Class 12 Chemistry P Block Elements Physical properties of group 16

Physical properties of group 16

  1. The electronic configuration for them are : ns2 np4
  • Oxygen (O)  [He]2s2,2p4
  • Sulphur (S) [Ne]3s2,3p4
  • Selenium (Se) [Ar]3d104s24p4
  • Tellurium(Te) [Kr]4d10,5s2,5p4
  • Polonium (Po) [Xe]4f14,5d10,6s2,6p4

 

  1. Atomic size: It increases down the group as every time a new shell is added as we move down. If we compare size of group 16 elements with group 15 then we see that group 16 is smaller due to increased nuclear charge.
  2. Ionization energy: If we compare ionization energy of group 16 and group 15 we see, that group 16 has lower energy than group 15 because of half filled stable electronic configuration of group 15 i.e. ns2np3.

As we move down the group, the ionization energy decreases because the size increases down the group.

  1. Electro negativity: The group 16 elements are more electro negative than group 15 because of small size of group 16 elements. This group has second highest electro negativity in whole periodic table.
  • Oxygen is second most electronegative in periodic table.
  • Down the group electro negativity decreases as size increases.
  1. Oxidation states: They generally show -2 oxidation state.
  • For oxygen: Common oxidation state is -2 but oxygen also show +2 oxidation state like in case of OF2 and in O2F2 the oxidation state is +1. The oxidation state of oxygen is in +ve because oxygen is less electronegative than fluorine.
  • For sulphur: The oxidation state shown is +2, +4, +6 (because of vacant d orbital). Like in SO2 the oxidation state of sulphur is +4 and in sulphuric acid the oxidation state is +6 and in H2S it is -2.
  • Down the group the vacant d orbital are present therefore they all can show +2, +4, +6 oxidation states.

Anomalous behavior of oxygen:

  • It has smallest size in its family.
  • It has highest ionization energy.
  • No vacant d orbital is present in it.
  • It is highly electronegative in its family.
  1. Electron gain enthalpy

Along period it is more negative because of attraction towards electron because of increased nuclear charge.

Down the group electron gain enthalpy keeps on becoming less negative because nuclear charge decreases and size increases.

The trend that was expected

  • O>S>Se>Te (wrong trend)
  • O<S>Se>Te (right trend)
  • Please note that oxygen has less electron gain enthalpy than sulphur because due to small size of oxygen the incoming electron suffers repulsion therefore electron gain enthalpy is less negative as compared to sulphur.

This whole group is called chalcogens as they are ore forming.

For example:

  • Al –bauxite ore
  • Pb-galena
  • Hg-cinnabar ore
  • Zn-zinc blende and many more.

Elemental state of oxygen and sulphur

Oxygen exists as diatomic gas, whereas sulphur exists as S8 in solid form in a puckered ring like structure as shown below:

 Class_12_P_Block_Group_16_Sulphur_Structure

 

Sulphur (crown-like structure)

  •  In case of oxygen pπ-pπ bonding takes place but in sulphur no such bonding takes place .That is the reason oxygen exist as gas and sulphur exist as solid.

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