info@urfaculty.com

www.urfaculty.com

Govt. Job/ Sarkari Naukri, NEET, CAT, Bank Exam & Study materials

Wednesday, 22 February 2017

The P-Block Elements - IV


GROUP 16 ELEMENTS

Oxidation states:
  • They show -2, +2, +4, +6 oxidation states.
  • Oxygen does not show +6 oxidation state due to absence of d – orbitals.
  • Po does not show +6 oxidation state due to inert pair effect.
  • The stability of -2 oxidation state decreases down the group due to increase in atomic size and decrease in electronegativity.
  • Oxygen shows -2 oxidation state in general except in OFand O2F2
  • Thus, the stability of +6 oxidation state decreases and +4 oxidation state increases due to inert pair effect.
Ionisation enthalpy:
  • Ionisation enthalpy of elements of group 16 is lower than group 15 due to half-filled p-orbitals in group 15 which is more stable.
  • However, ionization enthalpy decreases down the group.
Electron gain enthalpy:
  • Oxygen has less negative electron gain enthalpy than S because of small size of O.
  • From S to Po electron gain enthalpy becomes less negative to Po because of increase in atomic size.
Melting and boiling point:
  • It increases with increase in atomic number.
  • Oxygen has much lower melting and boiling points than sulphur because oxygen is diatomic (O2) and sulphur is octatomic (S8).
Reactivity with hydrogen:
  • All group 16 elements form hydrides.
  • They possess bent shape.
  • Bond angle: H2O [373K] > H2S [213K] < H2Se [232K] < H2Te [269K]
Acidic nature:

H2O < H2S < H2Se < H2Te

This is because the H-E bond length increases down the group. Therefore, the bond dissociation enthalpy decreases down the group.
Thermal stability:

H2O < H2S < H2Se < H2Te < H2Po

This is because the H-E bond length increases down the group. Therefore, the bond dissociation enthalpy decreases down the group.
Reducing character:

H2O < H2S < H2Se < H2Te < H2Po

This is because the H-E bond length increases down the group. Therefore, the bond dissociation enthalpy decreases down the group.
Reactivity with oxygen: EO2 and EO3
  • Reducing character of dioxides decreases down the group because oxygen has a
  • strong positive field which attracts the hydroxyl group and removal of H+ becomes easy.
  • Acidity also decreases down the group.
  • SOis a gas where as SeO2 is solid. This is because SeO2 has a chain polymeric structure whereas SO2 forms discrete units.
Reactivity with halogens: EX2, EX4 and EX6
  • The stability of halides decreases in the order F- > Cl- > Br- > I-.
  • This is because E-X bond length increases with increase in size.
  • Among hexa halides, fluorides are the most stable because of steric reasons.
  • Dihalides are sp3 hybridised and so, are tetrahedral in shape.
  • Hexafluorides are only stable halides which are gaseous and have sp3d2 hybridisation and octahedral structure.
  • H2O is a liquid while H2S is a gas. This is because strong hydrogen bonding is present in water. This is due to small size and high electronegativity of O.
Oxygen:
Preparation:
Oxides:
The compounds of oxygen and other elements are called oxides.
Types of oxides:
Acidic oxides: Non- metallic oxides are usually acidic in nature.
Basic oxides: Metallic oxides are mostly basic in nature. Basic oxides dissolve in water forming bases e.g.,
Amphoteric oxides: They show characteristics of both acidic as well as basic oxides.
Neutral oxides: These oxides are neither acidic nor basic. Example: CO, NO and N2O
Ozone:
  • Preparation:
  • It is prepared by passing silent electric discharge through pure and dry oxygen 10 – 15 % oxygen is converted to ozone.
  • Structure of Ozone:
  • Ozone has angular structure. Both O = O bonds are of equal bond length due to resonance.
Sulphur:
  • Sulphur exhibits allotropy:
  • Yellow Rhombic ( a - sulphur)
  • Monoclinic ( b  - sulphur)
  • At 369 K both forms are stable. It is called transition temperature.
  • Both of them have Smolecules.
  • he ring is puckered and has a crown shape.
  • Another allotrope of sulphur – cyclo S6 ring adopts a chair form.
  • S2 is formed at high temperature ( ∼1000 K).
  • It is paramagnetic because of 2 unpaired electrons present in anti bonding p * orbitals like O2.
Sulphuric acid:

Preparation:

By contact process
Exothermic reaction and therefore low temperature and high pressure are favourable.
It is dibasic acid or diprotic acid.
It is a strong dehydrating agent.
It is a moderately strong oxidizing agent.

Click here to view complete Chemistry Free Study Materials and Notes for NEET Preparation

Click here to view complete Physics Free Study Materials and Notes for NEET Preparation

Click here to view complete Biology Free Study Materials and Notes for NEET Preparation

Click here to take NEET online practice tests by UrFaculty.com

No comments:
Write comments

Hey, we've just updated our test package. Check'it out here - https://goo.gl/r7FuPT
Join Youth Apps