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Oxygen Family
Oxygen is the first member of the group VIA and sulfur is the second member of the group VIA. Other member of this group are selenium, tellurium and polonium.
However, oxides of mercury and silver decompose completely, to yield the respective metal and oxygen.
Fig: Dioxygen molecule
Group 16 of the periodic table consists of five elements viz. Oxygen(O), sulfur(S), selenium(Se) , Tellurium(Te) and polonium(Po). The common term for these elements is oxygen family after the name of first element. They are also known as chalogens because these elements are generally formed ores.
The general valence shell configuration of group-16 elements is ns2np4.
The general valence shell configuration of group-16 elements is ns2np4.
| Element |
Atomic number | Electronic configuration |
| O | 8 |
1s2 , 2s2, 2p4 |
| S | 16 | 1s2 , 2s2, 2p6, 3s2 , 3p4 |
| Se | 34 | 1s2 , 2s2, 2p4, 3s2 , 3p6, 3d10, 4s2 , 4p4 |
| Te | 52 | 1s2 , 2s2, 2p4, 3s2 , 3p6, 3d10, 4s2 , 4p6,4d10,5s2,5p4 |
| Po | 84 | 1s2,2s2,2p4,3s2,3p6,3d10,4s2,4p6,4d10,5s2,5p6,5d10,6s2,6p4 |
Group 16 also shows same trend of periodic properties like metallic character, ionization energy, electron gain enthalpy, atomic radii and electronegativity.
Metallic Character
Like other groups, group-16 elements are also show increment in metallic nature from top to bottom in group. So first two elements; oxygen & sulfur are non-metallic in nature, selenium and tellurium is metalloid and show character of both metal and non-metal. The last element of group i.e. polonium is metallic and radioactive with short life time.
Atomic & Ionic Radii
The atomic radii of group-16 are smaller than previous group-15 but greater than next group that is group-17. This is because from group -15 to 16, the nuclear charge increases which results in greater attraction of the electrons by the nucleus. Same concept follows from group 16 to 17. In a group from top to bottom, atomic radii increase due to increase in the number of electronic shells.
The ionic radii show same trend in group and period as atomic radii.
Ionization Energy
It’s the amount of energy required to remove electron from the valence shell of an isolated neutral atom. In periodic table, ionization energy increases from left to right in period and decreases from top to bottom in a group. It means group-16 elements must show more ionization energy value compared to group-15.
But elements of group-16 unexpectedly show less ionization energy than previous group despite their smaller atomic radii and high nuclear charge. This is because group-15 elements have ns2, np3 valence shell configuration, which is more symmetrical and stable than oxygen family due to half filled np3 orbital.
In a group from top to bottom, ionization energy value decreases due to lager atomic radii and shielding effect of inner electron which increases with increase the nuclear charge.
But elements of group-16 unexpectedly show less ionization energy than previous group despite their smaller atomic radii and high nuclear charge. This is because group-15 elements have ns2, np3 valence shell configuration, which is more symmetrical and stable than oxygen family due to half filled np3 orbital.
In a group from top to bottom, ionization energy value decreases due to lager atomic radii and shielding effect of inner electron which increases with increase the nuclear charge.
Electron Gain Enthalpy
Electron affinity is the amount of energy released during the addition of electron in the valence shell of an isolated neutral atom.
Group-16 elements have ns2, np4 valence shell configuration and required two electrons to reach at Nobel gas configuration (octet configuration). So these elements have high tendency to accept two electrons and form X2-.
Hence oxygen family elements have large negative electron gain enthalpy next only to the group-17. But in a group, oxygen shows least negative value compared to other element in same group due to small size.Group-16 elements have ns2, np4 valence shell configuration and required two electrons to reach at Nobel gas configuration (octet configuration). So these elements have high tendency to accept two electrons and form X2-.
Electronegativity
The tendency of an atom to attract bonding electrons is termed as electronegativity. As we move on left side of periodic table, electronegativity increases. Halogens are most electronegative elements.
The group-16 show high electronegativity than nitrogen family (group-15). Oxygen family elements are highly electronegative due to small size and need of two electrons to attain noble gas configuration.
As we move down in group, electronegativity decreases because of increment in atomic radii.
The group-16 show high electronegativity than nitrogen family (group-15). Oxygen family elements are highly electronegative due to small size and need of two electrons to attain noble gas configuration.
As we move down in group, electronegativity decreases because of increment in atomic radii.
Because of high electronegativity & small size, oxygen can form various compound with metal, non-metal and hydrogen. For example,
Apart from these compounds, oxygen can form various oxyanions like,
| Compounds with hydrogen |
Water(H2O), Hydrogen peroxide(H2O2) | |
| Compounds with sulfur | Sulfur dioxide(SO2), Sulfur trioxide(SO3) | |
| Compounds with carbon | Carbon dioxide(CO2), Carbon monoxide(CO) | |
| Compounds with nitrogen | Nitrous oxide(N2O) Nitric oxide(NO) Nitrogen dioxide(NO2) Di nitrogen trioxide(N2O3) Di nitrogen tetra oxide(N2O4) Di nitrogen pent oxide(N2O5) |
|
| Compounds with metal | Oxides | Magnesium oxide (MgO) |
| Peroxide | Barium peroxide (BaO2) | |
| Super oxide | Potassium super oxide (KO2) | |
Apart from these compounds, oxygen can form various oxyanions like,
| Oxyanion |
Name |
| NO2- | Nitrite |
| NO3- | Nitrate |
| N2O2- | Hypo-Nitrate |
| NO43- | Orthonitrate |
| SO42- | Sulfate |
| SO32- | Sulfhite |
| S2O32- | Thiosulfate |
| S2O42- | Dithionate |
| S2O82- | Peroxydisulfate |
| ClO- | HypoChlorite |
| ClO2- | Chlorite |
| ClO3- | Chlorate |
| ClO4- | Perchlorate |
- Oxygen gas or dioxygen molecule is a tasteless, colorless and odorless gas.
- Oxygen gas can exists in all three physical state- solid, liquid and gases. It’s is pale-blue color in liquid and solid state. In solid form it shows It has a cubic crystal structure.
- Oxygen gas is highly soluble on water. 1 molecule of O2 for every 2 molecules of N2 present in water, compared to an atmospheric ratio of approximately 1:4. The solubility of oxygen in water depends on temperature.
- Oxygen gas liquefies at 90 K and freeze at 55 K.
- There are three possible isotopes of oxygen; 8O16, 8O17, 8O18.
- Ozone (O3) is one of the allotrope of oxygen.
- Molecular orbital theory proves that dioxygen is paramagnetic in nature.
Fig: Dioxygen molecule
Dioxygen molecule forms through the covalent bond between both oxygen atoms. There is a double bond between both atoms with high bond dissociation energy (493.4 kj/mol). Hence the cleavage of bond requires a high amount of energy. That is the reason, the reactions of dioxygen requires initiation by external heating. But once reaction started, the heat liberated during reaction and hence reactions are exothermic in nature.
There are some chemical properties of dioxygen molecule.
There are some chemical properties of dioxygen molecule.
Reaction with Litmus Paper
Since dioxygen is neutral in nature, hence there is no change in color of litmus paper with dioxygen.
Combustion Reaction
Dioxygen acts as a supporter for combustion reaction but itself not combustible. All organic compounds like hydrocarbons burn in the presence of oxygen to give carbon dioxide gas and water vapour.
Reaction with Metals
dioxygen forms alkaline oxides with active metals. But less reactive metals like gold and platinum.
Active alkali metal & alkaline earth metal form oxides, peroxide & super oxide with dioxygen.
With other metals, dioxygen forms metal oxides.
Reaction with Non-metal
Just like reaction with metal, dioxygen reacts with non-metals also like hydrogen, carbon, sulfur and phosphorus & form oxides. Reaction occurs at high temperature or in electric discharge.
For example, dioxygen forms water with hydrogen and with solid carbon; it forms carbon monoxide or carbon dioxide. Similarly, with solid phosphorus, it forms tetraphorphorus heptoxide or tetraphorphorus decoxide. When dioxygen reacted with solid sulfur, sulfur dioxide gas forms.
Reaction with other Compounds
Dioxygen can react with different organic and inorganic compounds to form various products.
For example
With sulfur dioxide it form sulfur trioxide at 723 K temperature and 2 atm pressure in the presence of platinum of V2O5 as a catalyst. This reaction used to prepare sulfuric acid in contact process. Reaction is reversible and exothermic in nature.
In Decon’s process, dioxygen oxidized hydrochloric acid to form water and chlorine gas. Reaction talks place at 700 K temperature and in the presence of CuCl2 catalyst.
Electric discharge
Dioxygen forms ozone under the action of silent electric discharge.
Respiration
It’s a very important chemical property of dioxygen. It involves in respiration of all living bodies. Basically respiration is a combustion process of carbohydrates to produce carbon dioxide and water with a large amount of energy.
Since dioxygen is neutral in nature, hence there is no change in color of litmus paper with dioxygen.
Combustion Reaction
Dioxygen acts as a supporter for combustion reaction but itself not combustible. All organic compounds like hydrocarbons burn in the presence of oxygen to give carbon dioxide gas and water vapour.
Reaction with Metals
dioxygen forms alkaline oxides with active metals. But less reactive metals like gold and platinum.
Active alkali metal & alkaline earth metal form oxides, peroxide & super oxide with dioxygen.
4K + O2(g) → 2K2O
2K + O2(g) → K2O2
K + O2(g) → KO2
With other metals, dioxygen forms metal oxides.
2 Zn(s) + O2 (g) → 2 ZnO(s)
Reaction with Non-metal
Just like reaction with metal, dioxygen reacts with non-metals also like hydrogen, carbon, sulfur and phosphorus & form oxides. Reaction occurs at high temperature or in electric discharge.
For example, dioxygen forms water with hydrogen and with solid carbon; it forms carbon monoxide or carbon dioxide. Similarly, with solid phosphorus, it forms tetraphorphorus heptoxide or tetraphorphorus decoxide. When dioxygen reacted with solid sulfur, sulfur dioxide gas forms.
2 H2 (g) + O2(g) → 2 H2O(g)
C(s) + O2 (g) → CO(g) or CO2(g)
P4(s) + O2(g) → P4O6(g) or P4O10(g)
S8(s) + 8 O2 (g) → 8 SO2(g)
C(s) + O2 (g) → CO(g) or CO2(g)
P4(s) + O2(g) → P4O6(g) or P4O10(g)
S8(s) + 8 O2 (g) → 8 SO2(g)
Reaction with other Compounds
Dioxygen can react with different organic and inorganic compounds to form various products.
For example
With sulfur dioxide it form sulfur trioxide at 723 K temperature and 2 atm pressure in the presence of platinum of V2O5 as a catalyst. This reaction used to prepare sulfuric acid in contact process. Reaction is reversible and exothermic in nature.
723k,2atm
2SO2(g)+O2(g) $\rightleftharpoons$ 2SO3(g)
V205
With ammonia, dioxygen forms nitric oxide at 500K temperature and in the presence of platinum. Reaction is used in Ostwald process for the preparation of nitric acid.500K,Pt
4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g)
In Decon’s process, dioxygen oxidized hydrochloric acid to form water and chlorine gas. Reaction talks place at 700 K temperature and in the presence of CuCl2 catalyst.
700K , CuCl2
4HCl (g) + O2 (g) → 2H2O(g) + Cl2(g)
4HCl (g) + O2 (g) → 2H2O(g) + Cl2(g)
Electric discharge
Dioxygen forms ozone under the action of silent electric discharge.
3O2(g) → 2O3(g)
Respiration
It’s a very important chemical property of dioxygen. It involves in respiration of all living bodies. Basically respiration is a combustion process of carbohydrates to produce carbon dioxide and water with a large amount of energy.
C6H12O6 (aq) + 6 O2 (g) → 6 CO2 (g) + 6 H2O(l)
