Chapter 8: Reactivity trends Flashcards
(109 cards)
1
Q
name of group 2 elements:
A
- alkaline earth metals
- name comes from alkaline properties of metal hydroxides
2
Q
reactivity and natural elements of group 2:
A
elements are reactive metals and do not occur in elemental form naturally
- On earth they are found in stable compounds e.g calcium carbonate CaCO3
3
Q
what subshell are the 2 outer electrons in for group 2?
A
s sub-shell
4
Q
what is the most common type of reaction in group 2?
A
redox reactions
- each metal atom is oxidised,losing two electrons to form 2+ ion with the electron configuration of a noble gas
5
Q
oxidation of Ca example:
A
Ca → Ca2+ + 2e-
Ca is oxidised
6
Q
what happens to the two electrons lost in group 2 reaction?
A
another species will gain 2 electrons and be reduced
- group 2 element is a reducing agent as it has reduced another species
7
Q
Be atom configuration:
A
[He] 2s^2
8
Q
Be2+ ion configuration:
A
[He]
9
Q
Mg atom configuration:
A
[Ne] 3s2
10
Q
Mg2+ ion configuration
A
[Ne]
11
Q
Ca atom configuration
A
[Ar] 4s2
12
Q
Ca2+ ion configuration
A
[Ar]
13
Q
Sr atom configuration:
A
[Kr] 5s2
14
Q
Sr2+ ion configuration:
A
[Kr]
15
Q
Ba atom configuration:
A
[Xe] 6s2
16
Q
Ba2+ ion configuration:
A
[Xe]
17
Q
Ra atom configuration:
A
[Rn] 7s2
18
Q
Ra2+ ion configuration:
A
[Rn]
19
Q
what do group 2 and oxygen form?
A
metal oxide
- with general formula MO, made up of M2+ and O2- ions
20
Q
what happens when Magnesium reacts with Oxygen?
A
Mg burns with white light and forms magnesium oxide
21
Q
Formula of Mg and O2:
A
2Mg (s) + O2 (g) → 2MgO (s)
- oxidation and reeducation happens at the same time
22
Q
what does group 2 and water form?
A
alkaline hydroxide
- general formula M(OH)2 and hydrogen gas
23
Q
how fast does water and Mg react?
A
very slowly but becomes more vigorous further down the group - reactivity increases dow. the group
24
Q
hydrogen in group 2 reaction with water:
A
not all hydrogen atoms are reduced
25
what type of reaction do metals and acids make?
redox reaction
26
equation for metal + acid
metal + acid → salt + hydrogen
- all group 2 reacts like this
27
reactivity down group 2:
increases down the group
28
why does reactivity increase down group 2?
atoms of group 2 elements lose electrons to form +2 ions.
- the formation of +2 ions from gaseous atoms requires the input of two ionisation energies
29
first ionisation energy equation:
M (g) → M+ (g) + e-
30
second ionisation energy equation:
M+ (g) → M2+ (g) + e-
31
what happens to ionisation energies down group 2?
decrease down the group
- the attraction between the nucleus and the outer electrons decreases as the atomic radius and shielding increases
32
what makes up most of the energy input of group 2?
the first and second ionisation energies
- total energy input from ionisation energies to for, 2+ ions decreases down the group.
- group 2 elements become more reactive and stronger reducing agents down the group
33
what do oxides of group 2 react with?
water
- release hydroxide ions (OH-)
- forming alkaline solutions of metal hydroxide
34
formula for group 2 oxide with water:
CaO (s) + H2O (l) → Ca2+ (aq) + 2OH- (aq)
35
group 2 hydroxides solubility in water:
slightly soluble in water
- when solution becomes saturated, any further metal and hydroxide ions will form a solid precipitate
36
formula for group 2 saturated:
Ca2+ (aq) + 2OH- (aq) → Ca (OH)2 (s)
37
solubility of hydroxides of group 2 in water:
increases down the group so solution will contain more OH- (aq) ions and are more alkaline
38
which solid is slightly soluble in water?
only Mg(OH)2 is slightly soluble in water
- the solution has a low OH- (aq) and a pH 10
39
which solid is much more soluble in water?
Ba(OH)2 is much more soluble
- solution has a greater OH- (aq) concentration and pH 13
40
experiment for solubility of hydroxide trends!
1 Add a spatula of each Group 2 oxide to water in a test tube.
2 Shake the mixture. On this scale, there is insufficient water to dissolve all of the metal hydroxide that forms. You will have a saturated solution of each metal hydroxide with some white solid undissolved at the bottom of the test-tube.
3 Measure the pH of each solution. The alkalinity will be seen to increase down the group.
41
what do the uses of oxides, hydroxides and carbonates depend on?
their basic properties and ability to neutralise acids
42
Group 2 compounds in agriculture:
Calcium hydroxide Ca(OH)2 is added to fields as lime by farmers to increase pH of acidic soils
- white lime powder on fields
43
formula for calcium hydroxide neutralising!
Ca (OH)2 (s) + 2H+ (aq) → Ca2+ (aq) + 2H2O (l)
44
group 2 compounds in medicine:
- often used as antacids for treating acid indigestion
- many indigestion tablets use magnesium and calcium carbonates as main ingredient
- milk of magnesia is a suspension of white magnesium hydroxide Mg (OH)2 in water. Mg is only slightly soluble in water
45
what is the main acid in the stomach?
HCl
46
neutralisation reactions with Mg (OH)2 and CaCO3:
Mg (OH)2 (s) + 2HCl → MgCl (aq) + 2H2O (l)
CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + H2O (l) + CO2 (g)
47
what group is the most reactive non metallic?
group 7
48
how does group 7 occur on earth?
as stable halide ions (Cl-, Br-, I-) dissolved in sea water or combined with sodium or potassium as solid deposits such as NaCl
49
how do halogens exist at room temperature?
diatomic molecules X2
- contains elements in all 3 physical states at RTP changing from gas to liquid to solid down the group
50
halogens in solid states:
form lattices with simple molecular structures
51
F2 at RTP
18 electrons
boiling point: -188
appearance: pale yellow gas
52
Cl2 at RTP:
number of electrons: 34
boiling point: -34
state: pale green gas
53
Br2 at RTP
number of electrons: 70
boiling point: 59°
state: red brown liquid
54
I2 at RTP:
number of electrons: 106
boiling point: 184°
state: shiny grey black solid
55
At2 at RTP:
number of electrons: 170
boiling point: 230°
state: never been seen
56
how many electrons are in outer s subshell of halogens?
two electrons in outer s subshell
- 5 in outer p subshell
s2p5
57
What is the most common type of reaction for halogens?
Redox reaction
- gains one electron to form a 1- halide with the electron configuration of the nearest noble gas
58
Redox reaction of Cl:
Cl2 + 2e- → 2Cl-
- chlorine is reduced
- another species loses electrons to halogen atoms. It is oxidised
59
What is an oxidising agent?
It oxidises another species
60
How can displacement reactions of halogens with halide ions be carried out?
On a tube scale
61
What do halogen-halide reactions show?
The reactivity of halogens decreases down the group
62
What is added in halogen-halide displacement reactions?
A solution of each halogen is added to aqueous solutions of other hallides
E.g Cl2 is added to two aqueous solutions containing Br- and I-
-
63
What happens if the halogen added is more reactive than the hallide present?
- a reaction takes place, halogen displaces a halide from solution
- solution changes colour
64
Colour of solutions of iodine and bromine in water:
- can appear similar orange-brown colour depending on conc
65
How can you tell apart solutions of iodine and bromine in water?
An organic non polar solvent e.g cyclohexane can be added to mixture and shaken
66
Results of cyclohexane:
Non polar halogens dissolve more readily in cyclohexane than in water.
- iodine is a deep violet
67
Results of Cl- with Br2:
No reaction
68
Results of Cl- with I2:
No reaction
69
Results of Br- with Br2 and formula
- orange colour from Br2 formation
Cl2 (aq) + 2Br- (aq) → 2Cl- (aq) + Br2 (aq)
70
Results for Br- with I2:
No reaction
71
Results of I- with Cl2 and formula:
- violet colour from I2 formation
Cl2 (aq) + 2I- (aq) → 2Cl- (aq) + I2 (aq)
72
Results of I- with Br2 and formula:
- Video colour from l2 formation
Br (aq) + 2I- (aq) → 2Br- (aq) + I2 (aq)
73
Equation for reaction of chlorine with bromide ions
Full equation: Cl2 (aq) + 2NaBr (aq) → 2NaCl (aq) + Br2 (aq)
Ionic equation: Cl2 (aq) + 2Br- (aq) → 2Cl- (aq) + Br2 (aq)
74
Oxidation and reduction from reaction of chlorine with bromide ions:
2Br in 2Br-
Each Br decreases by +1
Total increase = +2
2Cl in Cl2
Each Cl decreases by -1
Total decrease = -2
75
Colour of fluorine when reacted:
- pale yellow colour, reacting with almost any substance it comes in contact with
76
Why is astatine rare?
It is radioactive and decays rapidly,
- element has never been seen
- it is predicted to be the least reactive halogen
77
What happens to the electrons for halogens in redox reactions?
Halogens gains electrons
- down the group, the tendency to gain an electron decreases and halogens become less reactive
78
what are the most common type of reactions in halogens?
redox
- each halogen atom is reduced, gaining one electron and forms 1- halide ion with electron configuration to nearest noble gas
79
what happens to another species in a redox reaction with halogens?
loses electrons to halogen atoms (oxidised)
- the halogen is the oxidising agent as it oxidises another species
80
how can displacement reactions with halide ions be carried out?
on a test tube scale
- the results show that the reactivity of halogens decreases down the group
81
what do the results of a displacement reaction show?
that the reactivity of halogens decreases down the group
82
process for tube scale testing for halide ions:
- a solution of each halogen is added to aqueous solutions of other halides
83
what happens if a halogen added is more reactive than the halide present?
- a reaction takes place and the halogen displacing the halide from solution
- solution changes colour
84
how to tell apart solutions of iodine and water?
- they can appear a similar orange brown colour depending on conc
- so add organic non-polar solvent e.g cyclohexane and shake
85
results from adding non polar solvent:
non polar halogens dissolved more readily in cyclohexane than in water
86
halogen displacement reactions of Cl- (aq) and Br2 (aq)
no reaction
87
halogen displacement reactions of Br- (aq) and Cl2 (aq):
orange colour from Br2 formation
Cl (aq) + 2Br- (aq) →2Cl- (aq) + Br2 (aq)
88
halogen displacement reactions of l- (aq) and Cl2 (aq)
violet colour from I2 formation
Cl2 (aq) + 2I- (aq) → 2Cl- (aq) + I2 (aq)
89
halogen displacement reactions of Cl- (aq) and I2 (aq)
no reaction
90
halogen displacement reactions of Cl- (aq) and Br2 (aq)
no reaction
91
halogen displacement reactions of l- (aq) and Br2 (aq)
violet colour from I2 formation
Br2 (aq) +2I- (aq) → 2Br- (aq) + I2
92
halogen displacement reactions of Br- (aq) and I2 (aq)
no reaction
93
summary of results in halogen displacement reactions:
- chlorine has reacted with both Br- and I-
- bromine has reacted with I-
- iodine has not reacted at all
94
what colour is fluorine?
- pale yellow has reacting with almost any substance
95
why is astatine rare?
it is radioactive + decays rapidly
- element has never been seen
96
what happens to electrons of halogens in redox reactions?
- halogens react by gaining elevrrons
- down the group tendency to gain an electron decreases + halogens become less reactive
97
number of inner shells in group 7:
F2 - 1inner shell
Cl2 - 2 inner shells
Br2 - 3 inner shells
I2 - 4 inner shells
At2 - 5 inner shells
98
what is the strongest oxidising agent in halogens?
fluorine
- gains electrons from other species more readily than other halogens
- halogens become weaker oxidant agents down the group
99
what is disproportionation?
a redox reaction where the same element is oxidised and reduced
- e.g reaction of chlorine + water with cold and dilute sodium hydroxide
100
what is chlorine used in?
- water purification
- disinfectant for drinking water
- changed public health by reducing waterborne diseases by killing bacteria
101
what happens when small amounts of chlorine are added to water?
a disproportionatoom reaction
- one chlorine molecule has one atom oxidised and another chlorine molecule reduced
102
products of disproportionate reactions in chlorine:
two products are both acids (caloric (I) acid HClO and HCl)
103
how does chlorine kill bacteria?
- bacteria killed by caloric (I) acid and chlorate (I) ions ClO- rather than by chlorine
104
what can Chloric (I) acid be used at?
a weak bleach
- demonstrate by adding indicator to solution of chlorine and water
- indicator first turns red from presence of two acids
- colour then disappears as bleaching action of chliric (I) happens
105
why is reaction of chlorine with water limited?
low solubility of chlorine in water
- if water contains dissolved sodium hydroxide, much more chlorine dissolves + another disproportionation reaction happens
106
formula for chlorine with cold, dilute, aqueous sodium hydroxide:
Cl2 (aq) + 2NaOH (aq) → NaClO (aq) + NaCl (aq) + H2O (l)
- one Cl reduced, other oxidised in products
107
what does the solution of chlorine with sodium hydroxide contain?
large conc of chlorate (I) ClO- and ions from sodium chlorate (I) NaClO that is formed
108
what is chlorine with cold dilute aqueous sodium hydroxide used for?
household bleach
109
what is chlorine with cold dilute aqueous sodium hydroxide used for?
household bleach
