The graduation of the electronegativity of the elements in the periodic table
Electronegativity is the ability of the atom in the covalent molecule to attract the electrons of the chemical bond towards itself, There is an inverse relationship between the atomic size of the atom of an element, and its electronegativity in the modern periodic table.
In periods in the modern periodic table. the electronegativity increases by increasing the atomic number (from left to right). The electronegativity for the elements of the same period is directly proportional to the atomic number.
In groups in the modern periodic table, the electronegativity decreases by increasing the atomic number (from up to down). The electronegativity for the elements of the same group is inversely proportional to the atomic number.
The inert gases have not the electronegativity as they do not enter in the chemical reaction under the normal conditions.
The difference in the electronegativity between the elements forming the covalent molecules which measures the polarity of these molecules, So, the covalent compounds are classified into the polar compounds and the non-polar compounds.
The polar compounds are the covalent compounds in which the difference in the electronegativity between their elements is relatively high.
When the difference in the electronegativity between the elements of a covalent compound molecule equals zero, the bond in this molecule is called the pure covalent bond. As in oxygen molecule and hydrogen molecule.