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A positive ion is always smaller than the neutral atom ( Na is 1.570A and Na+ is 0.950A ) and a negative ion is always bigger than the neutral atom ( F is 0.720A and F- is 1.360A )

Within a period ( as shown in the Table ) isoelectronic positive ions ( having same number of electrons ) show a decrease in ionic radium from left to right due to increase in nuclear charge ( Na+ > Mg2+ > Al3+ ). Similarly for isoelectronic negative ions, ionic radium decreases from left to right ( O2 - > F- ).

Within a group of periodic table, similarly charged ions increase in size from top to bottom

( Li+ < Na+ < K+ or F - < Cl- < Br- < I - ) due to more electron shells.

The above table can be used to compare the strengths of ionic bonds in two compound in same medium.

Example : According to Coulomb’s law


The strength of the CaO bond is more than that of NaBr. Higher the strength, greater will be the melting point and higher will be the dissociation constant.

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4.1 Introduction
4.2 The Ionic Bonds
4.3 The Covalent Bonds
4.4 The Polar Bonds
4.5 Electronegativity
4.6 Others Bonds

Chapter 5

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