Water is one of the most essential substances for the existence of life. Since life on the earth began in the oceans, and since no living thing can survive without water, it is rightly called the source of life.
Water forms a large part of the body mass of all living organisms — 90% of human blood is water. Water has the ability to dissolve a number of substances. Therefore, it serves as the liquid medium in which all reactions within the living body take place.
Fruits and vegetables contain water in them. Even dry-looking substances like wood, peas, beans, grams, etc., contain some amount of water.
Molecular formula: H2O, relative molecular mass-18 amu. One molecule of water contains two atoms of hydrogen and one atom of oxygen.
Chemical Name: Dihydrogen monoxide.
Is H2O an ionic or covalent bond?
Water H2O is a covalent bond in which two single covalent bonds are formed. Both atoms hydrogen as well as oxygen belong to the non-metal category, have high electron affinity and high ionization energy.
Before proceeding, you should remember, electron affinity is the affinity to acquire an electron from another atom. Whereas ionization means the energy required to remove an electron from the outermost shell.
H2O Covalent bond occurs because both of the atoms want to achieve stability and this can happen if only both of them have completed the outermost shell.
Moving further, To put them stable, we have two options whether to
- Take an electron from one atom and give it to another or
- Allow them to share electrons with each other.
But hydrogen and oxygen atoms have high ionization energy. A huge amount of energy is required to expel electrons to complete an octet.
As both have high ionization energy, this means we need a huge amount of energy to take away electrons from one and give them to the other. Not only this but also, both two oxygen atoms and a hydrogen atom have high electron affinity. they are in strong desire to acquire electron instead of giving them to other.
At this moment, on seeing their behavior, H2O can never be an Ionic bond instead of a Covalent bond. Both of the atoms do not accomplish the requirement of becoming an ionic bond.
Why Do atoms form Covalent Bond?
The atoms of all elements, other than the inert gases, combine because they have incomplete valence shells and tend to attain a stable configuration. Hydrogen and oxygen atom is one of them.
Kossel and Lewis, in 1916, independently put forward the octet theory of valency or the electronic theory of valency. According to them, inert gases have a stable electronic configuration.
Elements tend to combine with one another to attain the stable electronic configuration of the nearest inert gas, i.e. 8 electrons in its valence shell. This is known as OCTET RULE. However, in the case of helium, the valence shell has 2 electrons and this is known as DUPLET RULE.
This is achieved either by gaining electrons or losing electrons or sharing electrons with other atoms of the same element or another element.
The number of electrons gained, lost, or shared to attain the octet in the outermost shell, gives the combining capacity of the element that is, its valency.
As a result of this redistribution of electrons, a force of attraction develops between atoms, which binds them together to form molecules. This force is known as a chemical bond.
A chemical bond may be defined as the force of attraction between the two atoms that bind them together as a unit called a molecule.
The chemical combination of atoms involves the redistribution of electrons so as to leave each atom with a stable electronic configuration.
Water H2O a Covalent Bond
During bond formation, an atom is always in an effort to achieve the nearest noble gas configuration. For example, if hydrogen has one proton and electron. Its nearest noble gas is helium. So, hydrogen does not move to the configuration of neon. It only needs one electron to complete the outermost shell. Similarly, oxygen also achieves the nearest noble gas of neon. The neon (Z=10= K,L = 2,8) outermost shell has 8 electrons.
To attain a stable electronic configuration of the nearest noble gas hydrogen needs one electron and oxygen needs two electrons.
In the case of a water molecule, each of two hydrogen atoms shares an electron pair with an oxygen atom such that hydrogen acquires a duplet configuration in oxygen an octet. This results in the formation of two single covalent bonds.
Well, different scientists have different ways of expressing bond formation. Few of the molecules are described diagrammatically with the concept given by Lewis dot structure. Whereas some complex molecules are diagrammatically represented with separate explanations.
It is interesting to note that water molecules have totally different properties than individual atoms involving in bonds. The presence of electrons in an atom has a huge impact. Sharing a single electron totally changes the characteristics of the whole atom.
H2O A Compoud
Water has been used by man ever since it came into existence. Owing to its high stability, water was initially considered to be an element. Henry Cavendish, in 1781, proved that water is a compound made up of two elements: hydrogen and oxygen. He obtained water by burning hydrogen in air with the help of an electric spark. The conclusion made by Cavendish (about water) was later supported by Lavoisier.
Water breaks up into its constituent elements, viz. : oxygen and hydrogen when heated to a temperature of 2000°–3500°C or when an electric current is passed through it. But for this process to take place, water must contain a small amount of salt or acid in it. This process is called electrolysis.
The process of breaking down a compound, which is in a molten or a solution form, bypassing an electric current through it, is called electrolysis.
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