Q. Write a short note on groups?

 Groups:

            The vertical columns are called groups.

 Sub-Group:

            Basically, there are eight groups but each group is further divided into A and B subgroups.

Sub-Group A:

        The elements of subgroup A  are called main or Representative elements, as the properties of these elements are represented by Valence Electrons.

 This group includes S- Block ( IA to IIA) elements and P-block(IIIA to VIII A)  elements.

Sub-Group B:

         The elements of subgroup B are called transition elements because the properties of these elements show a gradual change of transition between the two sets of Representative elements.


Transition Elements:

         The elements of subgroup B are called Transition Elements because the properties of these elements show a gradual change or transition between the two sets of Representative elements.

Elements of a group have similar valence shell configuration hence have similar properties. The group number indicates the total number of electrons in the valence shells of that element.


Types of Transition Elements:

              Transition elements are divided into two types.

(I) Outer Transition Elements ( filled d orbit)

(II)  Inner Transition Elements ( filled f orbit) 


 Properties of Group IA(Alkali metals) or (Lithium family):

                This group includes S block and p block elements including the following elements

 Sodium, Potassium, Rubidium, and Cesium and Francium.


 Their valence shell contains 1 electron only and on reaction, they lost the electron and form univalent positive ions( M+1).

Na=11

K=1S1

L=2S2,2P6

M= 3S1

 They are highly reactive metals with low melting points. Francium is Radioactive.

 Their atomic radius, atomic volumes, and ionic radius increase from Li to Cs due to the addition of extra shell to each element, and due to same reason melting and boiling points decrease downward.

 they are called alkali metals because they form water-soluble bases such as sodium hydroxide and potassium hydroxide.

                   For Example: 

                                    Na + O2 ------>  NaO + H2O ----->  NaOH

 Properties of group IIA (The Alkaline Earth Metals Or Beryllium Family):

 It includes  Magnesium, Calcium, Strontium, Barium, and Radium.

 Their valence shell contains two electrons. On reaction, they lose these two electrons and form divalent positive ions( M2+).


 Electronic Configuration:

G= 12

K=1S1

L=2S2,2P6

M= 3S2

Radium is Radioactive.

These elements are a bit harder having higher melting and boiling points than the alkali metals but they have smaller atomic and ionic radii and atomic volumes.

Down the group, they do not show a regular trend in melting boiling points and densities.

These elements form metallic oxides and basic oxides.

For Example: 

         K(S) + O2 ----> K2O -----> KOH

        Mg + O ----> MgO + H2O ----> Mg (OH)2

        Ca + O2 ------> CaO + H2O -----> Ca(OH)2


 Properties of Group IIIA( the Boron family):


 It includes Boron, Aluminium, Gallium, Indium, and Thallium.

 Their valence shell contains 3 electrons, they exhibit a valency of 3+ and forms M+3 Ions.

Except for Boron, they are highly electropositive elements having a metallic character which increases down the group due to an increase in the atomic volume.

Electronic Configuration:

B=5

K=1S2

L=2S2,2P1

Boron is a  metalloid. A metalloid is an element that has some properties of metal and some properties of Non-metals.


Properties of Group IVA( Carbon family):

Carbon, Silicon, Germanium, Tin, and Lead.

Their valence shell contains four electrons. Carbon, Silicon, and, Germanium form covalent compounds whereas Tin and Lead exhibit a variable valency of 2 and 4.

Down the group, Atomic radii and Atomic volume increase due to the addition of a new shell, and for the same reason, the metallic character increases down the group.

Carbon and Tin exist in different allotropic forms.


Properties of Group VA( Nitrogen Family):

It includes Nitrogen, Phosphorus, Arsenic, Antimony and, Bismuth.

Of these elements Nitrogen and Phosphorus are non-metals, Arsenic and Antimony e are metalloids, and Bismuth is a metal.

Their valence shell contains five electrons.

There is a large variation of properties as we go down the group.

Nitrogen exists as a diatomic molecule (N2)  and forms a number of oxides as NO, N2O, NO2, N2O4, and N2O5.

Due to its small atomic size and large and Ionization potential, nitrogen has a tendency to accept these electrons to form nitride ions (N3-).

Phosphorus exists as a P4 molecule.

Except for Nitrogen, all exist in more than one allotropic form.


Properties of Group VIA( Oxygen Family):

It includes Oxygen, Sulphur, Selenium, Tellurium, and Polonium.

Of these Oxygen and Sulphur are non-metals, Selenium, Gallerium are metalloids, and Polonium is a metal.

All of the elements exhibit the property of allotropy for example allotropic forms of Oxygen are Oxygen and ozone.

Oxygen and Sulphur from diatomic negative ions, their Valence shell contains 6  electrons.

 


Properties of Group VIIA( The Halogens):

It includes Fluorine, Chlorine, Bromine, Iodine, and Astatine.

Except for Astatine( which is a metalloid), all others are non-metals and exist as diatomic molecules.

At room temperature Chlorine and Florine are gases, Bromine is a liquid and Iodine is solid.

Their valence shell contains 7 electrons.

They have high ionization energy and large negative electron affinity.  They easily accept an electron.


Electronic Configuration:

Cl= 17

K=1S2

L=2S2,2P6

M=3S2,3P5


Properties of Group VIII A (Inert or Noble Gases):

 It includes Helium, Neon, Argon, krypton, Xenon, and  Radon.

 Their valence shell contains 8 electrons except for Helium which contains two electrons.

 With the exception of Krypton and Xenon (which have a large atomic volume so slightly reactive under drastic conditions), the rest of these elements are totally inert chemically.

 The reason is that they have completely filled outer shells, a condition that represents greater stability.


Properties of Group IB to VIIIB(Transition Elements):

These are metals. In these elements besides the valence shell penultimate shell is also incomplete.

In chemical reactions, they show more than one valency, for example:

                         Fe++, Fe+++, Cu++, Hg+, Hg++ 


These elements in compounds have characteristic colors. For example:

                                       CuSO4             Blue

                                        FeSO4            Green

                                        NiSO4             Green 


 These elements with filled (d and f orbital) are called transition elements.

 

                Types of Transition Elements:

 

Outer Transition Element:

Outer Transition Elements fill d orbital.

For example Cu, Fe, Zn.

Inner Transition Elements:

Inner Transition Elements fill f orbital.

For example Ce, Th, Pr, Pa.