Periodic Table Flashcards
1
Q
What are the factors affecting atomic radius?
A
- number of filled quantum shells
- nuclear charge
- shielding effect
2
Q
How does number of filled principal quantum shell affect atomic radius?
A
The greater the number of filled principal quantum shells, the further the valence electrons are from the nucleus, the larger the atomic radius
3
Q
How does nuclear charge affect atomic radius?
A
The greater the nuclear charge the stronger the electrostatic attraction the nucleus has on valence electrons
4
Q
What affects shielding effect?
A
The larger the number of filled inner principal quantum shells of electrons, the greater the shielding effect experienced by valence electrons
5
Q
What is the trend of atomic radius across a period?
A
- across a period, atomic radii of elements decrease gradually
- there is an increase in nuclear charge while shielding effect by inner principal quantum shells of electrons remains relatively constant, thus nuclear charge increases
6
Q
What is the trend of atomic radii down a group?
A
- down a group, atomic radii of elements increase gradually
- down the group, the number of filled principal quantum shells increases, the increase in nuclear charge is cancelled out by the increase in shielding effect by the inner principal quantum shell of electrons
7
Q
How do cationic radii compare with atomic radii and why?
A
- cationic radii is always smaller than atomic radii
- atoms lose electrons to form cations, thus cations formed usually have one less principal quantum shell of electrons
8
Q
How do anionic radii compare with atomic radii and why?
A
- anionic radii is always larger than atomic radii
- to form anions, electrons are added to the outermost principal quantum shell of atoms, as a result, there is greater electron-electron repulsion in the outermost principal quantum shell of anions formed
9
Q
What is the trend of ionic radii of isoelectronic ions with increasing atomic number?
A
- isoelectronic radii of isoelectronic ions decrease with increasing atomic number
- as atomic number increases, nuclear charge increases, ionic radii decreases
10
Q
What is the variation of electrical conductivities across period 3?
A
- electrical conductivities are high for Na, Mg and Al and increases from Na to Al
- Na, Mg and Al have giant metallic lattice structure
- number of delocalised valence electrons increases from Na to Al
- electrical conductivity drops sharply at Si
- Si has a giant covalent structure and is a semi conductor
- electrical conductivities drop to 0 at P₄ and remains at zero to Ar
- P₄ to Cl₂ have simple covalent structures and Ar has a monoatomic structure
- there are no mobile charge carriers to conduct electricity
11
Q
What is the variation of electrical conductivities across period 2?
A
- electrical conductivities are high for metals Li and Be and increases from Li to Be
* Li and Be has giant metallic lattice structure
* number of delocalised valence electrons increases from Li to Be - electrical conductivities drop sharply to zero at B and remains at 0 from B to Ne except for C (graphite)
* B and C (diamond) have giant covalent structures, N₂ to F₂ have simple covalent structures and Ne has a monoatomic structure
* no mobile charge carriers to conduct electricity
* C (graphite) has delocalised valence electrons along the layers to conduct electricity in the direction parallel to the layers
12
Q
What are the trends for melting point and ΔHfᵤₛ of period 3 elements?
A
- melting points of Na, Mg and Al are fairly high and increases from Na, Mg to Al
* Na, Mg and Al have giant metallic lattice structures
* a large amount of energy is required to overcome the strong electrostatic forces of attraction between metal cations and sea of delocalised mobile valence elctrons
* as number of delocalised valence elecrtons increases from Na to Al, strength of metallic bonds increases - melting point reaches a maximum at Si
* Si has a giant covalent structure with strong and extensive covalent bonds between Si atoms - melting point drops sharply to P and melting point remains low fro P to Ar
* phosphorous, sulfure and chlorine have simple covalent structures and Ar has a monoatomic structure
* a smaller amount of energy is required to overcome the weak id-id
* melting point of sulfur, phosphorous, chlorine, argon
* S₈, P₄, Cl₂
* number of electrons of S₈ > P₄ > Cl₂, strength of id-id S₈ > P₄ > Cl₂
13
Q
What are the trends for melting point and ΔHfᵤₛ of period 2 elements?
A
- melting point of Li and Be are fairly high and increases from Li to Be
* Li and Be have giant metallic lattice structures with strong electrostatic forces fo attraction between metal cations and sea of delocalised mobile valence electrons
* as number of delocalised mobile valence increases from Li to Be, strength of metallic bonds increases - melting point continues to increase from B and reaches a maximum at C
* B and C have giant covalent structures with strong covalent bonds between atoms - melting point drops sharply to N and remains low from N to Ne
* N, O and F have simple covalent structures while Ne have monoatomic structure, with weak id-id
* a small amount of energy is required to overcome the weak id-id
14
Q
What is enthalpy change of fusion, ΔHfᵤₛ?
A
Enthalpy change when 1 mole of substance changes from solid to liquid
15
Q
What is enthalpy change of vaporisation, ΔH(vap)?
A
enthalpy change when 1 mole of substance changes from liquid to gas
16
Q
What is the structure of Li?
A
Giant metallic lattice structure
17
Q
What is the structure of Be?
A
Giant metallic lattice structure
18
Q
What is the structure of Boron?
A
giant covalent
19
Q
What is the structure of C?
A
giant covalent
20
Q
What is the hybridisation for C atoms in diamond?
A
sp³ hybridised
21
Q
What is the hybridisation of C in graphite?
A
- sp2 hybridised
- 4th 2p electron of each carbon atom is delocalised along the layers
22
Q
What is the structure of nitrogen?
A
Simple covalent
23
Q
What is the structure of oxygen?
A
Simple covalent
24
Q
What is the structure of fluorine?
A
Simple covalent
25
What is the structure of Neon?
Monoatomic
26
What is the bonding of monoatomic structure?
Weak id-id interactions hold discrete atoms together
27
What chloride do Na form?
| What is the state?
NaCl (s)
28
What is the structure and bonding of NaCl?
* giant ionic lattice structure
* ionic bonds
29
What is the effect of adding NaCl to water and the approximate pH?
* dissolves to give a neutral solution
* pH = 7
30
What chloride do Mg form?
| What is the state?
MgCl₂ (s)
31
What is the structure and bonding of MgCl₂?
- giant ionic lattice structure
- ionic bonds
32
What is the effect of adding MgCl₂ to water and the pH?
* dissolves and undergoes partial hydrolysis to give a weakly acidic solution
* pH = 6.5
33
What chlorides do aluminium form?
| What is the state?
AlCl₃ (s)
34
What is the structure and bonding of AlCl₃?
* simple covalent structure
* intermolecular forces (id-id)
35
What is the melting point of AlCl₃?
It sublimes at 180°C due to weak intermolecular forces (id-id)
36
What is the effect of adding AlCl₃ to water and its resultant pH?
* dissolves and undergoes hydrolysis to give an acidic solution
* white fumes of HCl formed if amount of water used is small
* pH = 3
37
What chloride do Si form?
| What is the state?
SiCl₄ (l)
38
What is the structure and bonding of SiCl₄?
- simple covalent structure
- id-id
39
What is the effect of adding SiCl₄ into water and resultant pH?
* SiCl₄ dissolves and undergoes hydrolysis to give an acidic solution
* white fumes of HCl formed if amount of water used is small
* pH = 2
40
What chloride do phosphorous form?
| What is the state?
* PCl₅ (s)
* PCl₃ (l)
41
What is the structure and bonding of PCl₅ and PCl₃?
* simple covalent
* **PCl₅ id-id (non-polar)** [main one]
* PCl₃ pd-pd (polar)
42
What is the effect of adding PCl₅ in water and resultant pH?
* dissolves and undergoes hydrolysis to give an acidic solution
* white fumes of HCl formed if amount of water used is small
* pH = 2
43
What chloride do S form?
| What state?
S₂Cl₂ (l)
44
What is the structure and bonding of S₂Cl₂?
* simple covalent
* pd-pd (polar)
45
What is the effect of adding S₂Cl₂ to water?
* dissolves and undergoes hydrolysis to give an acidic solution
* white fumes of HCl formed if amount of water used is small
* pH = 2
46
What is the shape of aluminium chloride in gaseous state and what happens at high temperatures?
* dimers (Al₂Cl₆) in gaseous state due to formation of dative bonds
* At high temperatures, dimers dissociate into its monomers (AlCl₃)
47
What is the shape of Al₂Cl₆?
tetrahedral
48
What is the shape of AlCl₃?
Trigonal planar
49
What is the shape of S₂Cl₂?
bent
50
What can P exhibit?
* P exhibits multiple oxidation states
* PCl₅ exists because P can expand its octet by using its energetically accessible vacant 3d orbitals for bonding and accomodate more than 8 electrons in outershell
51
Why does S not form SCl₆?
Although it has energetically accessible vacant 3d orbitals, it does not form SCl₆ due to steric hindrance about central S atom
(a lot of repulsion because Cl is quite big)
52
What is hydration?
Process whereby water molecules interact with ions to form ion-dipole interactions
53
What is hydrolysis?
Reaction with water
54
What happens when NaCl(s) is added to water?
| equation
* NaCl (s) dissolves readily in water to form a neutral solution (pH = 7)
* only hydration and no hydrolysis occur as Na⁺ has low charge density and low polarising power
* NaCl (s) → Na⁺ (aq) + Cl⁻ (aq)
55
What happens when MgCl₂(s) is added in water?
* MgCl₂ readily dissolves in water to form a weakly acidic solution, pH = 6.5
* both hydration of ions and partial hydrolysis of Mg²⁺ occurs
* MgCl₂ (s) + 6H₂O (l) → [Mg(H₂O)₆]²⁺ (aq) + 2Cl⁻ (aq)
* [Mg(H₂O)₆]²⁺ (aq) + H₂O (l) ⇌ [Mg(H₂O)₅(OH)]⁺ (aq) + H₃O⁺ (aq)
56
What happens when AlCl₃(s) is added in water?
| equation, explain why
* AlCl₃(s) dissolves readily in water to form an acidic solution (pH = 3)
* Both hydration of ions and substantial hydrolysis of Al³⁺ occurs
* due to its high charge density, Al³⁺ is highly polarising and weakens O-H bonds in water molecules of the complex, causing OH bond to break and release hydrogen ions
* AlCl₃ (s) + 6H₂O (l) → [Al(H₂O)₆]³⁺ (aq) + 3Cl⁻ (aq)
* [Al(H₂O)₆]³⁺ (aq) + H₂O (l) ⇌ [Al(H₂O)₅(OH)]²⁺ (aq) + H₃O⁺ (aq)
57
What chlorides will be hydrated in water?
* ionic chlorides
* covalent chlorides with high ionic character like AlCl₃
58
When will a hydrated ion undergo hydrolysis and what happens to the resultant solution?
* if cation has high charge density, hydrated cations will undergo hydrolysis and solution is acidic
* otherwise solution is neutral
59
What is the extent of hydrolysis across a period 3?
* charge density of isoelectronic cations increses since charge increases and cationic radius decrease
* charge density of Na⁺ < Mg²⁺ < Al³⁺, thus extent of hydrolysis is Na⁺ < Mg²⁺ < Al³⁺
60
What happens if SiCl₄ (l) is added to water?
| equation
* SiCl₄ (l) dissolves in water to form a strongly acidic solution, pH = 2 and white solid SiO₂
* SiCl₄ undergoes hydrolysis in water, because Si in SiCl₄ has energetically accessible vacant 3d orbital for dative bonding with water molecules
SiCl₄ (l) + 2H₂O (l) → SiO₂ (s) + 4HCl (aq)
61
What happens if CCl₄ is added to water?
* CCl₄ does not reaction with water (no hydrolysis) since C atom has no energetically accessible vacant orbitals for dative bonding with water (vacant 3s, 3p, 3d orbitals are too high in energy)
62
What happens if PCl₅ and PCl₃ is added to water?
| equations
* they undergo hydrolysis in water to give strongly acidic solutions (pH = 2)
* P atom is able to use its energetically accessible vacant 3d orbitals for dative bonding with water molecules
* PCl₅ in limtied water: PCl₅ (s) + H₂O (l) → POCl₃ (l) + 2HCl (aq)
* PCl₅ in excess water: PCl₅ (s) + 4H₂O (l) → H₃PO₄ (aq) + 5HCl (aq)
63
What happens when S₂Cl₂ is added to water?
| equation
* S₂Cl₂(l) reacts slowly with water
* 2S₂Cl₂ (l) + 2H₂O (l) → 3S (s) + SO₂ (aq) + 4HCl (aq)
64
What happens when Cl₂ is added to water?
| equation
* Cl₂ (g) reacts with water to form an acidic solution
* Cl₂ (g) + H₂O (l) ⇌ HOCl (aq) + HCl (aq)
65
What oxide do Na form?
| With state symbol
Na₂O (s)
66
What is the structure and bonding of Na₂O (s)?
* giant ionic lattice structure
* ionic bonds
67
What is the melting point of Na₂O?
sublimes at 1275°C
68
What is the acid/base behaviour of Na₂O?
basic
68
What is the effect of adding Na₂O to water and resultant pH?
* reacts to form a strongly alkaline solution
* pH = 13
69
What oxides do Mg form?
| Include state symbols
MgO (s)
70
What is the structure and bonding of MgO?
* giant ionic lattice structure
* ionic bonds
71
What is the acid/base behaviour of MgO?
basic
72
What happens when MgO is added to water and the resulting pH?
* reacts to form a weakly alkaline solution
* pH = 8
73
What oxides do Al form?
| Include state symbols
Al₂O₃ (s)
74
What is the structure and bonding of Al₂O₃?
* giant ionic lattice structure
* ionic (with covalent character)
75
What is the acid/base behaviour of Al₂O₃?
amphoteric
76
What is the effect of adding Al₂O₃ to water and resultant pH?
* insoluble
* pH = 7
77
What is the oxide formed with Si?
| Include state symbols
SiO₂ (s)
78
What is the structure and bonding of SiO₂ (s)?
* giant covalent structure
* covalent
79
What is the acid/base behaviour of SiO₂ (s)?
acidic
80
What is the effect of adding water to SiO₂ (s) and resultant pH?
* insoluble
* pH = 7
81
What oxides do P form?
| Include state symbols
* **P₄O₁₀ (s)**
* P₄O₆ (s)
82
What is the structure and bonding of P₄O₁₀ (s)?
* simple covalent
* id-id (polar)
83
What is the melting point of P₄O₁₀ (s)?
sublimes at 300°C
84
What is the acid/base behaviour of P₄O₁₀ (s)?
Acidic
85
What is the effect of adding P₄O₁₀ (s) and P₄O₆ (s) into water and resultant pH?
* reacts to form an acidic solution
* pH = 2
86
What oxides do S form?
* **SO₃ (l)**
* SO₂ (g)
87
What is the structure and bonding of SO₃ (l)?
* simple covalent structure
* id-id (non-polar)
88
What is the structure and bonding of SO₂ (g)?
* simple covalent structure
* pd-pd (polar)
89
What is the acid/base behaviour of SO₃ (l) / SO₂ (g)?
acidic
90
What happens when SO₃ (l) / SO₂ (g) is added to water and resultant pH?
* reacts to form an acidic solution
* pH = 2
91
What oxides do Cl form?
| Include state symbols
* Cl₂O₇ (l)
* Cl₂O (g)
91
What is the structure and bonding of Cl₂O₇ (l) and Cl₂O (g)?
* simple covalent structure
* pd-pd (non-polar, bent shape)
92
What is the acid/base behaviour of Cl₂O₇ (l) and Cl₂O (g)?
acidic
93
What is the effect of adding Cl₂O₇ (l) and Cl₂O (g) in water and resultant pH?
* reacts to form an acidic solution
* pH = 2
94
What is the reaction and equation of Na₂O (s) with water?
* Na₂O (s) reacts vigorously with water to form NaOH (aq) which is strongly alkaline (pH = 13)
* Na₂O (s) + H₂O (l) → 2NaOH (aq)
95
How does Na₂O (s) react with acid/base and what's the equation?
* Na₂O (s) reacts with acid to form salt and water
* Na₂O (s) + 2H⁺ (aq) → 2Na⁺ (aq) + H₂O (l)
96
How does MgO react with water and what's the equation?
* MgO (s) reacts with water to form Mg(OH)₂ (s) which dissolves sparringly in water to give weakly alkaline (pH = 8) solution
* MgO (s) + H₂O (l) → Mg(OH)₂ (s)
* Mg(OH)₂ (s) ⇌ Mg²⁺ (aq) + OH⁻ (aq)
97
What is the reaction of MgO with acid/base and the equation?
* MgO (s) reacts with acid to form salt and water
* MgO (s) + 2H⁺ (aq) → Mg²⁺ (aq) + H₂O (l)
98
What is the reaction of Al₂O₃(s) with water and why?
* Al₂O₃(s) is insoluble in water due to large magnitude of lattice energy
* energy released during hydration of ions through the formation of ion-dipole interaction is insufficient to compensate for the strong electrostatic attraction between Al³⁺ and O²⁻ to break down the giant ionic lattice
* thus pH of water remains at 7
99
What is the reaction of Al₂O₃ with acid/base and the equations?
* Al₂O₃(s) reacts with both acid and alkali to form salt and water
* With acid: Al₂O₃(s) + 6H⁺ (aq) → 2Al³⁺ (aq) + 3H₂O (l)
* With base: Al₂O₃(s) + 2OH⁻ (aq) + 3H₂O (l) → 2[Al(OH)₄]⁻ (aq)
100
What is the reaction of SiO₂ (s) in water?
* SiO₂ insoluble in water as a large amount of energy is required to break the strong and extensive covalent bonds in giant covalent structure
* pH unaffected, pH = 7
101
What is the reaction of SiO₂ with acid/base and the equation?
* SiO₂ reacts with concentration alkali to form salt and water
* SiO₂ (s) + 2OH⁻ (aq) → SiO₃²⁻ (aq) + H₂O (l)
SiO₃²⁻: silicate
102
What is the reaction of P₄O₁₀ in water and equations?
* P₄O₁₀ reacts violently with water to give an acidic solution, pH = 2
* P₄O₁₀ (s) + 6H₂O (l) → 3H₃PO₄ (aq)
103
What is the reaction of P₄O₁₀ with acid/base and equation?
* react violently with alkali to form salt and water
* P₄O₁₀ (s) + 12OH⁻ (aq) → 4PO₄³⁻ (aq) + 6H₂O (l)
104
What is the reaction of SO₃ with water?
| equation
* SO₃(l) react with water to give acidic solutions (pH = 2)
* SO₃ (l) + H₂O(l) → H₂SO₄ (aq)
105
What is the reaction of SO₂ (g) with water?
| equation
* SO₂ (g) + H₂O (l) → H₂SO₃ (aq)
106
What is the reaction of SO₂ (g) with acid/alkali and the equation?
* SO₂ (g) react with alkali to form salt and water
* SO₂ (g) + 2OH⁻ (aq) → SO₃²⁻ (aq) + H₂O (l)
107
What is the reaction of SO₃ (l) with acid/alkali and the equation?
* SO₃ (l) react with alkali to form salt and water
* SO₃ (l) + 2OH⁻ (aq) → SO₄²⁻ (aq) + H₂O (l)
108
What is the reaction of Cl₂O and Cl₂O₇ with water?
| equations
* Cl₂O and Cl₂O₇ react with water to give acidic solutions (pH = 2)
* Cl₂O (g) + H₂O (l) → 2HClO (aq)
* Cl₂O₇ (l) + H₂O (l) → 2HClO₄ (aq)
109
What is the reaction of Cl₂O and Cl₂O₇ with acid/base?
| equations
* Cl₂O(g) and Cl₂O₇ (l) react with alkali to form salt and water
* Cl₂O(g) + 2OH⁻ (aq) → 2ClO⁻ (aq) + H₂O (l)
* Cl₂O₇ (l) + 2OH⁻ (aq) → 2ClO₄⁻ (aq) + H₂O (l)
110
What is the nature of NaOH and reaction with acid/base?
* base
* NaOH (s) + HCl (aq) → NaCl (aq) + H₂O (l)
111
What is the nature of Mg(OH)₂ and reaction with acid/base?
* basic
* Mg(OH)₂ (s) + 2HCl (aq) → MgCl₂ (aq) + 2H₂O (l)
112
What is the nature of Al(OH)₃ and reaction with acid/base?
* amphoteric
* Al(OH)₃ (s) + 3HCl (aq) → AlCl₃ (aq) + 3H₂O (l)
* Al(OH)₃ (s) + OH⁻ (aq) → [Al(OH)₄]⁻ (aq)
113
What element is separated from Group II elements?
* Be (because it has properties distinct from the rest)
* Ra is radioactive
114
What is the standard electrode potential of Group 2 elements and why?
* highly negative
* they are good reducing agents, thus they are readily oxidised
114
What happens when Group II carbonates are heated?
| equation
* thermally unstable and decompose to give metal oxide and carbon dioxide
* MCO₃ (s) → MO (s) + CO₂ (g)
114
What is the trend of standard electrode potential of Group II elements down the group?
* down the group
* atomic radii increses
* increse in nuclear charge is cancelled out by the increase in shiedling effect
* electrons are further from the nucleus and less attracted to the nucleus
* IE decreases, meaning its easier to lose electrons
* tendency to oxidise increases
* stronger reducing power
* standard electrode potential mroe negative down the group
115
What is the equation of thermal decomposition of Group II nitrates?
M(NO₃)₂ (s) → MO (s) + 2NO₂ (g) + 1/2O₂ (g)
116
What is the equation for thermal decomposition of Group II hydroxides?
M(OH)₂ (s) → MO (s) + H₂O (g)
117
Why do thermal decomposition of Group II nitrates, carbonates and hydroxides occur?
* metal cation polarises the electron cloud of the large NO₃⁻ / CO₃²⁻ / OH⁻ to such an extent that the covalent bonds in the anion are weakened
* these weakened bonds are readily broken when heat is applied
118
What is the trend of thermal stability of Group 2 carbonates/nitrates/hydroxides down the group?
* down the group, the radius of the metal cation, M²⁺ increases and its charge density decreases
* as a result the ability of M²⁺ to polarise the electron cloud of the large NO₃⁻ / CO₃²⁻ / OH⁻ anion decreases
* C-O bonds are weakened to a smaller extent
* thermal stability increases down the group
119
What is volatility and what does it depend on?
* tendency of a substance to vapourise
* depends on boiling point of substance
* higher boiling point, less voltaile
120
What is the trend of volatility of halogens down the group?
* down the group, number of electrons increases
* electron cloud of each molecule increases in size and become more polarisable
* more energy is required to overcome stronger id-id between halogen molecules
* increase in boiling point and decrease in volatility down the group
121
What is the trend of standard electrode potentials of halogens down the group?
* down the group
* atomic radii increases
* increase in nuclear charge is cancelled out by increase in shielding effect
* electron to be added is further away from nucleus and less attracted by it
* EA decreases, meaning it is harder to gain electrons to form negative halide ions
* tendency to reduce decreases
* oxidising power decreases
* standard electrode potential decreases
122
How can displacement reactions of halogen molecules determine the relative oxidising power?
Halogens of higher oxidising power will displace less reactive halide
123
What happens when Cl₂ added to Br⁻ and what does this mean?
* orange solution formed
* immiscible orange-red organic layer formed
* Cl₂ + 2Br⁻ → Br₂ + 2Cl⁻
Means oxidising power of Cl₂ > Br₂
124
What happens when Cl₂ added I⁻ and what does this mean?
* black ppt. formed in brown solution
* immiscible violet organic layer formed
* Cl₂ + 2I⁻ → I₂ + 2Cl⁻
Means oxidising power of Cl₂ > l₂
125
What happens when Br₂ added to Cl⁻ and what does this mean?
* no colour change
* Br₂ cannot oxidise Cl⁻
Means oxidising power of Cl₂ > Br₂
126
What happens when Br₂ added I⁻ and what does this mean?
* black ppt. formed in brown solution
* immiscible violet organic layer formed
* Br₂ + 2I⁻ → I₂ + 2Br⁻
Means oxidising power of Br₂ > I₂
127
What happens when l₂ added to Cl⁻ and what does this mean?
* no colour change
* I₂ is not able to oxidise Cl⁻
Means oxising power of Cl₂ > I₂
128
What happens when l₂ added to Br⁻ and what does this mean?
* no colour change
* I₂ is not able to oxidise Br⁻
Means oxidising power of Br₂ > I₂
129
What is the order of oxidising power of halogens?
Cl₂ > Br₂ > I₂
130
What happens when hydrogen halides are added to polar and non-polar solvents?
* hydrogen halides can dissolve in polar and non-polar solvents
* when dissolved in non-polar solvents, they retain their covalent character
* when dissolved in polar solvents, they dissociate to form strong acids
131
What is the trend of boiling point/volatility down the group for hydrogen halides?
* HF has exceptionally high boiling point/low volatility compared to other hydrogen halides
* hydrogen bonds between HF molecules require more energy to overcome
* Boiling point of hydrogen halides increases from HCl to HBr to HI (volatility decreases)
* number of electrons in the molecules increases, more energy is required to overcome stronger id-id
132
What happens when HF is heated?
Shows little tendency to decompose
133
What happens when HCl is heated?
Shows little tendency to decompose
134
What happens when HBr is heated?
| equations
* produces red brown bromine vapour on strong heating
* 2HBr (g) → H₂ (g) + Br₂ (g)
135
When happens when HI is heated?
* gives copious violet fumes of iodine when a red-hot steel needle is plunged into a jar of hydrogen iodide
* 2HI (g) → H₂ (g) + I₂ (g)
136
What happens to the thermal stability of hydrogen halides down the group?
* down the group
* size of halogen atoms increase
* valence orbitals become more diffused
* less effective overlap of orbitals between small H atom and larger halogen atom
* less energy is required to break the weaker H-X bond
* thermal stability of hydrogen halide decreases down the group
