Group Chemistry Notes - Chemistry

Chemistry: Group Chemistry Notes - Chemistry

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Points to be Remembered

1. Group 1:

  • Ionic Radii: As moving down a group the principal quantum no. increases, the distance between the nucleous and the outermost shell electron will also increase. Hence, the ionic radii will also, in general, increases down the group.
  • Ionization Energy: As the size increases from up to down, the force of attraction between the nucleous and the outermost shell electron will decrease Hence, the ionization energy will decrease down the group.
  • B.P./M.P.: Down the group the no. of the inner shell electrons increases. Hence, electronic repulsion will increase. Hence, the inter-molecular force decrease. Hence, the bp/mp will also decrease down the group.
  • Reducing Character: As the ionization energy of gr.1 elements decrease from Li to Cs, the ability of giving up of electrons will also increase down the group. Hence, reducing ability will also increase down the group.
    But, in terms of E°red value Li is strongest reducing agent. This is due to the smallest size of Li metal among the alkali metals.
  • Hydration Enthalpy: According to Fajan higher is the ionic potential of a cation greater will be the chance of hydration. Ionic potential is defined as: ϕ = Charge of cation/Size of cation. As the charge of all alkali metal ions are same and the size increase from up to bottom of the group, the ionic potential will decrease from Li+ to Cs+. Hence, the hydration energy will be decreased from Li+ to Cs+.
  • Oxidation State: The valence shell electronic configuration of alkali metals are ns1. Hence, by losing one electron it will attain the stable inert gas electronic configuration. Hence, the single oxidation state of gr. 1 metals are +1.
  • Flame Colouration: Alkali metals contains loose bound electrons. Hence, on heating electronic transition will occur. If the energy associated with electronic transition falls in the visible region then it will appear as colour. Na and K shows yellow and violet colour.
  • Reaction with Ammonia: When alkali metals are added to liquid ammonia then ammoniated cation and ammoniated electron are formed. Due to the formation of ammoniated cation and ammoniated electrons the solution become blue in colour. Due to the presence of ammoniated electron it shows conductance. Also. the solution exhibit paramagnetic property. But, as the solution made concentrated, the odd electron will combine with each other and hence, the paramagnitism will decrease.
  • Reaction with Oxygen: The order of size of alkali metal cations: Li+ < Na+ < K+ < Rb+ < Cs+. Hence, the order of ionic potential is: Li+ > ....> Cs+. The order of the negative charge density of the following three species are: O2- > O22- > O2-. Hence, highest positively charge dense Li+ will combine with highest negative charge dense O2- leading to the formation of lithium oxide. Then, moderate positive charge dense Na+ will combine with moderate negative charge dense O2-2 leading to the formation of sodium peroxide. Finally, all other less positive charge dense cations will combine with least negative charge dense species O2- leading to the formation of potassium, ..., cesium superoxide.

2. Group 2:

  • Ionic Radii: As moving down a group the principal quantum no. increases, the distance between the nucleous and the outermost shell electron will also increase. Hence, the ionic radii will also, in general, increases down the group.
  • Ionization Energy: As the size increases from up to down, the force of attraction between the nucleons and the outermost shell electron will decrease Hence, the ionization energy will decrease down the group. Due to the full-tilled valence shell electronic configuration, much more energy, compared to alkali metals, will require to remove the electron causing very high first ionization energy. But, in case of second ionization energy the l.E. value is relatively low as removal of second electron will help the species to attain more stable octet configuration.
  • B.P./JM.P.: Down the group the no. of the inner shell electrons increases. Hence, electronic repulsion will increase. Hence, the inter-molecular force decrease. Hence, the bp/mp will also decrease down the group. But, at the same time the molecular weight will also increases. Hence, bp/mp should also increase. Hence, on combing these two factors at first bp/mp will decrease then it will start to increase.
  • Reducing Character: As the ionization energy of gr. 2 elements decrease from Be to Ba, the ability of giving up of electrons will also increase down the group. Hence, reducing ability will also increase down the group.
  • Hydration Enthalpy: According to Fajan higher is the ionic potential of a cation greater will be the chance of hydration. Ionic potential is defined as : ϕ = Charge of cation/Size of cation. As the charge of all alkaline earth metal ions are same and the size increase from up to bottom of the group, the ionic potential will decrease from Be2+ to Ba2+. Hence, the hydration energy will be decreased down the group.
  • Oxidation State: The valence shell electronic configuration of alkaline earth metals are ns2. Hence, by losing two electrons these will attain the stable inert gas electronic configuration. Hence, the single oxidation state of gr. 2 metals are +2.
  • Flame Colouration: Alkaline metals contains loose bound electrons. Hence, on heating electronic transition will occur. If the energy associated with electronic transition falls in the visible region then it will appear as colour. Ca and Sr shows brick red and crimson red.
  • Reaction with Ammonia: When alkaline earth metals are added to liquid ammonia then ammoniated cation and ammoniated electron are formed. Due to the formation of ammoniated cation and ammoniated electrons the solution become blue in colour. Due to the presence of ammoniated electron it shows conductance. Also, the solution exhibit paramagnetic property. But, as the solution made concentrated, the odd electron will combine with each other and hence, the paramagnitism will decrease.

3. Group 13:

  • Ionic Radii: As we moving down a group, due to increase in principal quantum no. the distance between the nucleous and outermost shell electron will increase. Hence, ionic radii should increase steadily. But, due to scandide contraction (d-orbital contraction) and lanthanide contraction (f-orbital contraction) the increase in size in case of Ga and T1 are relatively low.
  • Ionization Energy: As the size decrease from up to down, the force of attraction between the nucleous and the outermost shell electron will also decrease Hence, the ionization energy will decrease down the group. But, due to scandide contraction (d-orbital contraction) and lanthanide contraction (f-orbital contraction) the increase in size in case of Ga and Tl are relatively low. Hence, in case of Ga and Tl ionization energy will increase compared to its previous one.
  • B.P./M.P.: Down the group the no. of the inner shell electrons increases. Hence, electronic repulsion will increase. Hence, the inter-molecular force decrease. Hence, the bp/mp will also decrease down the group. But, at the same time the molecular weight will also increases. Hence, bp/mp should also increase. Hence, on combing these two factors at first bp/mp will decrease then it will start to increase.
  • Hydration Enthalpy: According to Fajan higher is the ionic potential of a cation greater will be the chance of hydration. Ionic potential is defined as: ϕ = Charge of cation/Size of cation. As the charge of all gr. 13 metal ions are same and the size increase from up to bottom of the group, the ionic potential will decrease from B3+ to Tl3+. Hence, the hydration energy will be decreased down the group.
  • Oxidation State: The valence shell electronic configuration of gr. 13 metals are ns2np1. Hence, by losing three electrons these will attain the stable inert gas electronic configuration. Hence, the group oxidation state of gr.13 elements are +3. But, due to inert pair effect the most stable oxidation state of TI is two unit less than the group oxidation state of TI i.e. its most stable oxidation state is +1.
  • Halides of B: All the halides of B are monatomic. These are electron deficient. Hence, these will undergo pπ(X)-pπ(B) back bonding to remove its electron deficiency. Due to smaller size of B and F, this overlap will be most effective in BFand it will be least effective in BI3. Hence, availability of getting vacant p-orbital on B is highest in case of BI3 and lowest in case of BF3. Hence, the Lewis acidity order is : BF3 < ..... < BI3.
  • Halides of Al: AIX3 is also electron deficient. Hence, these will undergo dimerization. Hence, AlCl3 exist as dimer i.e. Al2Cl6.

4. Group 14:

  • Ionic Radii: As we moving down a group, due to increase in principal quantum no. the distance between the nucleous and outermost shell electron will increase. Hence, ionic radii should increase steadily. But, due to scandide contraction (d-orbital contraction) and lanthanide contraction (f-orbital contraction) the increase in size in case of Ge and Pb are relatively low.
  • Ionization Energy: As the size decrease from up to down, the force of attraction between the nucleous and the outermost shell electron will also decrease Hence, the ionization energy will decrease down the group. But, due to scandide contraction (d-orbital contraction) and lanthanide contraction (f-orbital contraction) the increase in size in case of Ge and Pb are relatively low. Hence, in case of Ge and Pb ionization energy will decrease to a little extent.
  • B.P./M.P.: Down the group the no. of the inner shell electrons increases. Hence, electronic repulsion will increase. Hence, the inter-molecular force decrease. Hence, the bp/mp will also decrease down the group. But, at the same time the molecular weight will also increases. Hence, bp/mp should also increase. Hence, on combing these two factors at first bp/mp will decrease then it will start to increase.
  • Hydration Enthalpy: According to Fajan higher is the ionic potential of a cation greater will be the chance of hydration. Ionic potential is defined as: ϕ = Charge of cation/Size of cation. As the charge of all gr. 14 metal ions are same and the size increase from up to bottom of the group, the ionic potential will decrease from C4+ to Pb4+. Hence, the hydration energy will be decreased down the group.
  • Oxidation State: The valence shell electronic configuration of gr. 14 metals are ns2np2. Hence, by losing four electrons these will attain the stable inert gas electronic configuration. Hence, the group oxidation state of gr. 14 elements are +4. Blit, due to inert pair effect the most stable oxidation state of Pb is two unit less than the group oxidation state of Pb i.e. its most stable oxidation state is +2.
  • Catenation: An element will show catenation property which is neither highly electronegative nor highly electropositive. Moreover, it should form M-M as well as M O bonds. These properties are fully satisfied by C. Hence, it shows catenation property uniquely. As the electropositivity increases down the group, the catenation property is decreases down the group.
  • Allotropy: The main three allotropic forms of carbons are diamond, graphite and fullerene.
  • I. Diamond: All the carbons in diamond are sp3+ hybridized. C-C bond length in diamond is 1.54 A0. Due to absence of free electrons, diamond is nonconductor. But, due to its 3-D structure diamond has very high mp.
  • II. Graphite: All the carbons in graphite are sp2 hybridized. One double bond undergo resonance with two C=C bonds. Hence, C-C bond order is 1.33. Due to the presence of free π-electrons it is conductor of heat and electricity. As the various layers are weakly attached with each other by van der Waal's force, graphites are slippery. Its mp is low.
  • III. Fullerene: It is the purest form of carbon. It contains pentagonal and hexagonal rings. The no. of pentagonal rings are 10 while the no. of hexagonal rings are : n/2 - 10, where n = no. of carbons in fullerene. In case of C60 and C70 the no. of hexagonal rings are 20 and 25 respectively.

5. Group 15:

  • Ionic Radii: As we moving down a group, due to increase in principal quantum no. the distance between the nucleous and outermost shell electron will increase. Hence, ionic radii should increase steadily. But, due to scandide contraction (d-orbital contraction) and lanthanide contraction (f-orbital contraction) the increase in size in case of As and Bi are relatively low.
  • Ionization Energy: As the size decrease from up to down, the force of attraction between the nucleous and the outermost shell electron will also decrease Hence, the ionization energy will decrease down the group. But, due to scandide contraction (d-orbital contraction) and lanthanide contraction (f-orbital contraction) the increase in size in case of As and Bi are relatively low. Hence, in case of As and Bi ionization energy will decrease to a little extent.
  • B.P./M.P.: Down the group, the molecular weight increases. Hence, bp/mp increases down the group.
  • Electronegativity: As the size increases down the group, electronegativity should decrease down the group. But, due to scandide contraction the electronegativity of As is somewhat larger than its previous one.
  • Oxidation State: The valence shell electronic configuration of gr.15 metals are ns2np3. Hence, by losing five electrons these will attain the stable inert gas electronic configuration. Hence, the group oxidation state of gr. 15 elements are +5. But, due to inert pair effect the most stable oxidation state of Bi is two unit less than the group oxidation state of Bi i.e. its most stable oxidation state is +3.
  • Catenation: An element will show catenation property which is neither highly electronegative nor highly electropositive. Moreover, it should form M-M as well as M-O bonds. As nitrogen is highly electronegative, it will show very little catenation property. Rather P shows better catenation property. Then, catenation property decrease down the group.

6. Group 16:

  • Ionic Radii: As we moving down a group, due to increase in principal quantum no. the distance between the nucleous and outermost shell electron will increase. Hence, ionic radii should increase steadily. But, due to scandide contraction (d-orbital contraction) and lanthanide contraction (f-orbital contraction) the increase in size in case of Se and Po are relatively low.
  • Ionization Energy: As the size decrease from up to down, the force of attraction between the nucleous and the outermost shell electron will also decrease Hence, the ionization energy will decrease down the group. But, due to scandide contraction (d-orbilal contraction) and lanthanide contraction (f-orbital contraction) the increase in size in case of Se and Po are relatively low. Hence, in case of Se and Po ionization energy will decrease to a little extent.
  • B.P./M.P.: Down the group, (he molecular weight increases. Hence, bp/mp increases down the group.
  • Electronegativity: As the size increases down the group, electronegativity should decrease down the group. But, due to scandide contraction the electronegativity of Se is somewhat larger than its previous one.
  • Oxidation State: The valence shell electronic configuration of gr. 16 metals are ns2np4. Hence, by losing six electrons these will attain the stable inert gas electronic configuration. Hence, the group oxidation state of gr. 16 elements are +6. But, due to inert pair effect the most stable oxidation state of Po is two unit less than the group oxidation state of Po i.e. its most stable oxidation state is +4.
  • Catenation: An element will show catenation property which is neither highly electronegative nor highly electropositive. Moreover, it should fonn M-M as well as M-O bonds. As oxygen is highly electronegative, it will show very little catenation property. Rather S shows better catenation property. Then, catenation property decrease down the group.

7. Group 17:

  • Ionic Radii: As we moving down a group, due to increase in principal quantum no. the distance between the nucleous and outermost shell electron will increase. Hence, ionic radii should increase steadily.
  • Ionization Energy: As the size decrease from up to down, the force of attraction between the nucleous and the outermost shell electron will also decrease Hence, the ionization energy will decrease down the group.
  • B.P./M.P.: Down the group, the molecular weight increases. Hence, bp/mp increases down the group.
  • Electronegativity: As the size increases down the group, electronegativity should decrease down the group.

8. Group 18:

  • Preparation: XeF2, XeF4 and XeF6, are prepared by the following way:
    Xe + F2(2 : 1) = XeF; Xe + 2F2 (1 : 5) = XeF4 ; Xe + 3F2 (1 : 20) = XeF6
  • Hydrolysis: XeF2, XeF4 and XeFo undergo hydrolysis to give the following products : XeF2 + H20 = Xe + O2 + HF ; XeF4 + H2O = Xe + O2 + XeO3 + HF ; XeF+ H20 = Xe + XeO3
  • Geometry:
  • XeF2: The no. of l.p. around Xe = 3 and the no. of bp. around Xe = 2. Hence, it is sp3d hybridized with linear shape.
  • XeF4: The no. of l.p. around Xe = 2 and the no. of b.p. around Xe = 4. Hence, it is sp3d2 hybridized with square planar shape.
  • XeF6The no. of l.p. around Xe = 1 and the no. of b.p. around Xe = 6. Hence, it is sp3d3 hybridized with distorted octahedral shape.
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