Introduction to Chemical Bonds

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Introduction to Chemical Bonds

This lesson aligns with NGSS PS1.A

Introduction

When you look around you, you realise that things around us are made up of different atoms that have been joined together. This is known as chemical bonding. Chemical bonding is a natural phenomenon wherein atoms and molecules are attracted to each other, resulting in the formation of more stable chemical compounds. In chemical bonding, only valence electrons, which are electrons situated in the orbitals of an element's outermost energy level (valence shell), are involved. The three types of bonds are formed such as covalent bond, ionic bond, metallic bonds. In this article, we will learn about the formation of bonds, the Octet rule and Lewis structures of atoms.

How bonds are formed?

A chemical bond arises when atoms are bound together by attractive forces. This attraction occurs through the sharing of electrons between atoms or through the exchange of electrons between the participating atoms. The sharing or transfer of electrons occurs with the aim of achieving a filled outer energy level for the involved atoms, thereby enhancing their stability.

Consequently, electrons spend their time orbiting around both atoms involved in the bond. In the case of electron exchange, it denotes the transfer from one atom to another. In simpler terms, one atom gains an electron while the other loses one, establishing a balanced and more stable configuration for both atoms.

Octet Rule:

The octet rule is a guiding principle that states atoms tend to gain, lose, or share electrons to achieve a stable configuration with eight electrons in their outermost shell. This principle explains the tendency of atoms to form bonds and compounds, driven by the pursuit of a more stable state.

Importance of Valence Electrons in bond formation

These electrons, located in the outermost energy level or valence shell of an atom, are involved in interactions with other atoms. The number of valence electrons influences an atom's reactivity and its ability to form specific types of bonds.

For instance: in covalent bonding, atoms share valence electrons to achieve a more stable electron configuration.

In ionic bonding, valence electrons are transferred between atoms, resulting in the formation of positively and negatively charged ions.

Lewis Structure

A Lewis Structure is a simplified depiction of the distribution of valence shell electrons within a molecule. Its purpose is to illustrate the arrangement of electrons surrounding individual atoms within a molecule. Electrons are symbolized as "dots," and for bonding electrons, a line is utilized to represent the connection between the two atoms.

How to draw Lewis Structure:

Step 1: Calculate the total number of valence electrons.

Step 2: Establish the preliminary structure of the molecule.

Step 3: Allocate two valence electrons for each bond in the initial structure.

Step 4: Aim to fulfill the octets of the atoms by distributing the remaining valence electrons as nonbonding electrons.

First step involves computing the valence electrons in the molecule or ion. In the case of a neutral molecule, this entails adding the valence electrons of each atom. For charged molecules, one electron is added for each negative charge or subtracted for each positive charge.

Illustrative Example: Let's determine the valence electrons in the chlorate ([math]ClO_3^-[/math]) ion.

A chlorine atom (Group VIIA) has seven valence electrons, and each oxygen atom (Group VIA) has six valence electrons. Considering the -1 charge of the chlorate ion, it possesses one additional electron compared to a neutral ClO3 molecule, resulting in a total of 26 valence electrons.

[math]ClO_3^-[/math]: 7 + 3(6) + 1 = 26

The second step involves determining the atoms connected by covalent bonds, often indicated by the molecular formula. In the case of the chlorate ion, the suggested skeleton structure is derived from its formula.

In the third step, assuming the skeleton structure is held together by covalent bonds, the valence electrons are categorized into bonding and nonbonding electrons. Since two electrons form a covalent bond, the number of nonbonding electrons can be calculated by subtracting two electrons for each bond from the total valence electrons in the structure.

For instance, the chlorate ion's skeleton structure involves three covalent bonds, utilizing six of the 26 valence electrons as bonding electrons and leaving 20 as nonbonding electrons.

26 valence electrons = 6 bonding electrons + 20 nonbonding electrons

These nonbonding electrons are used to satisfy the octets of the atoms in the molecule. Each oxygen atom already contributes two electrons from the Cl-O covalent bond. As each oxygen atom requires six nonbonding electrons to fulfill its octet, 18 nonbonding electrons are utilized for the three oxygen atoms. This leaves one pair of nonbonding electrons to complete the octet of the central atom.

The fourth step is drawing the skeleton structure of the molecule. As a general guideline, the less electronegative element tends to be positioned at the center of the molecule.

Summary

Chemical bonding is a natural phenomenon wherein atoms and molecules are attracted to each other, resulting in the formation of more stable chemical compounds.
A chemical bond arises when atoms are bound together by attractive forces.
The octet rule is a guiding principle that states atoms tend to gain, lose, or share electrons to achieve a stable configuration with eight electrons in their outermost shell.
In a Lewis structure, electrons are symbolized as "dots," and for bonding electrons, a line is utilized to represent the connection between the two atoms.

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