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Chemical Bonding

All known elements are arranged in the increasing order of their atomic number in the modern periodic table. In an atom, the outermost shell is known as valence shell and electrons placed in this shell are called as valence shell electrons. The valence shell electrons take part in the chemical bonding and chemical reactions with other atoms. All elements tend to get the octet configuration which makes them stable just like Nobel gases.

We know that the electronic configuration of Noble gases is ns2, np6 which is called as octet configuration. So how does an element get this stable configuration? There are two possible ways to get this configuration. One is either sharing their valence electrons with other elements or by the complete transfer of electrons to form ions. The sharing or transfer of electrons creates some attraction force between elements that is called as chemical bond. The formation of chemical bond completes the octet configuration of element and makes them stable in a molecule. The sharing of electrons between bonded atoms forms a covalent bond whereas complete transfer of electrons forms ionic bonds. Let’s discuss what chemical bond is and how different types of chemical bonds are formed between the elements.

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Electrovalent (ionic) Bonding

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When an atom donates one, two or three electrons from its valence shell to another atom, which has the ability to accept these electrons, it is known as electrovalency. As a result of electrovalency, both these atoms achieve the structure of an inert gas. Electrovalent bond is the attractive force between the oppositely charged ions, which comes into existence by the transference of electrons.

Electrovalent compounds are compounds formed by completed transfer of electrons from a metallic atom to a non-metallic atom resulting in the formation of cation and anion.

When the combining atoms have 4, 5, 6, or 7 electrons in the outermost or valence shell, they cannot donate electrons. Instead, they mutually share electrons in order to complete their octet in the outermost orbit or shell. Such a type of valency is referred to as covalency and the bond created between such atoms is called a covalent bond. The compounds so formed are called covalent compounds or molecular compounds. → Read More

Properties of Electrovalent and Covalent Compounds

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Comparison of Properties of Electrovalent and Covalent Compounds.

Polar and Non-polar Molecules

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When compounds are formed from elements whose atoms have different electronegativities, the electrons forming the bonds will have a tendency to be attracted closer to the more electronegative element. In such instances covalent molecules develop some ionic character and are called polar molecules. As a result of polarity, a small negative charge (d-) appears on the more electronegative atom and a small electropositive charge (d+) appears on the less electronegative atom.

Oxidation and Reduction

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In most of the combinations discussed above, it can be seen that many reactions involve transfer of electrons from one species to another. These electron transfer reactions can also be studied under another category of reactions called the oxidation and reduction reactions.

Oxidation

"Oxidation is the loss of electrons from an atom."

Oxidation reactions
Sodium atom loses an electron and gets converted to a positively charged sodium ion. Sodium atom is oxidized to sodium ion.


Reduction

"Reduction is the process in which an atom gains one or more electrons."

Reduction reactions
A chlorine atom will gain an electron to become a chloride ion.

Hydronium and Ammonium Ions

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The hydronium ion is a hydrogen ion in association with a molecule of water. In a water molecule, the oxygen atom has two pairs of unshared electrons in its outermost shell. The hydrogen ion does not have any electron in its valence shell. Hence it shares a pair of electrons from the oxygen atom by means of co-ordinate co-valency to form a hydronium.

Types of Chemical Bonding

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As a matter of convenience we usually divide chemical bonds into different types. There are two major classes of bonding
  1. Ionic bonding which results from electrostatic interaction among ions; and can be formed by the transfer of one or more electrons from one atom or group of atoms to another.
  2. Covalent bonding which results from sharing one or more electron pairs between two atoms.

These represent two extremes and all bonds have at least some degree of both ionic and covalent character. Compounds in which the bonding is predominantly ionic are called ionic compounds, and those in which the bonding is predominantly covalent are called covalent compounds.

In addition attractive interactions between atoms of different molecules can give rise to weak bonds of the following types.

  1. Hydrogen bonds
  2. Van der waals interaction

Bonding between metal ions is known as metallic bonding.

An important characteristic of chemical bonding is the maximum number of bonds that a given atom can make. The number of covalent bonds that an atom can form is called its valence. The number of possible bonds is limited only by the number of atoms that can touch each other simultaneously.

Number of valence pairs
Bond angles
Examples
2
180o BeF2, BeH2
3 120o BCl3
4 109.5o
CH4, CCl4, GeF4


More topics in Chemical Bonding
Coordinate Covalent Bond Intermolecular Forces
Bond Energy Ionic Bonding
Covalent Bonding Metallic Bonding
Hydrogen Bonding Dispersion Forces
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