Bonds are formed between atoms when they react with each other. For example – When two atoms of Hydrogen react with one atom of oxygen then bonds between two hydrogen atoms and oxygen are formed.
In most simple words Bond in Chemistry can be defined as sharing/transfer of electrons between atoms. This definition of a bond was proposed by G. N. Lewis in his paper titled “The Atom And The Molecule” in 1916. Based on this definition of bond, Lewis also proposed that “Second Period atoms in The Periodic Table tend to combine and form bonds by transferring or sharing electrons until each atom is surrounded by eight electrons in its highest energy or valence shell”. So it can also be said that Atoms combine with each other so as to achieve 8 electrons in valence shell, which is same as having Electronic Configuration as of Noble Gases.
But at the time of Lewis, it was not known that different orbits in an atom have suborbitals like s, p, d, f. But as more research was done by other chemists and new facts about what’s inside an atom? become visible to the world. Definition of what’s a Chemical Bond? also changed. Mostly nowadays Chemical Bonds are defined in terms of electron sharing considering suborbitals. But fundamental principle of atoms reacting with each other, which was proposed by Lewis still applies – Every atom wants to achieve Noble Gas Configuration.
That’s some information about what are bonds? Let’s now see what type of bonds exist in Chemistry?
There are different types of Bonds in Chemistry, the most common of these are Ionic Bonds, Covalent Bonds. Let’s see what is the meaning of both of these types of bonds.
What are Ionic Bonds?
Ionic Bonds form between two or more atoms by the transfer of one or more electrons between atoms. Electron transfer produces negative ions called anions and positive ions called cations. These then attract each other and consequently a kind of bond is formed between these, which is called Ionic Bond.
Example of an Ionic Bond Formation
Let’s consider example of formation of Ionic Bond between Sodium and Chlorine to form Sodium Chloride as per following Chemical Equation.
- Chlorine have 17 electrons, 17 protons and it’s Electronic Configuration is 1s2 2s2 2p2 3s2 3p5 so here Chlorine atom lacks one electron in 3p orbital for it to be a Noble Gas (specifically Argon which have electronic configuratin – 1s2 2s2 2p2 3s2 3p6 and is highly stable).
So during reaction between Chlorine and Sodium, chlorine will just go ahead and ask Sodium atom for a favour of one electron and guess what Sodium atom is already willing to loose one electron(why? discussed in point 2). So now chlorine atom will take one electron from sodium atom and then ultimately it will have 18 electrons, 17 protons. Which will make it an anion Cl– .
- As Sodium atom have electronic configuration 1s22s22p63s1 and for achieving it electronic configuration same as that of noble gas(Neon whose electronic configuration is 1s22s22p6) what it takes is just loosing an electron from 3s orbital. So sodium atom will just let 3s orbital electron to go to chlorine atom(it’s highly Electronegativity – Have higher tendency to attract electron as compared to sodium atom).
So after loosing 3s orbital electron to chlorine atom, sodium atom will be left with 10 electrons, 11 protons which will make it a cation Na+
- Now both of these cation Na+ and anion Cl– will be held together via Electrostatic Force, forming an Ionic Bond.
That’s how usuaully an Ionic Bond is formed.
Some Examples of Compounds having Ionic Bonds
- NaCl – Sodium Chloride
- NaBr – Sodium Bromide
- NaI – Sodium Iodide
- KF – Potassium Fluoride
- KCl – Potassium Chloride
- KBr – Potassium Bromide
- KI – Potassium Iodide
- CsF – Cesium Fluoride
- CsCl – Cesium Chloride
- CsBr – Cesium Bromide
- CsI – Cesium Iodide
- BeO – Beryllium Oxide
- BeS – Beryllium Sulfide
What are Covalent Bonds?
A Covalent Bond consists of the mutual sharing of one or more paris of electrons between two atoms. These electrons are simultaneously attracted by the two atomic nuclei. Covalent Bond forms when difference between electronegativies of two atoms is too small for an electron transder to occur from one atom to another.
Shared Electrons located in the space between two nuclei are called Bonding Electrons. The bonded pair is the glue which holds atoms together in the molecule.
- If one pair of electrons is shared between atoms then bond is Single Covalent Bond
- If two pairs of electrons is shared between atoms then bond is Double Covalent Bond
- If three pairs of electrons is shared between atoms then bond is Triple Covalent Bond
Example of a Covalent Bond Formation
Let’s see an example of formation of Covalent Bond between two atoms using Chlorine Molecule. So chlorine usually exists as molecule not as individual atom in the nature. Below is the mechanism for formation of chlorine molecule via covalent bond.
- Chlorine atom have Electronic Configuration – 1s2 2s2 2p2 3s2 3p5 so it lacks one electron to have stable noble gas configuration(Argon – 1s2 2s2 2p2 3s2 3p6). As other chlorine atom have same configuration then both of these will share one electron each and make a bond between two atoms. So now as two electrons are shared between both of atoms. That’s why now both will be having 6 electrons in 3p orbital, achieving stable noble gas configuration for each chlorine atom.
See below image
Some Examples of Compounds having Covalent Bonds
- Methane – CH4
- Ethane – C2H6
- Benzene – C6H6
- Acetic Acid – CH3COOH
- Citric Acid – C6H6O7
- Glucose – C6H12O6
I hope that this article about Chemical Bonds helped you to beter understand What’s meaning of Bonds in Chemistry?, What are types of Chemical Bonds?
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