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A Level Chemistry > Periodicity, Group 2 & 7 (+redox3.17) > Flashcards

Periodicity, Group 2 & 7 (+redox3.17) Flashcards

1
Q

What happens to atomic radius across a period?

A

It decreases

  • as the number of protons increases and nuclear charge increases
  • this means electrons are pulled closer to the nucleus making the atomic radius smaller
  • shielding stays roughly the same
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2
Q

What happens to atomic radius down group 2?

A

It increases because extra electron shells are added

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3
Q

What is the general trend in first ionisation energy down a group?

A

It decreases:
- electrons have more shielding
- outer electrons further away from the nucleus so weaker attraction
- so easier to remove outer electrons

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4
Q

What happens to the reactivity and melting points down group 2?

A

Reactivity - increases
Melting points - decrease

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5
Q

What are the uses of group 2 elements?

A

CaOH - agriculture (neutralises acid soils)
MgOH - indigestion tablets (neutralises stomach acid)
BaSO4 - barium meals

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6
Q

What is the trend in boiling point down group 7 and why

A

Increase down the group

  • Size of atom increases as more occupied electron shells
  • stronger van der waals forces of attraction between molecules take more energy to break
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7
Q

What’s the trend in electronegativity down group 7 and why

A

Decreases down group
- more occupied electron shells
- greater atomic radius and outer electrons are further from the positive charge of the nucleus
- lower force of attraction between the nucleus and electron pair in the covalent bond

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8
Q

What do you use to test for halide ions?

A

Acidified AgNO3 (silver nitrate)

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9
Q

Why do you add HNO3 and not HCl

A
  • to remove CO3(2-)
  • adding HCl would add Cl- ions giving a false positive result
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10
Q

What is the trend in oxidising ability down group 7 (4m)

A

Decreases down group
- Cl has fewest occupied electron shells
- greatest force of attraction between outer electrons and nucleus
- easiest to gain electrons and be reduced —> best oxidising agent

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11
Q

What’s the equation for Cl2 oxidising 2I-

A

Cl2 + 2I- —> 2Cl- + I2

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12
Q

Why does chlorine make drinking water safe

A
  • forms CIO- ions which oxidise all microorganisms in water
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13
Q

What’s the trend in hydroxide solubility down group 2

A

Increases down the group
- Mg(OH)2 is almost insoluble
- Ba(OH)2 creates a strong alkaline solution

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14
Q

What’s the trend in sulfate solubility down group 2

A

Decreases down the group
- MgSO4 is soluble
- BaSO4 is insoluble

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15
Q

What’s the trend in melting point down group 2

A

Decreases down the group because atom size gets bigger
- because sea of delocalised electron is further from the positive charge of the nucleus—> weaker metallic bonds which take less energy to weaken

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16
Q

What’s the equation for the extraction of titanium using magnesium

A

TiCl4 + 2Mg —> 2MgCl2 + Ti
role of Mg is reducing agent

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17
Q

What are electron acceptors?

A

Oxidising agents (loss of electrons)

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18
Q

What are electron donors

A

Reducing agents (gain of electrons)

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19
Q

Reduction is the —— of hydrogen?

A

Gain

20
Q

Oxidation is the —— of hydrogen?

A

Loss

21
Q

Reducing agents get ———?

A

Oxidised

22
Q

Oxidising agents get ———?

A

Reduced

23
Q

What’s the oxidation state of elements on their own

A

0

24
Q

What’s the oxidation state of group 1 metals

A

+1

25
Q

What’s the oxidation state of group 2 metals

A

+2

26
Q

What’s the oxidation state of aluminium

A

+3

27
Q

What’s the oxidation state of Flourine

A

-1

28
Q

What’s the oxidation state of group 7

A

-1

29
Q

What’s the oxidation state of Hydrogen

A

+1 (except when in a metal hydride eg NaH)

30
Q

What’s the oxidation state of oxygen

A

-2 (except H2O2)

31
Q

What happens (+equations) to each of the silver halide precipitates when dilute/conc NH3 are added

A

AgCl (s) + 2NH3(aq) -> Ag(NH3)2+(aq) + Cl- (dissolves in both conc+dilute)

AgBr(s) + 2NH3(aq) -> Ag(NH3)2+(aq) + Br- (only dissolves in conc)

Iodine doesn’t dissolve in either

32
Q

What’s the risk of adding chlorine to drinking water

A

Chlorine is toxic and damages the respiratory system or can cause carcinogens with hydrocarbons

33
Q

What’s the equation for the reaction of Cl2 with cold water

A

Cl2 + H20 -> HClO + HCl (reversible reaction arrow)

34
Q

What type of reaction is chlorine + water

A

Disproportionation: chlorine is both oxidised and reduced

35
Q

What’s the equation for making bleach?

A

Cl2 + 2NaOH -> NaCl + NaCIO + H20

36
Q

What’s the equation for the reaction of chlorine and water in the presence of sunlight

A

2Cl2 + 2H20 -> 4HCl + O2

37
Q

If an elements oxidation state increases it has been —-?

A

Oxidised (lost electrons)

38
Q

If an elements oxidation state decreases it has been —-?

A

Reduced (gained electrons)

39
Q

Why do melting points increase across period 3 metals

A
  • cation charge increases
  • so more delocalised electrons
  • so more electrostatic attraction
40
Q

Describe all the halogens Flourine, chlorine, bromine and iodine at room temp

A

F2 - pale yellow gas
Cl2 - pale green gas
Br2 - brown liquid
I2 - grey solid

41
Q

Describe why ionisation energy drops across period 3 between Mg and Al (the 1st dip)

A
  • Al’s first I.E is lower than Mg
  • because unlike Mg whose electron is removed from the 3s sublevel, Al electron is removed from the 3p sublevel
  • which is further away from the nucleus and has more shielding by 3s electrons
  • so Al’s electron requires less energy to remove
42
Q

Describe why ionisation energy drops across period 3 between phosphorus and sulfur (2nd dip)

A
  • S first I.E is lower than P
  • because unlike P whose electron in the 3p sublevel are unpaired, S has a pair of electrons in one of its 3p orbitals
  • paired electrons repel each other more than unpaired
  • so less energy is required to remove an electron from sulfur
43
Q

Equations for Ca, Sr and Ba with water

A

Ca + 2H20 (I) Ca(OH)2(aq) + H2(g)
Sr + 2H20 (I) Sr(OH)2(aq) + H2(g)
Ba + 2H20 (I) Ba(OH)2(aq) + H2(g)

44
Q

Equation for use of CaO in removing SO2 from flue gases

A

SO2 + CaO —> CaSO3

45
Q

Explain why successive ionisation energies increase

A

Because electrons are removed from an increasingly positive ion which requires more energy

46
Q

How does the graph of first ionisation energies give evidence for shells

A

The electron is being removed from an inner shell

47
Q

What is the general trend in first ionisation energy across a period

A

It increases:
- nuclear charge increases
- shielding stays roughly the same
- outer electron more strongly attracted to nucleus
- so harder to remove

A Level Chemistry (13 decks)

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