Chemical Bonding – The Easy Way

Here, I am with a buzz of tutorials on concepts relating to CHEMICAL BONDING.

• Ionic Bond : An ion is an atom or group of atoms which have acquired charge due to loss or gain of electron(s). When an atom gains electron, negative ion (anion) is formed.   This character is similar to the fact that Income Tax department is always negative on  the people who gain lots of money and do not pay proper taxes. Whereas, when an atom looses electron, positive ion (cation) is formed. The transfer of electron always take place in outermost shell so as to attain the noble gas configuration that is 8 electrons in valence shell.
• When interaction takes place between two atoms OF OPPOSITE CHARGE, they are bonded by an ionic bond. Ionic bond is formed due to two ion interaction and are held together by electrostatic attraction. 
• Ionization energy: Lower the value of ionization energy of an atom, greater will be ease of formation of cation from it.
• Electron affinity: Higher the electron affinity of an atom, greater the ease of formation of the anion from it.
• Lattice Energy: when one mole of an ionic solid is formed from its constituent gaseous ions, the energy released is called lattice energy.
• Energies of formation of ionic substances: the energy included in formation of an ionic compound from its constituent elements may be considered as shown by Born-Haber Cycle for formation of 1 mole of NaCl from Sodium and Chlorine.
• Melting Point: Considerable energy is required to overcome the forces between ions in a crystal or electrovalent compound and break down the crystal lattice. Hence such compounds possess high melting and boiling point.
• Electrical Conductivity: When an electrovalent compound is molten or dissolved in any solvent of dielectric constant for example water, the binding force in the crystal lattice disappear and component ions become mobile. Under the influence of applied electrical field, ions get charged and thus act as charge carrier of current. Hence their melts or solutions conduct electricity.
• Solubility: Ionic compounds are soluble in polar solvents.
• Covalent bond: is formed when two atoms achieve stability by sharing of an electron pair, each contributing one electron to the electron pair.
• Dipole moment: is product of magnitude of charge on atoms and distance between atom(s).

Fajan’s Rules : When two oppositely charged ions approach each other closely, the positively charged cation attracts the outermost electroncs of anion and repel its positively charged nucleus.  This results in the distortion or polarization of anion followed by some sharing of electrons between two ions. In thie way, the bond becomes partly covalent in character.

Valence Shell Electron Pair Repulsion Theory

Gillespie and Nyhom gave the theory of VSEPR to predict and analyze molecular shapes  The summary of this theory is as follows:-

1. The shape of molecule is determined by repulsion between all of the electron pairs present in valence shell.
2. A loan pair of electrons take up more space round the central atom than a bond pair, since the loan pair is attracted to one nucleus whilst the bond pair is shared by two nuclei. It follows that repulsion between loan pairs is greater than repulsion between loan pair and bond pair. The presence of loan pairs on central atom causes slight distortion of bond angles from ideal shape. If angle between a loan pair, the central atom and order of repulsion between loan pairs and bond pairs of electron depends on the electronegativity difference between central atom and other atoms.
3. The magnitude of repulsions between bonding pairs of electrons depends on the electronegativity difference between central atom and other atoms.
4. Double bonds cause more repulsion than single bonds, and triple bond cause more repulsion than a double bond.

• «Previous Post
• Next Post »