Saturday, 14 July 2012

P-BLOCK ELEMENTS OF THE MODERN PERIODIC TABLE. What are P- BLOCK ELEMENTS ? Their POSITION in the Periodic Table and their PROPERTIES..!

P - Block Elements

 
Elements belonging to the group 13 ( i.e group IIIA ) to group 17 (i.e group VIIA ) of the periodic table along with the group 18 i.e the zero group elements together form the p-block of the periodic table.
In the p-block elements the last electron enters the outermost p orbital. They have 3 to 8 electrons in the outermost shell. As we know that the number of p orbitals is three and, therefore, the maximum number of electrons that can be accommodated in a set of p orbitals is six. Hence there are six groups of p-block elements in the periodic table numbering from 13 to 18. The First group of the p-block i.e the group IIIA is commonly called as Boron group,the second group i.e the group IVA is called Carbon group,the third group i.e the group VA is called Nitrogen group, the fourth group i.e the group VIA is called Chalcogens ,the fifth group i.e the group VIIA is called Halogens and the sixth group i.e the zero group or group 18 is called Inert or Noble gases group. In the p-block all the three types of elements are present, i.e. the Metals,Non-Metals and Metalloids .The zigzag line in the p-block separates all the elements that are metals from those that
are non-metals.Metals are found on the left of the line, and non-metals are those on the right. Along the line we find the metalloids. Due to the presence of all types of elements the p-block show a lot of variation in properties.

Classification of elements in the p-block of the Periodic Table :-
The elements in the p-block of the periodic table consists of all types of elements i.e metals , non-metals and metalloids.

a) Metals :-
1)Aluminium, 2)Gallium, 3)Indium, 4)Thallium, 5)Tin, 6)Lead, 7)Bismuth .

b)Non-Metals :-
1)Helium, 2)Carbon, 3)Nitrogen, 4)Oxygen, 5)Fluorine, 6)Neon, 7)Phosphorus, 8)Sulphur, 9)Chlorine, 10)Argon, 11)Selenium, 12)Bromine, 13)Krypton, 14)Iodine, 15)Xenon, 16) Radon.

c) Metalloids :-
1)Boron, 2)Silicon, 3)Germanium, 4)Arsenic, 5)Antimony, 6)Tellurium, 7)Polonium, 8)Astatine.

Characteristic Properties of elements in p-block of Modern Periodic Table :-

1) Electronic Configuration :- The general valence shell electronic configuration of p-block elements is ns 2 np 1-6 (except for He). The inner core of the electronic configuration may, however, differ.
The General electronic configuration shown by elements from group13 to 18 of p-block is as given below :-
Group 13 (Boron family)     :- ns 2 np 1 .
Group 14 (Carbon family)   :- ns 2 np 2 .
Group 15 (Nitrogen family) :- ns 2 np 3 .
Group 16 (Oxygen family)   :- ns 2 np 4 .
Group 17 (Halogen family)  :- ns 2 np 5 .
Group 18 (Noble gases)       :- ns 2 np 6 (except Helium) .
The general electronic configuration of Helium is 1s 2 . Due to their distinct electronic configuration p-block elements show a lot of variation in properties.

2) Metallic Character :- As stated earlier p-block contains all types of elements i.e metals,non-metals and metalloids . The p-block is the only region of the periodic table to contain metalloids .The non metallic character decreases down the group whereas there is a gradual increase in non-metallic character from left to right in the p-block. The metallic character tends to increase down each group whereas it decreases as we go from left to right across a period. In fact, the heaviest element in each p-block group is the most metallic in nature.

3) Atomic Density :- The Atomic Density of elements in p-block increases down the group, this is due to increase in the size of the atom down the group. Whereas it decreases as we move from left to right across the period,this is due to the decrease in atomic size of all elements in the p- block across the period. Of all the elements, aluminum is of very low density and is widely used as a structural material.

4) Melting and Boiling points :- The Melting and Boiling points gradually increases down the group because the molecular mass increases down the group and hence the intermolecular forces increases.

5) Oxidation state :- The p-block elements show a variable oxidation state . The oxidation states increases as we move from left to right in the periodic table. The maximum oxidation state shown by a p-block element is equal to the total number of valence electrons . According to this, the oxidation states shown by different groups is as follows :-
Boron family (Group 13) :- +3
Carbon family ( Group 14) :- +4
Nitrogen family (Group 15) :- +5
Oxygen family ( Group 16) :- +6
Halogen family (Group 17) :- +7
Noble gases ( Group 18) :- +8

But in addition to this p-block elements may also show other oxidation states which normally , but not necessarily , differ from total number of valence electrons by unit of two. The other oxidation state two unit less than the group oxidation state shown by different groups is as follows :-
Boron family (Group 13) :- +1
Carbon family ( Group 14) :- +2 , -4
Nitrogen family (Group 15) :- +3, -3
Oxygen family ( Group 16) :- +4, +2, -2
Halogen family (Group 17) :- +5, +3, +1, -1
Noble gases ( Group 18) :- +6, +4, +2 .

However, the relative stabilities of these two oxidation states i.e the group oxidation state and the other oxidation state two unit less than the group oxidation state , may vary from group to group .

6) Atomic and Ionic radii :- As we move down the group in the p-block one extra shell than the preceding element gets added into the next element. This ultimately increases the atomic and the ionic radius of every next element down the group , which finally shows that the atomic and the ionic radii increases down the group.The trend is not same across the period. As we move from left to right in a period the Atomic radii and the Ionic radii of p-block elements decreases . The Atomic radius increases greatly from Boron to Aluminum.This increase is due to greater screening effect caused by the eight electrons
present in the penultimate shell.

7) Electrode Potential :- The p-block elements generally have a positive electrode potential. It generally decreases down the groups.
For eg. Consider the electrode potentials of the halogen group :-
Fluorine = 2.87 V
Chlorine = 1.36 V
Bromine = 1.09 V
Iodine = 0.53 V
From the above analytical data we can say that the electrode potential
in the p-block decreases down the groups .

8) Ionisation Energies :- The p-block elements have high ionization potentials. The ionisation energies of p-block elements increases from left to right in a period due to increasing effective nuclear charge.
According to the general trends the ionisation energy values decreases down the group but do not decrease smoothly as expected. Non-metals have high Ionisation Energies than metals. It is maximum for a noble gas because noble gases have completely filled configuration. Some elements at the bottom of a group like Lead, Tin, Thallium, Bismuth,
etc. behaves almost as a metal with very low ionization energies.

9) Magnetic Properties :- The elements Radon, Astatine, Iodine and Polonium of the p-block are Non-Magnetic in nature. The element Tin is Paramagnetic and the rest all elements of the p-block are Diamagnetic in nature.

10) Complex Formation :- The smaller size and the greater charge of the elements of different groups of p-block enable them to have a greater tendency to form complexes than the s-block elements. The complex formation tendency decreases down the group as the size of the atoms increases down the group.

11) Chemical Reactivity :- The Chemical Reactivity of elements in the p-block increases as we move from left to right in a period. But as we move down in a group the chemical reactivity of elements decreases down the group.

i) Reactivity of Noble gases :-
All the orbitals of the noble gases are completely filled by electrons and it is very difficult to break their stability by the addition or removal of electrons. Thus the noble gases exhibit very low chemical reactivity. Because of their low reactivity noble gases, are often used when an nonreactive atmosphere is needed, such as in welding.

Preceding the noble gas family there are two chemically important groups of non-metals. They are the halogens (Group 17) and the chalcogens (Group 16). These two groups of elements have high electron gain enthalpies and can readily add one or two electrons forming an anion to attain the stable noble gas configuration thus showing good
chemical reactivity.

ii) Reactivity of Halogens :-
a) All halogens are naturally found in a combined state.
b) Fluorine reacts readily with almost any substance coming in contact with it.
c) Chlorine, Bromine, and Iodine are progressively less reactive but still form compounds with most other elements, especially metals.
d) All the halogens are strong oxidising agents.The halogens oxidize other Substances, but themselves get reduced.
e) All halogens combine directly with sodium to form sodium halides.
f) All halogens react with red phosphorus to form phosphorus halides.
g) Halogens react readily with alkali metals forming salts.
h) The presence of Chlorine,Bromine and Iodine can be tested by the treatment of acidified silver nitrate solution.

iii) Reactivity of group VIA Elements ( Chalogens ) :-
a) As we approach to the right-hand side of the periodic table, similarities among the elements within a group become greater. This is true for the group VIA. Except Polonium, which is radioactive and usually omitted from all discussions.
b) All members of the group VIA form X 2– ions when combined with highly electropositive metals.
c) The tendency to be reduced to the - 2 oxidation state decreases significantly from top to bottom.
d) At ordinary temperatures and pressures, oxygen is a gas. It exists in either of the two allotropic forms :- O 2 , which makes up 21 percent of the earth's atmosphere, or O 3 (ozone), which slowly decomposes to O 2 .
e) The ozone itself absorbs longer-wavelength ultraviolet radiations , preventing these harmful rays from reaching the earth's surface which would otherwise increase the probability of human skin cancer and can also cause other environmental problems.
f) The Compounds of selenium and tellurium are of little commercial importance as they are toxic.

iv) Reactivity of Metalloids :-
a) The chemical reactivity of the metalloids depends on the substance with which it is reacting. For example:- Boron behaves as a nonmetal when reacting with sodium, but it acts as a metal when reacting with fluorine .
b) Thus from the above example we can say that Metalloids show variable chemical properties.
c) They act like non-metals when they react with metals whereas they act like metals when they react with non-metals.
d) Due to their low electronegativity, they are usually oxidized in reactions. The oxides of metalloids are usually amphoteric .

v) Reactivity of group VA Elements :-
a) All the group VA elements form trihydrides when reacted with hydrogen.
b) The reactivity decreases down the group.
c) The elements in the group VA either form trioxides or pentoxides when reacted with oxygen.
d) Also they form trihalides or pentahalides when reacted with halogens.
e) All the group VA elements react with metals to form binary compounds.
f) The most important compounds of the group VA elements are those of nitrogen and phosphorus.
g) Nitrogen and phosphorus are most commonly used as fertilizer.

vi) Reactivity of group IIIA Elements :-
1) Unlike groups IA and IIA, none of the group IIIA elements react directly with hydrogen to form hydrides.
b) Also all the group IIIA elements react with halogens to form trihalides instead of simply halides like group IA and IIA elements.

vii) Reactivity of group IVA elements :-
a) Carbon have a ability to form strong bonds with other carbon atoms and thus form a tremendous variety of organic compounds
b) In the +4 oxidation state lead acts as a strong oxidizing agent, gaining two electrons and after gaining electrons it gets reduced to the +2 oxidation state.
c) Also in the +4 oxidation state lead forms covalent compounds and bonds strongly to carbon.
d) Besides the metals themselves, some tin and lead compounds are of commercial importance. For eg :- Tin(II) fluoride (stannous fluoride), is added to some toothpastes to inhibit dental cares.
e) Lead is also found in two main commercial applications. One, the lead-acid storage batteries used to start cars and the other is in the automobile fuel.

12) Conductivity :- The conductivity of elements in p-block increases down the group. Generally the metals in the p-block are good conductors of heat and electricity whereas the non-metals are poor conductors of heat and electricity. The conductivity of metalloids
lies in between the metals and non-metals.

13) Colour :-
Colour of group IIIA elements :-
All the group IIIA elements are silvery solids except boron which is brown solid.
Colour of group IVA elements :-
Carbon is black in colour whereas silicon and germanium have reddish brown or dull grey or black colour. Lead has a bluish-white colour. 

Colour of group VA elements :-
Nitrogen is a colourless.
Phosphorus exists in white colour.
Arsenic is found in yellow and grey solid form.
Antimony is found in a amorphous grey form.
Bismuth is silvery white in colour . 

Colour of group 16 elements :-
Oxygen is a gas and is colourless .
Sulphur is pale yellow in colour.
Tellurium is Silvery-white in colour . 

All the Halogens are coloured. They have following colours :-
Fluorine :- Pale yellow.
Chlorine :- Greenish yellow.
Bromine :- Reddish brown.
Iodine :- Violet black.

Noble Gases have following colours :-
Helium is red, Neon is orange, Krypton is purple whereas Xenon is
white in colour.
Radon is colourless.

14) Flame colouration :- Not all but a few p-block elements impart characteristic colour to the flame. Arsenic impart Blue colour to the flame. Boron impart Bright green Colour to the flame. Copper (I) impart Blue colour whereas Copper(II) (non-halide ) impart Green
colour to flame whereas Copper(II) (halide) impart Blue- green colour to flame. Indium and selenium impart Blue colour to flame. Phosphorus impart Pale bluish green colour whereas Lead impart Blue/White colour to flame. Antimony and Tellurium impart Pale green colour. Thallium impart Pure green colour to flame.

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