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Chemistry A-Level > Reactivity Trends (Chapter 8) > Flashcards

Reactivity Trends (Chapter 8) Flashcards

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1
Q

What is the name for the Group 2 metals?

A

The alkaline earth metals - because of the alkaline properties of their metal hydroxides

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2
Q

How are Group 2 metals found?

A

They are reactive and do not occur in their elemental form naturally - found in stable compounds e.g. CaCO3

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3
Q

What is a general formula for the electron configuration of Group 2 metals

A

[nearest noble gas] (period number)s2

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4
Q

Explain the electron configuration of Group 2 metals

A
  • Each Group 2 element has 2 outer shell electrons, two more than the electron configuration of a noble gas
  • Therefore, 2 electrons are in the outer s sub-shell
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5
Q

What is the electron configuration of the Group 2 ions?

A

The nearest noble gas

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6
Q

What happens in redox reactions of Group 2 metals?

A

Each metal atom is oxidised, losing 2 electrons to form a 2+ ion - Group 2 element is a reducing agent
e.g. Ca = Ca2+ + 2e-

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7
Q

What happens in redox reactions of Group 2 metals with oxygen?

A

They react with oxygen to form a metal oxide with the general formula MO, made up of M2+ and O2- ions
e.g. 2Mg + O2 = 2MgO (white solid)

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8
Q

What happens in redox reactions of Group 2 metals with water?

A

They react with water to form an alkaline hydroxide with the general formula M(OH)2 and H2
e.g. Mg + 2H2O = Mg(OH)2 + H2 - reaction becomes more vigorous down the group

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9
Q

What happens in redox reactions of Group 2 metals with dilute acids?

A

They react with dilute acids to form a salt and hydrogen

e.g. Mg + 2HCl = MgCl2 + H2

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10
Q

Does reactivity increase or decrease down Group 2?

A

Increase

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11
Q

Why does reactivity increase down Group 2?

A

1) The atoms of Group 2 elements react by losing electrons to form 2+ ions
2) The formation of 2+ ions from gaseous atoms requires the input of two ionisation energies
3) The ionisation energy decreases down the group because the attraction between the nucleus and outer electrons decreases as a result of increasing atomic radius and increasing shielding effect
4) Therefore, electrons are lost more easily and the Group 2 elements become more reactive and stronger reducing agents down the group

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12
Q

What happens when Group 2 oxides react with water?

A

They release OH- ions and forming alkaline solutions of the metal hydroxide
e.g. CaO(s) + H2O = Ca2+(aq) +2OH-(aq)

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13
Q

How soluble are the Group 2 hydroxides?

A

They are only slightly soluble in water so when the solution becomes saturated, any further metal and OH- ions form a solid precipitate
e.g. Ca2+(aq) + 2OH-(aq) = Ca(OH)2(s)

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14
Q

How does the solubility of the Group 2 hydroxides change down the group?

A
  • The solubility of the hydroxides in water increase down the group
  • Therefore, the resulting solutions contain more OH- ions and are more alkaline
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15
Q

What is the pH of Mg(OH)2 solution and why?

A

Roughly 10 - it is very slightly soluble, therefore the solution has a low concentration of OH- ions

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16
Q

What is the pH of Ba(OH)2 solution and why?

A

Roughly 13 - it is much more soluble, therefore the solution has a greater concentration of OH- ions

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17
Q

What is the general trend down Group 2?

A

Solubility, pH, alkalinity and reactivity increases

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18
Q

What are the two main uses of Group 2 compounds as bases (oxides, hydroxides and carbonates) and why?

A

1) Agriculture
2) Medicine
- Their basic properties and ability to neutralise acids

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19
Q

How are Group 2 compounds used in agriculture?

A

Ca(OH)2 is added to fields as lime by farmers to increase the pH of acidic soils - the Ca(OH)2 neutralises the acid in the soil
- Ca(OH)2(s) + 2H+ = Ca2+(aq) + 2H2O

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20
Q

How are Group 2 compounds used in medicine?

A

Group 2 bases e.g. Mg(OH)2 and CaCO3 are often used as antacids in indigestion tablets for treating acid indigestion
- the acid in your stomach is mainly HCl and Mg(OH)2 and CaCO3 help to neutralise some of the acid
e.g. Mg(OH)2(s) + HCl = MgCl2(aq) + 2H2O
CaCO3(s) + 2HCl = CaCl2(aq) +H2O + CO2

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21
Q

What are the halogens?

A

Group 17/7

The most reactive non-metallic group

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22
Q

How do the halogens occur on earth?

A

As stable halide ions dissolved in sea water or combined with Na/K as solid deposits

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23
Q

How do the halogens exist at RTP?

A

As diatomic molecules

24
Q

What do the halogens form in their solid states?

A

Lattices with simple molecular structures

25
Q

What does fluorine look like at RTP?

A

Pale yellow gas

26
Q

What does chlorine look like at RTP?

A

Pale green gas

27
Q

What does bromine look like at RTP?

A

Red-brown liquid

28
Q

What does iodine look like at RTP?

A

Shiny grey-black solid

29
Q

Why is there an increase in the boiling point down the group of halogens?

A
  • More electrons therefore stronger London forces
  • Therefore more energy is required to break/overcome the intermolecular forces
  • Therefore boiling point increases
30
Q

What is the general formula for the end of the electron configuration of the halogens?

A

(period number)s2(period number)p6

31
Q

Explain the electron configuration of the halogens

A

Each halogen has 7 outer shell electrons

- therefore, 2 electrons in the outer s sub-shell and 5 electrons in the outer p sub-shell

32
Q

What is the electron configuration of a halide ion?

A

[nearest noble gas]

33
Q

What happens in redox reactions of the halogens?

A

Each halogen atom is reduced, gaining one electron to form a 1- halide ion - the halogen is the oxidising agent
- e.g. Cl2 + 2e- = 2Cl-

34
Q

What do the results of halogen-halide displacement reactions show?

A

That the reactivity of halogens decreases down the group

35
Q

Describe how you would carry out a halogen-halide displacement reaction

A

1) A solution of each halogen is added to aqueous solutions of the other halides e.g. Cl2(aq) is added to Br-(aq) and I-(aq)
2) Add an organic non-polar solvent e.g. cyclohexane and shake the mixture

36
Q

Why do you add cyclohexane to the reaction mixture?

A
  • Because solutions of iodine and bromine in water an appear a similar orange-brown colour
  • The non-polar halogens dissolve more readily in cyclohexane than water
  • In cyclohexane the colours are easier to tell apart
37
Q

What colours are bromine and iodine in cyclohexane?

A

Bromine: orange
Iodine: violet

38
Q

What are the results of the halogen-halide displacement reactions?

A

1) Chlorine reacts with BOTH Br- and I-
2) Bromine only reacts with I-
3) Iodine does not react

39
Q

What is the equation of the reaction of chlorine with bromide ions?

A

Cl2(aq) + 2Br-(aq) = 2Cl-(aq) + Br2(aq)

- Chlorine is reduced, bromine is oxidised

40
Q

Do the halogens become more or less reactive down the group?

A

Less reactive

41
Q

Why does reactivity decrease down the group of halogens?

A

1) In redox reactions, halogens react by gaining an electron
2) Down the group, atomic radius increases
3) There are more inner shells so therefore shielding increases
4) Therefore there is less nuclear attraction between the nucleus and the outer shell to capture an electron from another species
5) Therefore down the group, reactivity decreases and the halogens become weaker oxidising agents

42
Q

Why don’t we really consider fluorine and astatine?

A

Fluorine is very reactive with almost any substance it comes into contact with
Astatine is very rare because it is radioactive and decays rapidly

43
Q

What is a disproportionation reaction?

A

A redox reaction in which the same element is both oxidised and reduced
e.g. chlorine + water/cold, dilute NaOH

44
Q

Describe the disproportionation reaction of chlorine and water

A
  • When small amounts of chlorine are added to water, a disproportionation reaction takes place
  • For each chlorine molecule, one atom is oxidised and the other is reduced
  • Cl2(aq) + H2O = HClO(aq) + HCl
45
Q

What is the oxidation number of chlorine in HClO?

A

+1

46
Q

What is the name of HClO?

A

Chloric (I) acid

47
Q

What kills the bacteria, if not chlorine?

A

Chloric (I) acid and chlorate (I) ions (ClO-)

48
Q

What is chloric acid?

A

A weak bleach (bleaches indicator paper after turning it red)

49
Q

What is the disproportionation reaction of chlorine with water limited by?

A

The low solubility of chlorine in water

50
Q

What makes the chlorine more soluble?

A

If the water contains dissolved NaOH, much more chlorine dissolves

51
Q

Describe the disproportionation reaction of chlorine and NaOH

A

Cl2(aq) + 2NaOH(aq) (cold and dilute) = NaClO(aq) + NaCl(aq) + H2O
- The resulting solution contains a large concentration of ClO- ions

52
Q

What is the name of NaClO?

A

Sodium chlorate (I)

53
Q

What is NaClO used as?

A

Household bleach

54
Q

What is the main use of chlorine?

A

In water purification (sterilisation)
- It is used as a disinfectant for drinking water treatment so reduces the incidence of water-borne diseases as it kills harmful bacteria

55
Q

What are the risks of chlorine use?

A

1) Chlorine is an extremely toxic gas
2) It is a respiratory irritant in small concentrations and in large concentrations it can be fatal
3) Chlorine in drinking water can react with organic hydrocarbons e.g. methane, formed from decaying vegetation - the chlorinated hydrocarbons formed are suspected of causing cancer

56
Q

What are the benefits of chlorine use?

A

1) It ensures that our water is fit to drink and that bacteria are killed - without chlorine, the quality of drinking water would be compromised and diseases e.g. typhoid and cholera might break out
2) Safe drinking water is essential - first concern after natural disasters
3) Therefore the benefits outweigh the risks

57
Q

Describe the precipitation reactions of halide ions

A
  • Aqueous halide ions react with aqueous silver ions to form precipitates of silver halides
  • Ag+(aq) + X(aq) = AgX(s)
  • This reaction forms the basis for a test for the presence of halides

Chemistry A-Level (27 decks)

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