Chap#3, Periodicity of Elements, Some Properties of Atom,

 Chap#3

               Periodicity of Elements

Q1. Differentiate between metal, nonmetals, and metalloids?

Metals	Non-Metals	Metalloids
They are electropositive elements i.e they lose electrons to form cations.	They are electronegative elements i.e they gain electrons to form anions.	These are the elements that exhibit dual character.
They form basic oxides	They form acidic oxides.	Their oxide is amphoteric i.e basic as well as acidic in nature.
They are good conductors of electricity and heat.	They are bad conductors of heat and electricity.	They are semi-conductors of heat and electricity.
All of them have a luster and are malleable(i.e can be1 spread into sheets)  and ductile.	All of them have no luster and are not malleable (i.e cannot be spread into sheets) and are non-ductile.	All of them have no luster and are not malleable(i.e cannot be spread out into sheets) and are non-ductile.
They have high melting and boiling points.	They have low melting and boiling points.	-------------
In the periodic table elements of group IA, IIA, and all transition elements are metal, some of the  Elements of group IIIA, IVA, VA, and VIA are all  metal	In the periodic table majority of elements of the P block group III-A, IVA, VA, VIA, VIIA, and VIIIA are non-metals.	In the periodic table, metalloids are Boron of group IIIA, Silicon and Germanium of group IVA,  Arsenic, Antimony of group VA, and  Polonium of group VIA, Astatine of VIIA.
Most of them are solid except Mercury.	Most of them are gases.	-------------

Q2.Describe some periodic properties of atoms?

       Some Properties of Atom:

        Atomic Radius:

Definition:

            The term Atomic Radius is defined as half the distance between two adjacent nuclei of two similar atoms in touch with each other.

Unit:                                   

           It is measured in Angstrom unit(A0 or A.U) 1A0 = 10-8cm.

           The Atomic Radius depends upon the number of shells and nuclear charge in an atom.

 In Group:

           In the periodic table, the atomic radius increases down the group due to the addition of a new shell in each atom.

                            Atomic Radii Down a Group:

Elements of Group IIA	Atomic Radii  in A0
Be	1.12
Mg	1.36
Ca	1.97
Sr	2.15
Ba	2.22

IN PERIOD:

                    In a period atomic radii decrease from left to right due to the increase in the number of protons i.e increase in nuclear charge, which results in the stronger pull on electrons by the nucleus.

                                             Atomic Radii in a Period:

Elements	Na	Mg	Al	Si	P	S	CI
Atomc Radii in A0	1.51	1.36	1.25	0.77	0.70	0.66	0.64

 Ionization Energy:

 Definition:

              It is defined as the minimum energy required to remove an electron from a gaseous atom in its ground state. It is measured in K.J/ Mole.

 Unit:

        H(g) + ENERGY-----> H+ + e- I.E= + 1312 K.J/Mol

 In Group:

            Down a group, in the periodic table, the ionization energy decreases because the addition of a new shell decreases the hold of the nucleus on Valence Electrons.

 In Period:

           Ionization energy increases from left to right in a period because the addition of protons in the nucleus increases the nuclear charge thereby increasing the force of attraction on electrons.

 First Ionization Energy:

           The amount of energy required to remove the first electron is called “First Ionization   Energy”  for subsequent electrons it is called second, third fourth ionization energy.

 Electron Affinity:

 Definition:

          Electron Affinity is defined as energy change that occurs when an electron is gained by an atom in the gaseous state.

 Units:

             It is measured in kilojoule per mole (K.J/Mol) or electron volt per atom( e.v per atom).

                                            O(g) + e-(g) E.A = 142 K.J/Mol      (Exothermic)

                                      O- + e- ----> O2-(g)  E.A = + 780KJ/Mol   (Endothermic)

           Electron Affinity for the addition of the first electron is negative. Electron Affinity depends upon the atomic size and nuclear charge.

  In  Group:

               Down a group in the periodic table, electron affinity decreases because the addition of a new shell to each atom decreases its force of attraction.

ELEMENT	Electron Affinity in KJ/Mol
F	-333
CI	-348
Br	-324
I	-295

Q2. Why fluorine has an abnormally low electron affinity?

       Reason:

                   Florine has abnormally low electron affinity because due to its very small size it does not accept electrons easily.

 In Period:

        In a period the electron affinity increases from left to right because successive atoms have higher nuclear charge and attract the incoming electron more towards itself.

Element	Li	Be	B	C	N	D	F	Ne
E.A in KJ/Mole	-58	0	-23	-128	0.2	-142	-332	0

 Electronegativity:

 Definition:

                  Electronegativity is identified as the relative tendency of an atom in a molecule to attract shared pair of electrons towards itself.

 Unit:

                   It is denoted by a number and has no unit.

 In Group:

                  Down a group electronegativity decreases as due to the addition of a new shell, the power of the nucleus to attract an electron decreases.

In Period:

                  In a period from left to right, it increases due to an increase in the nuclear charge.

 Nature of Bond:

                 The difference in the electronegativity of two combining atoms decides the nature of the Bond that is formed between them and affects the properties of molecules.

                                                QUESTIONS

Q1. Differentiate between metals, nonmetals, and metalloids?

 Q2.Describe some periodic properties of atoms?

Q3. Why Florine has abnormally low electron affinity?