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Group 16 Flashcards

1
Q

Group 16 elements

A

Oxygen - Sulphur - Selenium - Tellurium - Polonium

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2
Q

What are the group 16 elements also called? Why?

A

Chalcogens
Chalcogen in Greek means brass (whose main constituent is copper). It is used to show that most copper minerals contain oxygen or Sulphur

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3
Q

Occurrence of oxygen

A
  1. Oxygen is the most abundant element on Earth
  2. It forms 46.6% of the Earth’s crust
  3. It also constitutes 20.5% of dry air
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4
Q

Occurrence of sulphur

A
  1. Combined sulphur occurs mainly as sulphate
  2. Or even as sulphides - galena, zinc blende
  3. It is a part of organic materials like hair, wool, proteins, eggs
  4. It is found in traces as H2S in volcanoes
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5
Q

Gypsum

A

CaSO4.2H2O

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6
Q

Epsom salt

A

MgSO4.7H2O

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7
Q

Baryte

A

BaSO4

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8
Q

Copper pyrites

A

CuFeS2

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9
Q

Occurrence of Se, Te and Po

A
  1. Se and Te occurs as selenides and tellurides in sulphide ores
  2. Po is a decay product of uranium and thorium
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10
Q

Electronic configuration

A

ns2np4

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11
Q

Discuss atomic radii trend

A
  1. Atomic size increases as we go down the group due to subsequent increase increase in the number of shells
  2. Oxygen atom is exceptionally small though
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12
Q

Discuss ionization enthalpy trend

A
  1. Decreases down the group due to increase in size

2. Should be more than Group 15 but is actually less because group 15 has stable half filled configuration

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13
Q

Discuss electron gain enthalpy

A
  1. Oxygen has less negative value because of its compact nature but from sulphur to the end of the group, value keeps decreasing
    O > S < Se < Te < Po
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14
Q

Discuss electronegativity trend

A

Oxygen has highest electronegativity after fluorine

The electronegativity decreases down the group with increasing size i.e., metallic character increases down the group

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15
Q

Is Po radioactive? What is its half life

A

Po is a radioactive short lived element.

It has a half life of 13.8 days

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16
Q

Physical properties of group 15 elements

A
  1. They all show allotropy
  2. Their MP, BP increases with increasing size
  3. O, S are non-metals
  4. Se, Te are metalloids
  5. Po is a non-metal
17
Q

Why is there a large difference in BP/MP of oxygen and sulphur

A

Because of their atomicities

Oxygen exists as a diatomic molecule while sulphur exists as a polyatomic molecule (S8)

18
Q

Discuss oxidation state variation

A
  1. O tends to show -2 because of its high electronegativity except with OF2 where OS is +2
  2. Stability of -2 decreases down the group.
  3. +4 and +6 is more common in the other elements
  4. S, Se and Te tend to show +4 with oxygen and +6 with fluorine
  5. Stability of +4 increases down the group while +6 decreases due to inert pair effect
  6. Bonding in +4, +6 are covalent
19
Q

Anomalous behavior of oxygen

A
  1. Because of its small size and high electronegativity, it forms strong hydrogen bonds in H2O which is not seen in H2S
  2. Has a maximum covalence of four due to absence of d orbitals but in practice, covalence rarely exceeds two
20
Q

Discuss hydrides formed

A
  1. Of the form H2E
  2. Their acidic character increases down the group due to decrease in BDE of H-E bond
  3. Thermal stability also decreases down the group
  4. Except H2O, they are all good reducing agents and this reducing character increases down the group
21
Q

Discuss properties of EO2

A
  1. Their reducing character decreases down the group
  2. SO2 is a reducing agent while TeO2 is an oxidizing agent
  3. O3 and SO2 are gases while SeO2 is a solid
  4. They are all acidic in nature
22
Q

Discuss properties of EO3

A
  1. Not formed by oxygen

2. SO3, SeO3 and TeO3 are all acidic in nature

23
Q

What kind of halides are formed? How does stability vary

A
  1. EX2, EX4 and EX6 halides are formed
  2. The stability varies as:
    F- > Cl- > Br- > I-
24
Q

Discuss properties of EX6

A
  1. Only hexafluorides are stable
  2. They are octahedral
  3. They are gaseous in nature
  4. SF6 is particularly stable for steric reasons
25
Discuss properties of Ex4
1. SF4 is a gas, SeF4 is a liquid and TeF4 is a solid 2. They are all trigonal bipyramidal with one lone pair i.e., seesaw shape 3. sp3d hybridization
26
Discuss properties of EX2
1. Except with oxygen, dichlorides and dibromides are formed | 2. sp3 hybridization and tetrahedral shape
27
Discuss properties of EX
1. Monohalides dimerize 2. Examples - S2Cl2, S2F2 3. They disproportionate to give EX4 + E
28
How is O2 prepared
1. By heating oxygen containing salts like chlorates, permanganates, etc. 2KClO3 = 2KCL + 3O2 2. By thermal decomposition of oxides of metals low in the electrochemical series and higher oxides of some metals 2PbO2 = 2PbO + O2 3. Hydrogen Peroxide readily decomposes to give water and O2 2H2O2 = 2H2O + O2 4. On a large scale, it is prepared by electrolysis of water - hydrogen at the cathode and oxygen at the anode 5. Industrially, CO2 and water is removed from air. This air is then liquified and fractionally distilled to give N2 and O2
29
Physical properties of dioxygen
1. Colorless, odorless gas 2. Soluble in water - solubility is 3.08 cm3 which is just sufficient for marine life 3. It liquifies at 90 K and freezes at 55 K 4. Paramagnetic despite having even number of electrons
30
Discuss isotopes of dioxygen
O(16), O(17) and O(18) | O(18) is radioactive
31
Chemical properties of dioxygen
1. It reacts with all metals and non-metals except the noble gases and inert metals like Au, Ag, Pt. These combination reactions are highly exothermic which helps sustain the reaction but a good amount of energy has to also be supplied because BDE of O=O is quite high 4Al + 3O2 = 2Al2O3 2. Some compounds are also catalytically oxidized 2SO2 + O2 (presence of V2O5) = 2SO3
32
Uses of dioxygen
1. Respiration 2. Oxyacetylene welding 3. Thermite process 4. Extraction of metals 5. Rocket propellant 6. Combustion
33
How are oxides classified
1. Simple (MgO, Al2O3) and mixed (Pb3O4, Fe3O4) Mixed oxides decompose to give one or more simple oxides Fe3O4 = FeO + Fe2O3
34
How are simple oxides classified
1. Based on their acidic, basic or amphoteric nature
35
Comment on acidic oxides
1. Oxides which on dissolving in water produce an acid are called acidic oxides CO2 + H2O = H2CO3 (carbonic acid) 2. All non-metal oxides are acidic 3. Some metal oxides where the metal has high OS are also basic (Mn2O7, CrO3, V2O5)
36
Comment on basic oxides
1. Oxides which on dissolving in water produce a base are called basic oxides CaO + H2O = Ca(OH)2 2. All metal oxides are basic
37
Comment on amphoteric oxides
Oxides that show acidic and basic character are called amphoteric oxides Al2O3
38
Comment on neutral oxides
Oxides that are neither acids or bases are called neutral | CO, NO, N2O

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