Group 2 & Group 7 Flashcards
Group 1 & Group 2 have the same trends
Atomic Radius
- Down G2, INCREASES
↳ more QL = more electrons →electrons are further away : easier to remove
Ionisation Energy
- Down G2, DECREASES
↳ more QL = further away electrons →easier to remove : less energy needed
Mp/Bp
- Down G2, DECREASES
↳ atomic radius increases = outershell has lower nuclear charge (between cation & electron)
↳ less energy is needed to break this making the mp/bp lower
Reactivity to water
- Down G2, increases
↳ atomic radius increases = outer electron is further away
↳ reacts w water easily
G2 react w water produce HYDROXIDES
G2 burn in oxygen forming OXIDES
G2 react w chlorine forming CHLORIDES
Trend
Every G2 elements form ionic bonds except Berilium which forms covalently
* BeO doesn’t react w water (exception)
* MgO reacts slowly w water
Down G2, reactivity increases
- Alkaline solutions become stronger
↳ the hydroxide ions become more soluble
-hydeoxides form more quickle : the pH of the solution goes above 7
G2 Oxides react w water
G2 Oxides react w dilute acid
Solubility Trend
Hydroxide
Down G2, increases in hydroxide ions (OH)
* more soluble : pH goes above seven
↳ meaning that it will dissolve faster
Solubility Trend
Sulfate
Down G2, decreases in sulfate ions (SOv4 -2)
* become less soluble
↳ dissolve slower
Thermal Stability
Applied heat needed to break something down
Large ions are Destabilised/Polarised/Distorted by cations
Carbonates/Nitrates
They’re broken down by negative ions
Thermal Stability
Trend 1)
Greather distortion = more unstable the compound
Thermal Stability
Trend 2)
Larger cations = smaller distortion than small cations
↳lower charge density
-down G2 atomic radius increases
↳ electrons = further away & ion can’t hold onto them
↳ if it can’t even do this, then it can’t pull another’s electrons
Charge Density
Charge per space/ Charge over smaller space
Larger cation = lower CD
↳ less distortion = more stable the nitrate/carbonate compound
Top G2 = most polarising
Smaller atomic radius = more polarising
Higher charge = more polarising
G2 cations have a 2+ charge compared to a +1 from G1 so G2 carbonates/nitrates = less stable than G1
Anions
Thermal Stability Testing
Nitrate Decomposition
- Test to see how long it takes for a certain amount of O2 to be released
Glowing splint relights if positive
- Test to see how long it takes for NO2 to form
NO2 gas is brown
Anion
Thermal Stability Testing
Carbonate Decomposition
- Test to see how long it takes for a certain amount of CO2 t be released
Limewater goes cloudy if positive
Cation
Flame Test
Equipment
- HCl
- Metal solutions (cations)
- Nichrome wire
- Bunsen Burner
Cation
Flame Test
Practical done because some metals have the same colour
- Take nichrome wire & dip into HCl
- Put that wire into flame
↳ step 1 & 2 cleans loop - Dip wire into one of the metal solutions
- Place that wire into the flame at 45° just below top of the flame for 5 secs
- Observe colour & note it down
- Repeat 1-8 until you’re done w all solutions
- Repeat procedure again for each solution
↳ some reactions occur quickly : recheck colour
!!If all tests are orange, your test is contaminated!!
Colours of metal ions
G1
* Li+ = red
* Na+ = yellow/orange
* K+ = lilac
* Rb+ = red
G2
* Ca2+ = red
* Sr2+ = crimson red
* Ba2+ = green
neither
* Cu2+ = blue/green
Down G7 = less reactive
As they’re reduced, they oxidise another substance (oxiding agents)
- Larger G7 atoms are less reactive : reactivity decreases down the group (electronegativity)
↳ due to increase in QL
Down G7 = Mp/Bp increase
Mp
Down G7, states change
↳ more energy is needed to break bonds
Bp
Down G7, there are more QL : more electrons
↳ more London Forces
↳ more energy needed to break these
Group 7 Properties Table
G7 Properties by theirselves
- Diatomic
- Non-polar
↳ can’t form ions : they can’t carry a charge : can’t conduct electricity or dissolve in water
↳ but can dissolve in organic compounds i.e. HEXANE
G7 Colours
Halide
Charged halogen
Displacement
Where an element replaces another in a compound
Halogens can displace halide ions from solutions
The more reactive the halogen, the more able it is to displace a less reactive halide
↳ they have a higher oxidation strength
- The colour expressed within the solution = the colour of the uncombined halide
Halogens can react w G1 & G2 metals
Disproportionation w Cold Alkali
Sodium Hydroxide
g + aq → aq + aq + l
Disproportionation w Cold Alkali Example
Chlorine & Sodium Hydoxide
- Make bleach
↳ bleach is used in water treatment & textiles
Disproportionation w Hot Alkalis
g + aq → aq + aq + l
HALIDES lose electrons if there’s less of a pull from nucleus & outer electron is weak
Down G7 = attraction weaker
- Atomic radius increases : electrons are further away
↳ there’s more shielding from inner electrons
All halides react w CONCENTRATED sulfuric acid to give a hydrogen halide
Concentrated Sulfuric Acid = always liquid
Reaction of KF/KCl w H2SO4
- Oxidation number for Sulfur doesn’t change
↳ F- & Cl- ions aren’t strong enough reducing agents to reduce Sulfur’s oxidation number - This reaction isnt redox as the oxidation number of the halide & sulfur remain the same
- Produce misty fumes
Reaction of KBr w H2SO4
- 2nd reaction occurs instantly after 1st
- HBr dissolves in the solution bc it isn’t isolated
- HBr produces mistry fumes
Br gives its electron more easily to S & drops S down to ox. no° 4
↳Br is a stronger reducing agent than Cl- & F- bc it has more electrons
↳ this is redox reaction as ox. no° change
Reaction of KI w H2SO4
- 3 reactions
1. 1st reaction occurs
2. 2nd reaction occurs instantly after
3. 1st reaction isn’t stopped : reoccurs
4. 3rd reaction produced slightly after
Summary
Strength of reducing agents increases → causing S ox. number to decrease
Flourine/Chloride
+6 → +6
Bromide
+6 → +4
Iodide
+6 → +4 -2
Test for Halides
- Add nitric acid
↳ removes interface ions - Add silver nitrate solution
- A precipitate of a silver halide will form
Precipitate colour based on Halide
Precipitate- solid that doesn’t dissolve in a liquid
Flourine = none formed
Chloride = white
Bromide = cream
Iodide = yellow
To confirm test for Halides
- Add ammonia (NH3)
↳ it is sometimes difficult to see precipitate based on te halide test
↳ ammonia allows verification
Dilute Ammonia
* Only breaks down the precipitate in AgCl into a solution
* Unaffects AgBr & AgI
Concentrated Ammonia
* Only breaks down precipitate in AgBr into a solution
* Unaffacts AgI
AgI is unaffected by both types of ammonia
Polyatomic Ions
Carbonates (CO2)
- If heated or HCl is added it breaks the solution down
- CO2 is given off
↳ collect it & put into limewater
Positive Test: turns cloudy
Polyatomic Ions
Sulfate (SO4 2-)
- Use HCl
↳ removes contaminates - Followed by BaCl
↳ produces BaSO4 (contains sulfur)
Positive Test: white precipitate present
Ammonium Compounds
(NH4 +)
- NH3 can be detected using damp red litmus paper
↳ turns blue - For NH4+ add NaOH & heat gently
↳ gives off NH3 gas (litmus paper test + smells)
If NH3 is involved, NH4 ions are present in sample
