When two isolated atoms are brought together then two types of force comes into play. Attractive force (\(F_A\)) between apposite nature of charge in atoms and repulsive force (\(F_R\)) between same nature of charge . The net force between two atoms is given by,
$$F_N=F_A+F_R\dotsm(1)$$If the magnitude of attractive force and repulsive force becomes equal then the net force between atoms is zero i.e.
For,\(|F_A|=|F_R| \Rightarrow F_N=0 \dotsm(2)\)
If net force in a molecule of a system becomes zero then states of equilibrium exists. The center of two atoms will remains separated by equilibrium separation.
If \(r<r_\circ \Rightarrow F_N=0\), repulsive net force
If \(r>r_\circ \Rightarrow F_N=0\), attractive net force
For many atoms the equilibrium separation is almost o.3 nm (i.e. 3\( A^\circ\)).
In the terms of energy, the force between two atoms is related as,
$$F=|\frac{dE}{dr}|=|\frac{dU}{dr}|$$
$$dU=F dr$$
$$U_N=\int F dr$$
$$U_N=\int F_A dr + \int F_R dR$$
$$U_N=U_A+U_R \dotsm(3)$$Where\(U_A\) & \(U_R\) represents attractive and repulsive energy for two isolated atoms.
The bonding energy between two atoms corresponds to energy of the molecule of system at equilibrium separation and is represented by \(U_\circ\) or \(E_\circ\) at \(r= r_\circ\). This energy is the amount of total energy required to completely dissociate to atoms from equilibrium separation. The force between two atoms is responsible for the formation of molecule and materials. The three primary types of bonds in solids are :-
In ionic bonding, there is a force between positive ion i.e. cation formed due to the transfer of valence electrons from one atom to another atom and anion negatively charge particle formed due to gain of electron. The nature of the force is electrostatic ( coulomb force ).
For example, The force between \(Na^+\) &\( cl^-\) is ionic bonding.
In terms of energy, the total energy of a molecule in ionic bonding is given by
$$E=E_A+E_R$$
$$E=\frac{-A}{R}+\frac{B}{R^n} \dotsm (4)$$Here, negative sign indicate the force is attractive amd positive sign indicate the some part of force repulsive and A & B are constant.
The simplest covalent compound is \(H_2\) gas.
In generally, the covalent bond is formed between nonmetallic elements in periodic table. The covalent bond is formed due to mutual sharing of electrons. It can also be described as the overlapping of orbital from different atoms.
For example: In the case of carbon atom total number of valence electrons (N)=4. So, carbon atom almost be covalently bonded with 8-N=4 atoms.
% ionic character =\(\biggl[1-e^\frac{(X_A-X_B)^2}{4}\biggr]\times 100\)%
Where, \(X_A\) and \(X_B\) represents the electronegativity of elements A and B.
Example: Diamond, Boron nitride, Quartz, silicon dioxid.
References:
Callister, W.D and D.G Rethwisch. Material Science and Engineering. 2nd. New Delhi: Wiley India, 2014.
Lindsay, S.M. Introduction of Nanoscience . New York : Oxford University Press, 2010.
Patton, W.J. Materials in industry . New Delhi : Prentice hall of India, 1975.
Poole, C.P. and F.J. Owens. Introduction To Nanotechnology. New Delhi: Wiley India , 2006.
Raghavan, V. Material Science and Engineering. 4th . New Delhi: Pretence-Hall of India, 2003.
Tiley, R.J.D. Understanding solids: The science of Materials. Engalnd : John wiley & Sons , 2004.
1. \(F_N=F_A+F_R\)
2.\(|F_A|=|F_R| \Rightarrow F_N=0\)
3.If \(r<r_\circ \Rightarrow F_N=0\), repulsive net force
If \(r>r_\circ \Rightarrow F_N=0\), attractive net force
4.\(U_N=U_A+U_R \)
5.Types:
.
No discussion on this note yet. Be first to comment on this note