1
Q
What is the general electronic configuration of p-block elements?
A
ns2 np1–6 (except helium)
2
Q
What trend is seen in oxidation states of heavier p-block elements?
A
Oxidation states two units less than group oxidation state become more stable down the group due to inert pair effect
3
Q
What is the inert pair effect?
A
Tendency of ns2 electrons to remain unshared in heavier p-block elements
4
Q
Where are non-metals and metalloids located in the periodic table?
A
They exist only in the p-block
5
Q
Why are compounds between highly reactive metals and non-metals generally ionic?
A
Because electronegativity difference is large
6
Q
What is the nature of non-metal oxides?
A
They are acidic or neutral
7
Q
What is the nature of metal oxides?
A
They are basic
8
Q
Why does the first p-block element differ from others in the group?
A
Because of small size and absence of d-orbitals
9
Q
What is the maximum covalence of boron?
A
Four
10
Q
Why is maximum covalence of boron limited to four?
A
Because boron lacks d-orbitals
11
Q
Which p-block elements can exceed covalence of four?
A
Elements with d-orbitals like Al and heavier members
12
Q
Which group elements can form p-pi p-pi multiple bonds with themselves?
A
First members such as carbon
13
Q
Why do heavier elements not form p-pi p-pi bonds?
A
Their orbitals are large and diffuse causing poor overlap
14
Q
How does aluminium compare with boron?
A
Al is a metal but shows many similarities to boron
15
Q
Borax and Kernite
A
Borax Na2B4O7·10H2O and Kernite Na2B4O7·4H2O
16
Q
What are the two isotopes of boron?
A
B-10 and B-11
17
Q
Which boron isotope is more abundant?
A
B-11 (81 percent)
18
Q
Which is the most abundant elements in Earth’s crust?
A
O
Si
Aluminium
19
Q
Bauxite and Cryolite
A
Bauxite Al2O3·2H2O and Cryolite Na3AlF6
20
Q
Why does boron have a high melting point?
A
Due to strong crystalline lattice
21
Q
What is the physical nature of other group-13 members?
A
Soft metals with low melting point and high electrical conductivity
22
Q
Which group-13 metal has an unusually low melting point?
A
Gallium
23
Q
Why is gallium useful for temperature measurement?
A
It is liquid over wide temperature range and has high boiling point
24
Q
Why does boron not form B3+ ions?
A
Its first three ionisation enthalpies are very high
25
Why can aluminium form Al3+ ions?
Sum of first three ionisation enthalpies is much lower
26
What happens to stability of +1 oxidation state down group-13?
It increases for heavier elements
27
How does Lewis acidity change down group-13?
Lewis acidity decreases down the group
28
Why is BCl3 a strong Lewis acid?
It is electron deficient and accepts lone pair from donors
29
Write the reaction of BCl3 with ammonia
BCl3 + NH3 → BCl3·NH3
Planar Tetrahedral
Sp2 Sp3
30
Why is aluminium more electropositive than thallium?
Because Al forms Al3+ ions easily
31
Is crystalline boron reactive?
Crystalline boron is unreactive
32
Why is aluminium resistant to corrosion?
It forms a protective oxide layer
33
What happens when amorphous boron and aluminium are heated in air?
They form B2O3 and Al2O3
34
Write the reaction of group-13 elements with oxygen
4E + 3O2 → 2E2O3
35
Write the reaction of group-13 elements with nitrogen
2E + N2 → 2EN
36
Does boron react with acids or alkalis?
Boron does not react with acids and alkalis
37
How does aluminium react with mineral acids?
amphoteric 2Al + 6HCl → 2Al3+ + 6Cl− + 3H2
38
Why does concentrated nitric acid make aluminium passive?
It forms protective oxide layer
39
Write reaction of aluminium with aqueous alkali
2Al + 2NaOH + 6H2O → 2Na+ + [Al(OH)4]− + 3H2
40
What species forms when trichlorides hydrolyse hybd?
"[M(OH)4]− tetrahedral" sp3
41
What is the hybridisation of M in [M(OH)4]−?
sp3 hybridisation
42
What ion is formed when aluminium chloride dissolves in acidified water?
[Al(H2O)6]3+
43
What is the hybridisation of Al in [Al(H2O)6]3+?
sp3d2
44
What structural change gives stability to AlCl3?
It forms a dimer Al2Cl6
45
How do group-13 elements react with halogens?except what
2E + 3X2 → 2EX3 except TLI3
46
Why do white fumes appear around anhydrous AlCl3 bottle?
It is hydrolysed by moisture releasing HCl gas
47
Why are group-13 trihalides hydrolysed?
They are covalent and electron deficient
48
In G13 trichloride tribromide and iodides of all these elements being covalent in nature are hydrolysed in water to form ____ except _ element doesn't show this
[M(OH)4]− and [M(H2O)6]3+.... boron does not show
49
Why are monomeric trihalides strong Lewis acids?
They are electron deficient
50
Write the reaction of BF3 with ammonia
BF3 + NH3 → BF3·NH3
51
Why is maximum covalence of boron four?
Absence of d orbitals
52
Why can Al and heavier elements expand covalence beyond four?
Because d orbitals are available
53
How does AlCl3 achieve stability in solid state?
By dimerisation to Al2Cl6
54
What is orthoboric acid used for?
It is used as a mild antiseptic
55
What is the electrical conductivity of aluminium compared to copper?
On weight basis aluminium has twice conductivity of copper
56
Where are aluminium alloys widely used?
Packaging
57
Why is aluminium use reduced in domestic purposes?
Because of toxic nature of its compounds
58
Why is boron used in bullet proof vests?
Because boron fibres are strong and lightweight
59
Why is B-__ isotope useful in nuclear industry?
It absorbs neutrons and is used in control rods 10
60
What are borax and boric acid used to manufacture?
Heat resistant glass such as Pyrex and glass wool
61
What is borax used as in metallurgy?
A flux for soldering metals
62
Cassiterite Galena
Cassiterite SnO2 and Galena PbS
63
Where are ultrapure silicon and germanium used?
To make transistors and semiconductor devices
64
How do melting and boiling points of group-14 compare to group-13?
They are higher in group-14
65
Can carbon show negative oxidation states?
Yes carbon can show negative oxidation states
66
Nature of compounds in +4 oxidation state of group-14?
Generally covalent
67
Which oxidation state becomes more stable in heavier group-14 elements?
+2 oxidation state
68
Which tin oxidation state acts as reducing agent?
Sn2+
69
Which lead oxidation state is more stable?
+2 oxidation state
70
Which lead oxidation state is a strong oxidising agent?
+4 oxidation state compounds
71
What is valency satisfaction in CCl4?
Carbon has octet satisfied and is electron precise
72
Can carbon exceed covalence four?
No carbon cannot exceed covalence four
73
Why can Si Ge Sn Pb exceed covalence four?
Presence of d orbitals allows expansion
74
Why do heavier group-14 halides hydrolyse?
Central atom accepts lone pair in d orbitals
75
Which silicon oxide is stable only at high temperature?
SiO
76
How does acidity vary with oxidation state in oxides?
Higher oxidation state oxides are more acidic
77
How do carbon silicon and germanium react with water?
They are not affected by water
78
What happens when tin reacts with steam?
Sn + 2H2O → SnO2 + 2H2
79
Why is lead unaffected by water?
A protective oxide layer forms
80
What formulas do group-14 halides show?
MX2 and MX4
81
Which group-14 element does not react directly with halogens?
Carbon
82
Nature of most MX4 halides?
Covalent
83
Most of the MX4 halides are covalent except
SnF4 and PbF4 which are ionic
84
Which MX4 of group 14 does not exist? And why
PbI4..., Pb-I bond does not release enough energy to unpair 6s2 electrons
85
Which elements form MX2 halides?
Ge to Pb
86
Which is more stable in Sn halides SnCl2 or SnCl4?
SnCl2 is more stable
87
Which is more stable in Pb halides PbX2 or PbX4?
PbX2 is more stable
88
Which tetrachloride is resistant to hydrolysis?
CCl4
89
Why are other tetrachlorides hydrolysed?
Central atom accepts lone pair into d orbitals
90
Explain hydrolysis of SiCl4
SiCl4 + 4H2O → Si(OH)4 + 4HCl
91
Why is carbon unique in bonding?
It forms p-pi p-pi multiple bonds and catenation
92
Why do heavier elements not form pπ pπ bonds?
Their orbitals are large and diffuse
93
What is catenation?
Ability of atoms to form chains with themselves
94
What is the order of catenation ability?
C > Si > Ge ≈ Sn
95
Does lead show catenation?
Lead does not show catenation
96
bond enthalpy C-C Si-Si Ge-Ge Sn-Sn?
C-C >Si-Si> Ge-Ge >Sn-Sn
97
What property of carbon leads to allotropy?
Catenation and multiple bonding
98
Name two crystalline allotropes of carbon.
Diamond and graphite
99
What third allotropic family of carbon exists?
Fullerenes
100
Describe bonding in diamond
Each carbon is sp3 hybridised and bonded tetrahedrally forming 3D network
101
Why is diamond very hard?
Strong covalent network throughout lattice
102
Why does diamond have high melting point?
Strong covalent network requires high energy to break
103
Give one use of diamond
Abrasive and cutting tools
104
Describe bonding in graphite
Each carbon is sp2 hybridised forming hexagonal layers
105
How are graphite layers held together?
By weak van der Waals forces
106
Why is graphite slippery?
Layers slide easily due to weak forces
107
Why does graphite conduct electricity?
Delocalised electrons are mobile along layers
108
Where is graphite used as lubricant?
In high temperature machinery where oil cannot be used
109
How are fullerenes prepared?
By heating graphite in electric arc in inert gas
110
What does soot preparation contain?
Mainly C60 with C70 and traces of higher fullerenes
111
Why are fullerenes called pure carbon forms?
They have smooth structure without dangling bonds
112
What is shape of C60 molecule?
Soccer ball like structure called Buckminsterfullerene
113
How many rings does C60 contain?
Twenty six-membered rings and twelve five-membered rings
114
What hybridisation exists in fullerenes?
sp2 hybridisation
115
What type of bonding exists in fullerenes?
Delocalised bonding over structure
116
What are spherical fullerenes called?
Bucky balls
117
Which allotrope of carbon is thermodynamically most stable?
Graphite
118
What is standard enthalpy of formation of graphite?
Zero
119
Arrange graphite diamond and fullerene in increasing H form
G
120
How is carbon black obtained?
By burning hydrocarbons in limited supply of air
121
How is charcoal obtained?
By heating wood in absence of air
122
How is coke obtained?
By heating coal in absence of air
123
What reaction takes place when aluminium reacts with oxygen?
4Al + 3O2 → 2Al2O3
124
What happens when aluminium forms nitrides at high temperature?
2Al + N2 → 2AlN
125
What happens when aluminium reacts with halogens?
2Al + 3X2 → 2AlX3
126
Why are trihalides of boron electron deficient?
They have incomplete octet
127
Why does BCl3 form adducts?
To complete octet by accepting lone pair
128
Why are AlCl3 dimers bridged by chlorine atoms?
To complete coordination of aluminium
129
What is amphoteric nature of aluminium?
It reacts with both acids and bases
130
Write amphoteric reaction of aluminium with NaOH
2Al + 2NaOH + 6H2O → 2Na+ + [Al(OH)4]− + 3H2
131
Why is B2O3 formed on heating boron in air?
Because boron reacts with oxygen forming boron trioxide
132
What type of compounds are group-13 trihalides?
Mostly covalent
133
Why does Lewis acidity decrease down group-13?
Increase in size reduces electron deficiency
134
Why is aluminium chloride hydrolysed strongly?
Because Al3+ has high polarising power
135
Why does Ga show inert pair effect stronger than Al?
Greater nuclear charge and poor shielding by d-electrons
136
Why is Tl+ more stable than Tl3+?
Due to strong inert pair effect
137
What protects aluminium from further oxidation?
Tightly bound oxide film
138
What is structure of Al2Cl6?
Dimer with chlorine bridges
139
Why does boron form covalent compounds?
Its small size and high ionisation enthalpy prevent ionic bond formation
140
Why does Al form ionic compounds?
Lower ionisation enthalpy allows formation of Al3+ ions
141
Why does graphite cleave easily?
Weak van der Waals forces between layers
142
Why is diamond electrically non-conducting?
No free electrons in structure
143
Why can graphite act as electrode?
Presence of delocalised electrons allows conduction
144
Why are group-14 elements able to form chains?
Due to catenation property
145
Why does catenation decrease down the group?
Bond enthalpy decreases down the group
146
Why is PbX4 less stable than PbX2?
Inert pair effect stabilises +2 oxidation state
147
Why are SnCl4 and PbCl4 hydrolysed?
Because central atom uses d orbitals to accept electron pairs
148
Why is CCl4 not hydrolysed?
Carbon lacks d-orbitals to accept electron pair
149
Why does Sn show variable oxidation states?
Availability of both +2 and +4 states
150
Why is SiCl4 readily hydrolysed?
Silicon can expand coordination using d-orbitals
151
What property of carbon enables organic chemistry?
Catenation and ability to form multiple bonds
152
In which form does silicon occur in nature?
Silica and silicates
153
What is oxidation state of carbon in metal carbides?
Negative
154
Why are MX2 halides more ionic in heavier group-14 elements?
Because electronegativity decreases down the group
155
Which tin halide is stronger reducing agent?
SnCl2
156
Which lead halide acts as oxidising agent?
PbCl4
157
Why do group-13 halides form complexes?
Because they are electron deficient
158
What happens when AlCl3 is dissolved in water?
It forms hydrated ions and undergoes hydrolysis
159
Where are boron fibres used?
In aircraft and bulletproof materials
160
Why is boron used in nuclear control rods?
Because B-10 absorbs neutrons effectively
161
Why is graphite more stable than diamond thermodynamically?
Graphite has lower free energy
162
How many vertices does C60 have?
Sixty
163
fullerenes aromatic or non aromatic
Aromatic
164
Why is graphite used as dry lubricant?
Because layers slide easily and withstand high temperature
165
Why is diamond used in cutting tools?
Because of extreme hardness
166
Why is carbon black used in tyres?
As reinforcing agent in rubber
167
What is the coordination geometry of [M(OH)4]−?
Tetrahedral
168
What is the coordination geometry of [Al(H2O)6]3+?
Octahedral
169
Al2Cl6 structure?
Cl Cl Cl
\ / \ /
Al Al
/ \ / \
Cl Cl Cl
Terminal Al–Cl bond = 206 pm
Bridging Al–Cl bond = 221 pm
Cl–Al–Cl (terminal) = 118°
Cl–Al–Cl (bridge) = 101°
Al–Cl–Al (bridge angle) = 79°
Erwin Smith
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