The sharing of pair of electrons between two atoms is referred to as a covalent bond. Normally, each atom that is participating in the covalent bond formation, contributes equal number of electrons to form pair(s) of electrons. The pair of electrons shared between the atoms is also known as bond pair.

Lewis dot structures (or just Lewis structures) were developed around 1920 by pioneering chemist Gilbert Lewis, as a way of picturing chemical bonding in molecules. We draw Lewis structures to. Discover the bonding arrangement of atoms,; Discover whether there is any degeneracy of bonding (more on that later),; Figure out whether a given group of atoms might even bond together to form a.

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To generate the Lewis dot structure, you have to follow the given steps: Find the total count of valence electrons to molecules. In this step, add the total count of valence electrons from all the atoms in a bit. Find the required count of electrons needed to make the atoms complete.

The bond pair is strongly attracted by the nuclei of two atoms and thus by reducing the potential energy of them. This is the driving force of formation of covalent bond, which stabilizes the two atoms.

The distance between the nuclei of two atoms when their potential energy reaches a minima is also known as bond length. The forces of attraction between these two atoms are maximum at this point. However, the repulsion forces dominate over the attraction forces when these atoms are bring further closer together and thus by increasing the potential energy.

If two atoms share only one bond pair, that bond is referred to as a single bond. If two bond pairs are shared, that is known as a double bond. Likewise, a triple bond is formed when the atoms share three bond pairs.

A covalent bond is formed between two atoms when their electronegativity difference is less than 1.7 on Pauling's scale. Usually it is formed between two nonmetals.

Polarity of covalent bond: The bond pair is equally shared in between two atoms when the electronegativity difference between them is zero or nearer to zero. In this case, neither of the atoms gets excess of electron density and hence carry no charge. This is called non polar covalent bond.

However, when there is a considerable difference in the electronegativity, the bond pair is no longer shared equally between the atoms. It is shifted slightly towards the atom with higher electronegativity by creating partial negative charge (represented by δ-) over it. Whereas, the atom with less electronegativity gets partial positive charge (represented by δ+). This type of bond is also referred to as polar covalent bond.

Coordinate covalent bond: Some times, during the formation of covalent bond, the shared pair is entirely contributed by only one atom This is called as coordinate covalent bond or dative bond.

LEWIS DOT MODEL

To explain the formation of covalent bond, a simple qualitative model was developed by Gilbert Newton Lewis in 1916.

According to this model:

* Octet rule: The inert gas atoms with 8 electrons in their outer shell (also known as valence shell) are highly stable. The Helium atom with 2 electrons in its outer shell is also stable.

Hence every atom tries to get nearest inert gas configuration by sharing electrons. The bond formed due to sharing of electrons is otherwise known as a covalent bond.

* Only the electrons in the valence shell are contributed for sharing. The inner electrons, which are also known as core electrons do not participate in the bond formation.

* In the formation of covalent bond between two atoms, each atom contributes its valence electrons to form pair(s) of electrons, which in turn is/are shared by both of them.

Due to sharing of electrons, each atom gets nearest inert gas configuration.

Covalency : The number of electrons contributed by the atom of an element in the formation of covalent compound is known as covalency of that element.

In Lewis dot model, the electrons in the valence shell of the atom are shown as dots around it.

ILLUSTRATIONS OF LEWIS DOT STRUCTURES

1) H₂ molecule:

* The electronic configuration of hydrogen is 1s¹. It requires one electron to get the configuration of Helium.

* Therefore, during the formation of H₂ molecule, each hydrogen atom contributes one electron to form a pair of electrons. This in turn is shared between the two hydrogen atoms to form a covalent bond.

* Thus in H₂ molecule, each hydrogen atom gets its nearest inert gas: Helium's configuration, 1s².

* The covalency of hydrogen is 1.

* The Lewis dot structure for H₂ molecule is shown below. Note that each hydrogen gets two electrons after forming the bond. The bond between two hydrogen atoms can be shown as a line, which represents a bond pair of electrons.

Pokemon matching game d4s painted. Note: The bond between two hydrogen atoms is non polar since the electronegativity difference is zero.

2) Cl₂ molecule:

* The electronic configuration of Cl is [Ne]3s²3p⁵. There are 7 electrons in the outer shell.

* Therefore, in order to get the nearest inert gas: Argon's configuration, [Ne]3s²3p⁶, each chlorine atom contributes one electron for the bond formation and form a bond pair, which is shared between the two chlorine atoms.

* Thus Cl₂ molecule is formed with a covalent bond between two chlorine atoms.

* In Cl₂ molecule, each Cl atom gets 8 electrons in its outer shell. See the diagram below.

The bond pair is also shown as a line. The electron pairs which do not participate in the bonding are known as lone pairs. There are three such lone pairs on each of the chlorine atom.

* Hence the covalency of chlorine is 1.

* Remember that, in the Lewis dot structures, only the electrons in the valence shell are shown.

Note: The bond between two chlorine atoms is non polar since the electronegativity difference is zero.

3) Hydrogen chloride (HCl):

* The electronic configuration of hydrogen is 1s¹. It requires one electron to get the configuration of He.

* The electronic configuration of chlorine is [Ne]3s²3p⁵. It also requires one electron to get the octet configuration.

Lewis Structure Worksheet And Key

* Hence, in the formation of HCl molecule, the hydrogen and chlorine atoms contribute one electron each for the bond formation.

Note: The bond between hydrogen and chlorine atoms is considerably polar, since the electronegativity difference between them is 3.5 - 2.1 = 1.4. However they do not form ionic bond since the e.n. difference is less than 1.7.

The hydrogen atom gets partial positive charge, whereas the chlorine atom gets partial negative charge. However, they are not completely ionized.

4) Methane (CH₄):

* The electronic configuration of carbon is [He]2s²2p².

* The electronic configuration of hydrogen is 1s¹. Hence it contributes this electron to get the nearest inert gas, Helium's configuration.

* The carbon atom forms four covalent bonds by contributing four of its valence electrons. It forms 4 bonds with four hydrogen atoms. Thus it gets octet configuration.

* Covalency of carbon is 4.

* There are no lone pairs on carbon in methane.

Note: The electronegativity difference between carbon (e.n. = 2.5) and hydrogen (e.n. = 2.1) is not considerable. Serato dj

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