Linus Pauling, winner of two Nobel Prizes, developed innovative techniques to investigate chemical bonding and molecular structure. He won his first Nobel Prize for his investigation of genetic chemistry, and the second for his dedicated efforts to stop nuclear weapons testing.
Chemical bonds are formed to lower the energy of the system, the components of the system become more stable through the formation of bonds.
Everything wants to be more stable - its easy to lie down than stand up, bonding is Nature's way of allowing the elements to lie down.
If we examine the periodic table, we find that the elements in Group VIII (or 18), helium, neon, argon and so on, are particularly stable, so much so that they were once labeled the "inert gases".
G. N. Lewis (1916) suggested that bonds (covalent) formed to enable elements to attain this "noble gas configuration" .
We can see that in each case, sharing or transfer of electrons, results in a more stable system.
Electronic Configuration of first twenty elements.. Atoms tend to gain or lose their outer electrons to achieve a ‘full’ valence shell. INERT- GAS CONFIGURATION The outermost shell of the noble gas atoms are completely filled due to the presence of eight electrons (two in case of Helium).
Just as a summary to what each bond looks like…
A double covalent bond is formed by the sharing of 2 pairs of electrons between 2 atoms.
C has electronic configuration of 2,4 , has 4 valence electrons so it needs 4 more electrons to achieve the 8- electron inert gas configuration.
O has electronic configuration of 2,6, has 6 valence electrons so it needs 2 more electrons to achieve the 8- electron inert gas configuration
So 2 Oxygen atoms combine together with C by sharing 2 electrons each to form a molecule of CO 2 gas .
FORMATION OF TRIPLE COVALENT BOND IN NITROGEN (N 2 ) :---
A Triple Covalent bond is formed by the sharing of three pairs of electrons between two atoms.
The electronic configuration of N is 2,5 has 5 valence electrons, so it needs 3 more electrons to achieve the 8- electron structure of an inert gas & attain stability.
So 2 Nitrogen atoms combine together by sharing 3 electrons each to form a molecule of Nitrogen gas.
We are going to look at Polar Covalent now… What is polar covalent bond? - Polar covalent is a description of a bond that has an uneven distribution of charge due to an unequal sharing of bonding electrons. The boy is not equally sharing with anyone else but rather taking all the food for himself.
Physical Nature : Are solids which are in the form of crystals and relatively hard because of strong electrostatic force of attraction between oppositely charged ions and consequent close packed structure. These compounds are generally brittle and break into pieces when subjected pressure and stress. eg.the crystal lattice of NaCl has been already shown.
Melting and Boiling Points : As the ions in the ionic compounds are closely held together by strong interionic attractions, the solid ionic compounds are generally crystalline. A considerable energy is required to break the close packed crystalline structure and hence both melting and boiling points are high.
For e.g.when sodium chloride is added in water .,each Na+ ion and Cl- ion is surrounded by a number of molecules of water(H2O) which also carry charge. And are called Hydrated ions.
NaCl(s) +H 2 O
Na + (aq)+Cl - (aq)
3) Solubility : Ionic compounds are generally soluble in polar solvents like water and insoluble in non-polar solvents, or less polar solvents like alcohol, ether, benzene, etc.
4 ) Electrical Conductivity : The conductance through metals is because of movement of valence electrons. Since movement of ions and ionic solids is not possible due to the rigid structure, ionic compounds in the solid state either do not conduct electricity or are poor conductors. However, in the molten state or aqueous solution, ionic compounds conduct electricity due to mobility of ions.
Physical State : Covalent compounds can exist as solids, liquids or gases (mostly gases).
Solubility : Covalent compounds are generally soluble in non-polar solvents, or less polar solvents like alcohol, ether, benzene, etc. generally and insoluble in polar solvents like water.
Melting and Boiling Points : Molecules of an covalent compound are held together by relatively weaker forces as compared to that of ionic compounds. Therefore, melting and boiling points of covalent compounds are
generally low, as less energy is required to overcome these weak forces. 4) Electrical Conductivity : covalent compounds are poor conductors of electricity because they neither contain the ions nor the free electrons necessary for conduction. For example, Hydrogen Chloride gas i.e. HCl (g) is a poor conductor of electricity. But in water, it changes into hydrochloric acid i.e. HCl(aq). Since the acid can ionise in solution to form H+ and Cl- ions, it becomes a good conductor of electricity.
The ionic bond is a form of chemical linking of atoms in which electrons are transferred from one atom to another so that both atoms end up with completely filled electron shells. The alkali metals, such as potassium, shown here, have a single electron occupying the outermost shell in the atom. This is readily lost to halogen atoms, which require a single electron to fill their outermost shells. When the electron, which has a negative electrical charge, has been transferred, the alkali metal atom has become a positively charged ion, while the halogen atom has become a negatively charged ion. The two ions are held together strongly by electrostatic attraction.