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  The tendency of an atom in a compound to attract shared electrons towards itself is known as electronegativity of an atom. Pauling gave an arbitrary scale to measure the electronegativity of different elements. This scale is based upon the calculation of bond energies, In this scale fluorine has the maximum value of electronegativity, i. e. 4.0. whereas noble gases have the minimum value, i. e. 0.0. On Mulliken scale, the average of ionization potential and electron affinity is known as electronegativity. In general, the smaller atoms as well  as the atoms with nearly filled shells of electrons, attract electrons more than larger atoms and are, therefore, more electronegative. Determination of Electronegativity   Pauling's scale: Pauling's   scale of electronegativity is based upon the calculation of bond energies. He considered the formation of AB covalent molecule as:  1/2A2+1/2B2 → AB   1/2(A-A) +1/2 (B-B) → A-B  According to Pauling, the bond dis...

    The chemical properties of the elements are also determined by the tendency of their atoms to accept an additional electron. This tendency is measured by the electron affinity, i.e., the energy released when a gaseous atom accepts an electron forming a free gaseous ion. X(g)+e = X-(g) + energy released     The energy released is measured in electron volt per atom (e. v. /atom) or   kilo joule per mole (k. j./mole ). Thus, larger is the energy released, the greater is the electron affinity. in other words, it is a measure of the force with which the added electron is bound by the nucleus of the atom. There may be first, second or higher electron affinity just like ionization potential.           O(g)+e = O-(g) + 1.47 e. v.          O- (g)+e = O2- (g) - 8.75 e. v.     The second and higher electron affinities are always negative because there occurs a repulsion between negatively charged ion and ...

           The minimum energy required to remove most loosely bound electron from the isolated gaseous atom is known as ionization potential or ionization energy.     

 Using electronic    configuration as the criterion ,we ordinarily recognise four general type of elements ; The inert gas elements  THe representative elements  The transition elements  The inner transition elements. "The classification of these elements into these groups is dependent on the extent to which the s,p,d and f orbitals are filled". (1) Inert Gases (a) s and p _orbital of the most shell of these elements are completely filled. The outermost electronic configuration in ns2np6. (b) HElium is also inert but it's electronic configuration is 1s2. (2) Representative or normal elements:- (a) Outermost shell of these elements is incomplete. The number of electrons is the outermost shell is less than eight. (b) Inner shells are complete. (c) s-  and p-block  elements except inert gases are called normal or representative elements. (3) Transition Elements ; (a) Last two shells of these elements namely outermost and penultimate shells are incomp...

  INTRODUCTION AND DEFINATION "The distance between the centre of of the nucleus of an  ion and the point upto which the nucleus has influence on its electron cloud." The limit of electron cloud  around nucleus cannot be determined with certainty. The radius of an ion is determined by determining  the internuclear distance in an ionic compound by X-ray measurements. This distance is then taken as the sum of the radii of the two ions involved. "If we know the radius of one ion, we  can calculate the radius of the other". "The atoms change into the ions either by the loss or gain of electrons". "A cation is always smaller than the corresponding atom ,whereas anion is always bigger than the corresponding atom". VARIATION OF IONIC RADII IN A GROUP:- Since the atomic size increases as we move down the group , therefore, ionic radius also  increases in moving from top to bottom in a group. Example:- ionic radii of alkali metals may be represented as: A...

  In the long form of the periodic table, several properties of elements such as atomic radii,ionic radii,ionization potential,electronegativity etc. vary in regular way in a group and in a period. Such properties are called periodic properties. These properties depend on electronic configuration of elements. ATOMIC RADIUS:- The distance between the centre of the nucleus and the electron cloud of the outermost shell is called atomic radius. Types of atomic radius:- Covalent radius, Vander Waals radius or collision radius. Crystal radius (metallic or atomic radius). Covalent Radius  It is one half of the distance between nuclei of two like atoms joined by a single covalent bond. example:- The distance between the nuclei of two chlorine atoms in a chlorine molecule is 1.98A⁰. In a heteronuclear  Diatomic molecule AB, if both the atoms are linked by a single covalent bond and have nearly the same electronegativity , the bond length dA-B is equal to sum of covalent radii of t...