ELECTRONEGATIVITY

The tendency of an atom in a compound to attract a pair of bounded electron towards itself is known as electronegativity of the atom. It is important to note that electron affinity and electonegativity both measure the electrons attracting power but the former refers to an isolated gaseous atom while the latter to an atom in a compound. Thus electron affinity is attraction for a single electron while electronegativity is for a pair of bonded electrons. Further electron affinity is energy while electronegativity is a tendency

Factor affecting the value of electronegativity

1.      The size of atom.

2.      Electronic configuration. Small atoms attract electrons more than the larger atomsone and are therefore more electronegativity. Secondaly, atom with filled shell of electrons, will tend to have higher electronegativity than those sparsely occupied ones.

Variations of electronegativity in the periodic table

1.      In a periodic , electronegativity increases from left to right. This is due to decrease in size and increase in nuclear charge. Thus the alkali metals posses the lowest value, while the halogens have the highest. Inert gases have zero electronegativity.

2.      In a group, electronegativity decreases from top to bottom. This is due to increase in atomic size.

 If an element exhibits various oxidations state, the atom in the higher oxidations state will be more negative due to greater attraction for the electron.

Electronegativity  may be expressed on the following three scales:

       I.            Mulliken’s scale: Mulliken  regards electronegativity as the average value of ionization potential and electron affinity of an atom.

 

Electronegativity =       ionization potential + electron affinity /  2

 

    II.            Allre-Rochow scale: Aller and Rochow defined electronegativity  as the electrostatic force exerted by the nucleus on  the valance electron.

 

 III.            Pauling  scale:  Paulling scale of electronegativity is the  most widely used. It is based on exess bond energies. He determined  electronegativity difference between the two atom and then  by assigning arbitrary values to few elements.

SOME OTHER PERIODIC PROPERTIES

1.      Atomic volume : It defined as the volume occupied by one gram atom of an element. Mathematically :

Atomic volume = gram atomic weight / density in solid state.

Unit of atomic volume are cc/mole. Atomic volume signifies the volume occupied by one mole of atom of the given element in solid state. Lower atomic volume generally leads ro higher density, increased hardness and brightness, higher melting and boiling points, less malleability and ductility.

·         While decreasing a group, the atomic volume generally increases which is due to increase in the number of sells through the valency electrons in a given group remains constant.

·         While going left to right across a periodic the atomic volume first decreases to a minimum and then increases. Francium has the highest atomic volume and boron has lowest atomic constant.

2.      Density : The density of the elements in solid state varies periodically with their atomic number. At first, the density increases gradually in a periodic and becomes maximum somewhere  for the central numbers then start decreases afterword.

3.      Melting point: The melting points of the element exibit some periodicity with rise of atomic number. It is observed that elements with low values of atomic volume have high melting points while element with high values of atomic volume have low melting points .

4.      Oxidation state: Oxidation number of an element in a compound is the total number of electrons it appears to have gained or lost during the formations of that particular compound.

5.      Megnatic properties : Megnatic properties of matter depend on the properties of the indivisual atom. A substance capable of being attracted into an magnetic fields is knpwn as paramagnetic


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