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1
Q

Trends in Group 2:

Atomic radius

A

Atomic radius INCREASES as you go down the group

As you go down group, a full energy level of electrons are added between each element

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2
Q

Trends in Group 2:

1st Ionisation energy

A

1st ionisation energy DECREASES as you go down the group

All outer electrons are in a full s orbital

Shielding increases, so effective charge on nucleus decreases

This causes a decrease in the attraction to the outer electrons, therefore, less energy is needed to remove it

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3
Q

Trends in Group 2:

Melting/boiling points

A

Melting/boiling points DECREASES as you go down the group

All form 2+ ions in a metallic structure

Increased shielding causes weaker effective nuclear charge

This leads to a decrease in the strength of the electrostatic attractions with delocalised electrons

Therefore, less energy is needed to overcome them, so melting/boiling point is lower

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4
Q

Group 2 elements and water:

Reactivity of group 2 elements

A

Reactivity of group 2 elements INCREASES, as you go down the group

Group 2 metals are oxidised , as they lose 2 electrons when they react

Ionisation energies decrease as you go down the group, so the outer electrons are lost more easily

This is due to the increased shielding which causes a lower effective charge on the nucleus, therefore, they react more easily

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5
Q

Group 2 elements and water:

Magnesium and water

A

Mg (s) + H2O (g) —–> MgO (s) + H2 (g)

  • Heat/steam needed in order to react
  • Insoluble MgO formed.
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6
Q

Group 2 elements and water:

Cs/Sr/Ba and water

A

X (s) + 2H2O (l) ——-> X(OH)2 + H2 (g)

  • React with cold water
  • Basic metal hydroxide formed

Nb: Solubility of group 2 oxides increases down group, so state symbol varies

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7
Q

Reaction of Mg with oxygen

A

2Mg (s) + O2 (g) ——-> 2MgO (s)

Bright white flame

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8
Q

Reaction of Ca with oxygen

A

2Ca (s) + O2 (g) ——–> 2CaO (s)

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9
Q

Reaction of Sr with oxygen

A

2Sr (s) + O2 (g) ———> 2SrO (s)

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10
Q

Reaction of Ba with oxygen

A

2Ba (s) + O2 (g) ———> 2BaO (s)

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11
Q

Reaction of Mg with chlorine

A

Mg (s) + Cl2 (g) ———-> MgCl2 (s)

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12
Q

Reaction of Ca with chlorine

A

Ca (s) + Cl2 (g) ———-> CaCl2 (s)

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13
Q

Reaction of Sr with chlorine

A

Sr (s) + Cl2 (g) ———-> SrCl2 (s)

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14
Q

Reaction of Ba with chlorine

A

Ba (s) + Cl2 (g) ———-> BaCl2 (s)

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15
Q

Trend in solubility of group 2 hydroxides?

A

The solubility of group 2 INCREASES as you go down the group

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16
Q

Trend in solubility of group 2 hydroxides?

A

The solubility of group 2 hydroxides INCREASES as you go down the group

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17
Q

Trend in solubilty of group 2 sulfates

A

The solubility of group 2 sulfates DECREASES as you go down the group

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18
Q

Trend in solubility of group 2 sulfates

A

The solubility of group 2 sulfates DECREASES as you go down the group

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19
Q

Trend in solubility of group 2 carbonates

A

Group 2 carbonates are INSOLUBLE

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20
Q

Tests for group 2 salts

A

-Add Na2CO3 (aq) ——> White precipitate for ALL

-Add Na2SO4 (aq) ——–> MgSO4 = no ppt
BaSO4 = Thick ppt

-Add Na2OH (aq) ———> Mg(OH)2 = white ppt
Ba(OH)2 = No ppt

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21
Q

Thermal decomposition:

A

The use of heat to break down a reactant into multiple products

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22
Q

Thermal decomposition of carbonates

A

The positive ion causes heterolytic fission of the C—O- bond

The greater the charge density of the positive ion, the more readily this occurs

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23
Q

Thermal decomposition of Group 1 carbonates

A

Li2CO3 (s) ——-> Li2O (s) + CO2 (g)
Only Lithium carbonate (LiCO3) decomposes

Charge density in the other group 1 carbonates too low, and decomposition does not occur

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24
Q

Thermal decomposition of Group 2 carbonates

A

Thermal stability of group 2 carbonates INCREASES as you go down the group.

ie. they become more difficult to decompose as charge density DECREASES.

Therefore, the carbonate ion is less likely to be POLARISED.

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25
Test for sulfate ions
Ba2+ ions test for sulfate ions and sulfate ions test for Ba2+
26
Thermal decomposition of Group 1 nitrates
Lithium: 4LiNO3 (s) ---------> 2LiO (s) + 4NO2 (g) + O2 (g) Rest of group 1 nitrates: 2XNO3 (s) -----------> 2XNO3 (s) + O2 (g)
27
Thermal decomposition of Group 2 nitrates
2X(NO3)2 (s) --------> 2XO (s) + 4NO2 (g) + O2 (g)
28
NO2 (nitrate) observation
Brown gas
29
Trend in thermal decomposition of Group 2 nitrates
Thermal stability of group 2 nitrates INCREASES down the group ie. they become more difficult to decompose as charge density DECREASES. Therefore, the nitrate ion is less likely to be POLARISED.
30
How do we test the stability of carbonates?
One is to heat a known mass of carbonate in a side arm boiling tube and pass the gas produced through lime water. Time for the first permanent cloudiness to appear in the limewater.
31
How do we test the stability of nitrates?
Measure length of time it takes until a specific amount of NO2 is produced. NO2 is a brown gas that can easily be observed, but is toxic so must be done in a fume cupboard
32
How to carry out a flame test?
1. Use a nichrome wire 2. Sterilise the wire by dipping in concentrated hydrochloric acid and then heating in Bunsen flame 3. Make sure the sample powdered or grinded 4. Dip wire in solid and put in Bunsen flame and observe flame
33
Group 1 flame test colours:
``` Li - red Na - Yellow/orange K - Lilac Rb - Deep red Cs - Violet ```
34
Group 2 flame test colours:
Mg - No colour Ca - Orange/red Sr - Red Ba - Apple green
35
Explanation of the flame test colours
The heat causes the electron to get excited and be promoted to higher energy levels in the atoms As they fall back down their ground state, they emit excess energy in the form of an electromagnetic wave The further they fall, the higher the frequency emitted Different frequencies = different colours
36
Why does magnesium show no colour in a flame test
The frequency emitted by Mg may not fall in the visible light part of the spectrum
37
Reaction of group 2 oxides with water
They are basic metal oxides, and react readily with water Same equation for all, but magnesium hydroxide is solid, whereas rest are aqueous Mg (s) + H20 (l) -------> Mg(OH)2 (s) X (s) + H20 (l) -------> X(OH)2 (AQ)
38
Reaction of group 2 oxides with dilute acids
- Neutralisation reaction - Forms basic salt and water MO (s) + HCl (l) -------> MCl2 (aq) + H20 (l) MO (s) + H2SO4 (l) ---------> MSO4 + H20 (l)
39
Why is the Mg(OH)2 formed from the reaction between MgO and H20 only PH9 but the other hydroxides formed are PH12?
Mg(OH)2 is not as alkaline as it is only slightly soluble in water, so fewer OH- (aq) ions in solution
40
Note on group 2 sulfates
State symbol of MSO4 can be (s) or (aq). Solubility of group 2 sulfates DECREASES down the group
41
Reaction of group 2 hydroxides and acid
-They neutralise acids M(OH)2 + 2HCl (l) --------> MCl2 (aq) + 2H20 (l)
42
Trend in melting/boiling points of the group 7 elements
Melting/boiling points INCREASE down the group Halogens exist as non polar diatomic molecules Weak induced dipole forces exists between the molecules (these are broken when melted or boiled) Induced dipole forces become stronger as you go down the group as Mr increases. This is because more electrons are involved in the induced dipoles
43
Trend in electronegativity of the group 7 elements
Electronegativity DECREASES down the group Fluorine is the most electronegative as it has the greatest effective charge on the nucleus due to low shielding This increases its ability to attract a bonding pair of electrons
44
Testing for halide ions
1. Acidified silver nitrate | 2. Aqeuous ammonia
45
Why is the silver nitrate acidified?
Nitric acid is added to test solution first to remove (neutralise) any CO3^2- or OH- impurities present CO3^2- / OH- interfere with test because: Ag2CO3 -white ppt AgOH - brown ppt
46
Results after adding acidified silver nitrate: | Fluoride ions
Ag+ (aq) + F- (aq) ------> AgF(aq) | No ppt
47
Results after adding acidified silver nitrate: | Chloride ions
Ag+ (aq) + Cl- (aq) ------> AgCl (s) White ppt
48
Results after adding acidified silver nitrate: | Bromide ions
Ag+ (aq) + Br- (aq) ------> AgBr (s) | Cream ppt
49
Results after adding acidified silver nitrate: | Iodide ions
Ag+ (aq) + I- (aq) ------> AgI (s) | Pale yellow ppt
50
Results after adding aqueous ammonia: | Chloride ions
AgCl (s) dissolves in DILUTE NH3 (aq)
51
Results after adding aqueous ammonia: | Bromide ions
AgBr (s) dissolves in CONC NH3 (aq)
52
Results after adding aqueous ammonia: | Iodide ions
AgI (s) will NOT dissolve
53
Reaction of chlorine and water
Water reacts with chlorine to form HCl and chloric acid Cl2 + H20--------> HCl + HClO It is a disproportionation reaction as chlorine is oxidised from 0 in Cl2 to +1 in HClO and reduced from 0 in Cl2 to -1 in HCl HClO is antibacterial (oxidising agent), hence addition of chlorine to swimming pools and in water treatment
54
Reaction of chlorine and water in the presence of UV light
In the presence of UV light, chlorine and water do not produce chloric acid 2Cl2 + 2H20 ------> 2HCl + O2 Occurs in the presence of UV light, so outdoor pools need chlorinating more often
55
Reaction of chlorine and COLD DILUTE sodium hydroxide solution to form bleach
Chlorine reacts with COLD DILUTE sodium hydroxide solution to form sodium chloride, sodium chlorate (1) and water Cl2 + 2NaOH --------> NaCl + NaClO + H20 Chlorine is oxidised from 0 in Cl2 to +1 in NaClO and reduced to -1 in NaCl ClO- ions are oxidising agents and the active ingredient in bleach
56
Reaction of chlorine and HOT CONC sodium hydroxide solution to form bleach
Chlorine reacts with HOT CONC sodium hydroxide solution to form sodium chloride, sodium chlorate (5) and water 3Cl2 + 6NaOH --------> 5NaCl + NaClO3 + 3H20 Chlorine is oxidised from 0 in Cl2 to +5 NaClO3 and reduced to -1 in 5NaCl
57
What are halogens?
Halogens are oxidising agents The oxidising power DECREASEs down the group, with fluorine being the strongest oxidising agent and iodine the weakest This is because as you go down, the effective nuclear charge decreases due to the increase in shielding
58
What are halides?
Halides are reducing agents The reducing power INCREASES down a group with fluorine being the weakest reducing agent and iodine the strongest This is because as you go down, the effective nuclear charge decreases due to the increase in shielding
59
Displacement
redox reaction between a halogen and a halide A stronger oxidising agent displaces a weaker oxidising agent
60
Observation when chlorine is displaced
Pale green
61
Observation when bromine is displaced
Brown
62
Observation when iodine is displaced
Orange
63
Test for sulfate ions
Acidified barium solution. Produces barium sulfate which is a thick white ppt
64
Testing for group 1 ions
ALL are soluble
65
Testing for group 2 nitrate ions
All are soluble
66
Testing for group 2 hydroxide ions
Insoluble at top, soluble at bottom
67
Testing for group 2 sulfate ions
Soluble at top, insoluble at bottom
68
Testing for group 2 halide ions
All are soluble
69
Testing for group 2 carbonate ions
All insoluble white ppts
70
Reaction between Ag+ and OH- ions
Brown ppt | AgOH(s)
71
Reaction between Ag+ and S04^2- ions
White ppt | Ag2SO4
72
Reaction between Ag+ and CO3^2- ions
White ppt | Ag2CO3
73
Reaction between Ag+ and NO3- ions
Soluble
74
Reaction of halide ions and concentrated sulfuric acid: | Fluoride ions
NaF + H2SO4 --------> No reaction | No redox
75
Reaction of halide ions and concentrated sulfuric acid: | Chloride ions
NaCl + H2SO4 -------->HCl + NaHSO4 Acid/ base reaction No redox HCl = steamy fumes
76
Reaction of halide ions and concentrated sulfuric acid: | Bromide ions
NaBr + H2SO4 --------> HBr + NaHSO4 2H+ + 2Br- + H2SO4 --------> Br2 + SO2 + 2H2O Redox - sulfur reduced from +6 to +4
77
Reaction of halide ions and concentrated sulfuric acid: | Iodide ions
NaI + H2SO4 --------> HI + NaHSO4 2H+ + I- + H2SO4 --------> I2 + SO2 + 2H20 6H+ + 6I- + H2SO4 --------> 3I2- + S + 4H20 8H+ + 8I- +H2SO4 --------> 4I2- + H2S + 4H20
78
Observations during reactions of sodium halides with conc sulfuric acid: Hydrogen halides
HCl, HBr, HI Steamy fumes
79
Observations during reactions of sodium halides with conc sulfuric acid: Bromine
Brown fumes
80
Observations during reactions of sodium halides with conc sulfuric acid: Iodine
Purple fumes
81
Observations during reactions of sodium halides with conc sulfuric acid: sulfur dioxide
colourless gas with choking smell
82
Observations during reactions of sodium halides with conc sulfuric acid: Sulfur
Yellow solid
83
Observations during reactions of sodium halides with conc sulfuric acid: Hydrogen sulphide
H2S pungent gas with rotten egg smell
84
Reactions of hydrogen halides with water
All readily dissolve in water Hx (g) + H2O (l) --------> H3O+ (aq) + X- (aq) Classed as strong acids as so they fully disassociate to form H+ (aq). This increases the concentration of hydrogen ions, so creates an acidic solution
85
Reactions of hydrogen halides with ammonia
All readily react with ammonia Hx (g) + NH3 (g) --------> NH4x (s) solid salt produced but presents as white smoke

chemistry (13 decks)

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