A chemical bond is a lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds. In other word, Chemical compounds are formed by the joining of two or more atoms. A stable compound occurs when the total energy of the combination has lower energy than the separated atoms. The bound state implies a net attractive force between the atoms known as a chemical bond.
We know, a chemical bond is an attraction between atoms. This attraction may be seen as the result of different behaviors of the outermost or valence electrons of atoms. These behaviors merge into each other seamlessly in various circumstances, so that there is no clear line to be drawn between them. However, it remains useful and customary to differentiate between different types of bond, which result in different properties of condensed matter.
There are mainly three types of chemical bonding. They are
- Ionic Bonding 2. Covalent Bonding & 3. Metallic Bonding.
There are also other chemical bonding like
- Hydrogen Bonding
- Van der Waals Bonding
- Co-ordinate covalent bond
Different types of chemical bonding are discussed below…
In chemical bonds, atoms can either transfer or share their valence electrons. In the extreme case where one or more atoms lose electrons and other atoms gain them in order to produce a noble gas electron configuration, the bond is called an ionic bond.
Typical of ionic bonds are those in the alkali halides such as sodium chloride, NaCl.
Covalent chemical bonds involve the sharing of a pair of valence electrons by two atoms, in contrast to the transfer of electrons in ionic bonds. Such bonds lead to stable molecules if they share electrons in such a way as to create a noble gas configuration for each atom.
Hydrogen gas forms the simplest covalent bond in the diatomic hydrogen molecule. The halogens such as chlorine also exist as diatomic gases by forming covalent bonds. The nitrogen and oxygen which makes up the bulk of the atmosphere also exhibits covalent bonding in forming diatomic molecules.
There are mainly three types of covalent bond depending upon the number of shared electron pairs…
They are …
SINGLE COVALENT BOND
DOUBLE COVALENT BOND
TRIPLE COVALENT BOND
The properties of metals suggest that their atoms possess strong bonds, yet the ease of conduction of heat and electricity suggest that electrons can move freely in all directions in a metal. The general observations give rise to a picture of “positive ions in a sea of electrons” to describe metallic bonding.
Now we shall discuss the other types of chemical bonding…
Hydrogen bonding differs from other uses of the word “bond” since it is a force of attraction between a hydrogen atom in one molecule and a small atom of high electronegativity in another molecule. That is, it is
an intermolecular force, not an intra-molecular force as in the common use of the word bond.
When hydrogen atoms are joined in a polar covalent bond with a small atom of high electronegativity such as O, F or N, the partial positive charge on the hydrogen is highly concentrated because of its small size. If the hydrogen is close to another oxygen, fluorine or nitrogen in another molecule, then there is a force of attraction termed a dipole-dipole interaction. This attraction or “hydrogen bond” can have about 5% to 10% of the strength of a covalent bond.
Hydrogen bonding has a very important effect on the properties of water and ice. Hydrogen bonding is also very important in proteins and nucleic acids and therefore in life processes. The “unzipping” of DNA is a breaking of hydrogen bonds which help hold the two strands of the double helix together.
Van der Waals Bonding
Water molecules in liquid water are attracted to each other by electrostatic forces, and these forces have been described as van der Waals forces or van der Waals bonds. Even though the water molecule as a whole is electrically neutral, the distribution of charge in the molecule is not symmetrical and leads to a dipole moment – a microscopic separation of the positive and negative charge centers. This leads to a net attraction between such polar molecules which finds expression in the cohesion of water molecules and contributes to viscosity and surface tension. Perhaps it is fair to say that van der Waals forces are what holds water in the liquid state until thermal agitation becomes violent enough to break those van der Waal bonds at 100°C. With cooling, residual electrostatic forces between molecules cause
most substances to liquify and eventually solidify (with the exception of helium, which never becomes a solid at atmospheric pressure).
Even nonpolar molecules experience some van der Waals bonding, which can be attributed to their being polarizable. Even though the molecules don’t have permanent dipole moments, they can have instantaneous dipole moments which change or oscillate with time. These fluctuations of molecular dipole moments lead to a net attraction between molecules which allow nonpolar substances like carbon tetrachloride to form liquids. Examination of the dipole electric field shows that the electric field from one instantaneous dipole will tend to polarize a neighboring molecule such that it will be attracted – sort of the electrical analog to a bar magnet magnetizing a paper clip so that it will be attracted to the magnet. (This happens regardless of which pole of the magnet is brought close to the paper clip.) The weaker van der Waals forces in nonpolar liquids may be manifested in low surface tension and low boiling points.
Coordinate covalent bond
A covalent bond is formed by two atoms sharing a pair of electrons. The atoms are held together because the electron pair is attracted by both of the nuclei.
In the formation of a simple covalent bond, each atom supplies one electron to the bond – but that doesn’t have to be the case. A coordinate bond (also called a dative covalent bond) is a covalent bond (a shared pair of electrons) in which both electrons come from the same atom.
So , there you go… We have come to the conclusion of today’s lesson. Hope you have enjoyed it & understand chemical bonding!
Hope to see you next time. Till then, Happy Learning…