1
Q
Name the group 14 elements
A
Carbon - silicon - germanium - tin - lead - flerovium
2
Q
Discuss abundancy of carbon
A
- Carbon is 17th most abundant element on Earth
2. It is also found as CO2 in air (0.03%)
3
Q
Discuss availability of carbon
A
- It is available in the elemental state as Diamond, Graphite and Coal
- It is available in combined state as metal carbonates, hydrocarbons and CO2
4
Q
Discuss isotopes of carbon
A
Carbon(12), Carbon(13) and Carbon(14)
5
Q
Which is the radioactive isotope of carbon? Mention half life
A
Carbon(14) is radioactive in nature
It has a half life of 5770 years and is used for radiocarbon dating
6
Q
Discuss occurrence of Silicon
A
- Silicon is second most abundant element on Earth’s crust
2. It exists in nature as silicates and silica
7
Q
Discuss occurrence of other metals
A
- Germanium occurs in traces
- Tin occurs as Cassiterite
- Lead occurs as Galena
- Flerovium is synthetically produced radioactive element
8
Q
Cassiterite
A
SnO2
9
Q
Galena
A
PbS
10
Q
Atomic number of Fl
A
114
11
Q
Mass of Fl
A
289 g/mol
12
Q
Electronic configuration
A
ns2np2
13
Q
Discuss covalent radius trend
A
From C to Si, there is a notable increase due to increase in number of shells
From Si to Pb, only a small increase is seen due to presence of completely filled d and f orbitals
14
Q
Discuss ionization enthalpy trend
A
- It is higher than group 13 elements
2. It decreases as we go down the group
15
Q
What is the exception in IE trend
A
There is a small decrease from Si > Ge > Sn (as expected) but there is an increase from Sn < Pb because of poor shielding effect of the d and f orbitals and increase in atomic size
16
Q
Discuss electronegativity trend
A
- Due to decrease in size, group 14 is more electronegative than group 13
- Electronegativity values of Si to Pb are almost the same
17
Q
Discuss physical properties of group 14 elements
A
- They are all solids
- C, Si are non-metals
- Ge is a metalloid
- Sn, Pb are soft metals with low MP
18
Q
Discuss all oxidation states
A
- They show +4 and +2 OS
2. Compounds with +4 are generally more covalent because sum of four IEs is quite high
19
Q
Discuss variation in oxidation states
A
- C, Si are very stable in +4 OS
- Ge forms stable compounds in both +4 and +2 (more +4 than +2)
- Sn is a good reducing agent in +2, forms compounds using both OS
- Pb is a good oxidizing agent in +4 and compounds in +2 are stable
- C can also show negative OS
20
Q
Why is one OS more stable than the other down the group
A
+2 is more stable because as we go down the group, ns electrons get more and more resistant towards participation because of shielding effect
21
Q
Do group 14 elements act as Lewis acids/bases? Why/why not?
A
They have 8 electrons and are hence electron precise elements and do not accept or donate an electron.
However, hydrolyzed compounds of Si, Ge, Sn and Pb accept electron pairs because of availability of d and f orbitals
22
Q
What kind of oxides are formed
A
Elements in this group form monoxides MO and dioxides MO2
23
Q
What is the general rule for acidity of oxides
A
Oxides in higher OS are more acidic than the ones in lower states
24
Q
Comment on acidity of group 14 oxides
A
- CO2, SiO2, GeO2 are all acidic
- SnO2 and PbO2 are amphoteric
- CO is neutral
- GeO is predominantly acidic
- SnO and PbO are amphoteric
25
Discuss reactivity with water
1. C, Si and Ge are unaffected by water
2. Sn decomposes water to release SnO2 and H2 gas
3. Pb does not react with water due to protective oxide layer formation
26
What kind of halides are formed
MX2 (ionic) and MX4 (covalent)
27
Discuss features of MX2
1. They are ionic
2. Their stability increases down the group
3. They are sp hybridized and linear in shape
4. Pb and Sn form MX2
28
Discuss features of MX4
1. They are covalent
2. Their stability decreases down the group
3. They are sp3 hybridized and tetrahedral in shape
4. C, Si, Ge form these
29
Why does PbI4 not exist?
Because when the first Pb-I bond is formed, not enough energy is released to unpair 6s2 electrons and send them to a higher energy level to have 4 unpaired electrons for 4 iodine atoms
30
Discuss halide solubility
1. Except CCl4, all halides are hydrolyzed because central atom can accommodate the lone pair of electrons from oxygen atom of water molecule
31
Discuss anomalies in carbon
1. Carbon has a maximum covalence of 4 unlike the other elements (absence of d orbitals)
2. Unique ability to show p(pi)-p(pi) bonds with itself and other atoms of similar size
3. Catenation - links with other carbon atoms to form chains and rings because the C-C bond is very strong
32
Why do heavier elements not show p(pi)-p(pi) bonds?
Because their atomic orbitals are too large and diffuse to have effective overlapping
33
Diamond
1. Crystalline lattice
2. Each C is sp3 hybridized and bonded to 3 other carbons in a tetrahedral way
3. This structure continues in space to create a rigid three dimensional structure
4. Extended covalent bonds are hard to break and hence diamond is the hardest substance on Earth
34
Diamond is covalent but still has high MP. Why?
Because of its extended directional covalent bonding system, the bonds are extremely difficult to break. Hence, MP is quite high
35
C-C bond length in diamond
154 pm
36
Graphite
1. Has layered structure
2. Each layer consists of planar hexagonal rings with C-C bonds.
3. Each C is sp 2 hybridized with 3 sigma bonds and 1 pi bond
4. The electrons are delocalized over the whole structure which makes graphite a good conductor
37
Why is graphite soft and slippery?
Because the layers of graphite can cleave easily
38
Distance between layers in graphite
340 pm
39
C-C bond length
141.5 pm
40
Fullerenes
1. Made by heating graphite in an electric arc in presence of inert gases like He or Ar
2. The sooty material formed by condensation consists of mainly C(60) molecules with a small amount of C(70) and traces of fullerenes going up to 350
41
Discuss structure of buckminsterfullerene
Buckminsterfullerene is the fullerene made of C60
1. Contains 20 6-membered rings and 12 5-membered rings
2. A 6 ring can be fused with a 6 or a 5 ring but a 5 ring can only be fused with a 6 ring
3. All carbons are sp2 hybridized with 3 sigma bonds and the remaining electron delocalized
4. Has 60 vertices
5. Contains both single and double bonds
6. Also called Bucky balls for short
42
Why is Buckminsterfullerene aromatic?
Because of presence of delocalized electrons
43
C-C and C=C bond length in BMF?
143.5 and 138.3 pm
44
Which is thermodynamically most stable allotrope of carbon?
Graphite
45
How is carbon black obtained?
By burning hydrocarbons in limited air
46
How is charcoal/coke obtained?
By heating wood or coal at high temperatures in absence of air
47
How much is 1 carat
200 mg
48
How is CO produced
1. Direct oxidation of C in limited supply of oxygen
2C + O2 = 2CO
2. Industrially, it is prepared by dehydration of formic acid using conc H2SO4 at 373 K
HCOOH + heat + H2SO4 = CO + H2O
3. Commercially it is produced by passing steam over hot coke
C + H2O = CO + H2
4. If air is used instead of steam also, CO can be prepared
2C + O2 + N2 = 2CO + N2
49
Water gas
Also called synthesis/syn gas
| CO + H2
50
Producer gas
CO + N2
51
Physical Properties and structure of CO
1. Colorless, odorless, tasteless gas
2. Almost water insoluble
3. CO has one sigma and two pi bonds
4. There is a lone pair on both carbon and oxygen
52
Chemical Properties of CO
1. Powerful reducing agent and is used to extract some metals out of their metal oxide ores
2. The lone pair on the C acts as a donor and results in the formation of metal carbonyls
53
Why is CO poisonous
Because CO tends to form a complex with hemoglobin which is more stable than the oxygen-hemoglobin complex. So, hemoglobin will not bind to oxygen and carry it around the body anymore, slowly causing death
54
How is CO2 prepared
```
1. By heating carbon in excess of air
C + O2(excess) = CO2
2. Industrially, by reacting HCl with CaCO3
2HCl + CaCO3 = CaCl2 + H2O + CO2
3. Commercially, by heating limestone
```
55
Physical properties and structure of CO2
1. Colorless, odorless, tasteless gas
2. Low solubility in water
3. sp hybridized linear molecule
4. Has 2 sigma and 2 pi bonds
5. Is involved in resonance
6. 0 dipole moment
56
CO2 + water = ?
H2CO3 - carbonic acid which dissociates in two steps to give (CO3)2-
57
Uses of H2CO3
The H2CO3/HCO3- buffer system helps maintain the pH of blood at around 7.26 - 7.42
58
Photosynthesis
Process by which plants take in CO2 and water to produce for themselves and humans, releasing oxygen in the process
6CO2 + 12H2O + hv + chlorophyll = C6H12O6 + 6O2 + 6H2O
59
Greenhouse effect
The effect of temperature rise due to excess CO2 in the atmosphere due to combustion of fossil fuels, decomposition of limestone, etc.
60
Dry ice
Formed when liquified CO2 is allowed to expand quickly
| Used to store ice creams and frozen food
61
What is CO2 used for
1. It does not support combustion and is hence used in fire extinguishers
2. Gaseous CO2 is used in soft drinks
3. It is also used to manufacture urea
62
Silica
SiO2
63
Name some crystalline forms of silica
Quartz, tridymite, cristoballite
64
Structure of silica
1. Covalent, 3D network solid
2. Each Si atom is bound to 4 oxygen atoms and each oxygen atom is bound to 2 Si atoms
3. Lots of mini tetrahedrons
4. The entire crystal may be considered as a giant molecule with eight member rings are formed with alternate Si and O2 atoms
65
Chemical properties of silica
1. Almost non-reactive because of high Si-O bond enthalpy
2. It is attacked by HF and NaOH
HF + SiO2 = SiF4 + H2O
NaOH + SiO2 = Na2SiO3 + H2O
66
Kieselghur
An amorphous form of silica used in filtration plants
67
Silicones
1. Organosilicon polymers
| 2. -(R2SiO)- is the repeating unit
68
Manufacture of silicones
Hydrolysis of alkyl or aryl substituted silicon chlorides RnSiCl(4-n)
69
Physical properties of silicones
1. Water repelling because they are surrounded by non-polar alkyl groups
2. High thermal stability
3. High dielectric strength
4. Resistant to oxidation and chemicals
70
Silicates
Minerals with basic structural unit - (SiO4)4-
| Examples - feldspar, zeolite, mica, asbestos
71
Structure of silicates
Each Si atom is bound to four oxygen atoms in a tetrahedron fashion
In silicates, either the discrete unit is itself present or a number of such units are joined together by 1/2/3/4 oxygen atoms per silicate units
They can eventually form chains, rings, 3D structures
72
Man made silicates
Glass, cement
73
Zeolites
When aluminum replaces some of the Si atoms in the 3D network, an overall -ve charge is acquired which is balanced by Na+ or K+ thereby producing feldspars and zeolites
74
Uses of zeolite
1. Catalyst in petrochemical industries for cracking of hydrocarbons and isomerization
2. ZSM-5 (a zeolite) converts alcohol directly to gasoline
3. Hydrated zeolites are used as ion exchangers to soften "hard" water
P Block
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