acid –> ?
Salt + water
Why does CaCO3 thermally decompose?
- Ca2+ ion polarises the CO3 2- ion
- The lower electron density at the other end of the CO3 2- ion weakens a C-O bond
- When provided with heat, the bond breaks
Why do nitrates thermally decompose?
- The cation polarises the NO3- ion
- The lower electron density at the other end of the NO3- ion weakens an N-O bond
- When provided with heat the bond breaks
Are group 1/2 carbonates/nitrates more or less thermally stable down the group?
More stable
Why are group 1/2 carbonates + nitrates more thermally stable down the group?
- Cation radius increases
- Cation polarises CO3 2-/NO3- less
- C-O/N-O bonds are weakened less
- Either they break more slowly, or they need a higher temperature to break
What are the observations of group 1/2 carbonate decomposition?
- Limewater turns cloudy
What are the observations of group 1/2 nitrate decomposition?
- Glowing splint relights
- Brown fumes
What is the trend of melting/boiling point down group 7?
Melting/boiling point increases down the group
Why does melting/boiling point increase down group 7?
- More electrons per halogen molecule
- Stronger London forces between molecules
- More energy required to overcome IMFs
How does state of matter vary down group 7?
- Fluorine: Gas
- Chlorine: Gas
- Bromine: Liquid
- Iodine: Solid
How does colour change down group 7?
Colour becomes darker down the group
Pale yellow->grey
Why do halogens dissolve poorly in water?
- London forces are broken in ‘X2’
- Hydrogen bonds are broken in H2O
- Only London forces are formed between X2 and H2O
- IMFs broken are stronger than IMFs formed
Why do halogens dissolve well in hydrocarbon solvents?
- London forces are broken in ‘X2’
- London forces are broken in HC
- London forces are also formed between X2 and HC
- IMFs broken are similar to IMFs formed
What is the trend in electronegativity down group 7?
Electronegativity decreases down group 7
Why does electronegativity decrease down group 7?
The bonding electron pair is:
- Further from the nucleus
- Better shielded from the nucleus
Hence the attraction between the nucleus and bonding electron pair is weaker
Are group 7 elements oxidised or reduced when reacted with something?
Reduced
- Gain a 1- charge
What is the trend with reactivity of group 7 elements down the group?
Oxidising strength increases up the group
This is because the incoming electron is:
- Closer to the nucleus
- Less shielded from the nucleus
What is a halogen displacement reaction?
When a more strongly oxidising halogen can oxidise the halide ions of less strongly oxidising halogens
What colours are Cl2, Br2 and I2 in organic solutions?
- CL2: pale green
- Br2: red
- I2: Purple
What colours are Cl2, Br2 and I2 in aqueous solutions?
- Cl2: pale green
- Br2: yellow/orange
- I2: brown
What are the products of a chlorine disproportionation in water?
Cl2 + H2O –> ?
HCl + HClO
What are the products of a chlorine disproportionation in cold, dilute alkali (NaOH)?
Cl2 + 2NaOH –> ?
NaCl + NaClO + H2O
What are the products of a chlorine disproportionation in hot, concentrated alkali (NaOH)?
3Cl2 + 6NaOH –> ?
5NaCl + NaClO3 + 3H2O
What state are hydrogen halides at room temp and pressure?
Gases
Observations of the reaction between hydrogen halides + air + ammonia?
- Steamy white fumes
- Damp blue litmus paper turns red
+ Ammonia
- Dense white smoke
What is the trend in reactivity in halide ions?
Reducing strength increases down the group
Why does reducing strength increase down the group of halide ions?
Outer electron is:
- Further from nucleus
- Better shielded from nucleus
- Less strongly attracted by nucleus
NaCl + H2SO4 –> ?
What are the observations?
NaHSO4 + HCl
- Effervescence
- Steamy white fumes
- White solid
- Damp blue litmus paper turns red
HCl cannot reduce NaHSO4 any further
2HBr + H2SO4 –> ?
What are the observations?
Br2 + SO2 + 2H2O
- Brown liquid
- Orange fumes
NaI + H2SO4 –?
What are the observations?
HI + NaHSO4
- Effervescence
- Steamy white fumes
- White solid
- Damp blue litmus paper turns red
HI is a strong enough reducing further to then reduce NaHSO4
8HI + H2SO4 –> ?
What are the observations?
4I2 + H2S + 4H2O
- Grey solid
- Purple fumes
What is the chemical test for the presence of halide ions?
- Add dilute nitric acid
- Then add silver nitrate
What are the observations of the chemical test for the presence of halide ions?
- Cl2: white precipitate
- Br2: cream precipitate
- I2: yellow precipitate
What chemical is added to distinguish between halide precipitates, and what are the observations?
Ammonia solution
- AgCl: ppt disappears
- AgBr: ppt disappears in concentrated ammonia
- AgI: no change
What colours are the flames according to group 1/2 cations?
Li+: Red
Na+: Yellow
K+: Lilac
Ca2+: Brick red
Sr2+: Red
Ba2+: Green
What is the chemical test for chlorine?
Damp blue litmus paper turns white
What is the chemical test for carbonates?
- Add HCl
- Bubble through limewater; if limewater turns cloudy, carbonates are present
What is the chemical test for sulphates?
Chemical test for carbonates, then:
- Add barium chloride
- If sulphates are present, white ppt formed
What is the chemical test for ammonium?
- Add dilute sodium hydroxide
- Damp blue litmus paper turns red
What is the theory behind flame tests?
- Electron absorbs heat energy and is promoted to a higher energy level
- The electron is unstable in the higher energy level
- The electron drops back to a more stable energy level by emitting a photon
What are the disadvantages of using chlorine to sterilise water?
- Toxic in excess
- Can react with hydrocarbons to produce carcinogens
