In this lesson, we will explore the building blocks of matter: atoms. All substances around us are made up of these tiny units. Atoms can join together to form molecules, which can exist in different states, such as solids, liquids, or gases. The forces that hold atoms together in a molecule are known as chemical bonds. We will discuss how to find the number of valence electrons in an atom using the Periodic Table and why noble gas configurations are important for stability.

We will learn about the octet and duplet rules, which explain how elements achieve stability by having a certain number of electrons in their outer shell. We will also cover how elements form bonds, including ionic and covalent bonds.

Key topics include:

• How to identify valence electrons.
• The significance of noble gases.
• The octet and duplet rules.
• How elements gain stability.
• The formation of cations (positive ions) from metals and anions (negative ions) from non-metals.
• Characteristics of ionic bonds and ionic compounds.
• Formation of covalent bonds between non-metals, including single, double, and triple bonds.
• Drawing electron cross and dot structures for simple covalent molecules.

By the end of this lesson, you’ll have a better understanding of how atoms bond to create the matter we see every day.

CHEMICAL BOND

In a substance, atoms are held together by forces during bond formation. The octet rule explains how atoms achieve a stable configuration with eight electrons in their outer shell by sharing, losing, or gaining electrons. For lighter elements like hydrogen and helium, which only have two electrons, this concept is referred to as the duplet rule.

When bonds form between ions, it is due to the electrostatic attraction between positively and negatively charged ions. In contrast, when similar atoms or atoms with similar electronegativities bond, they do so by sharing electrons. This sharing can be mutual or one-sided. As two atoms approach each other, both attractive and repulsive forces come into play. A chemical bond forms when the attractive forces outweigh the repulsive forces, resulting in a lower energy state and the formation of a molecule. If the repulsive forces dominate, no bond will form, and the energy of the system will increase.

There are four main types of chemical bonds based on how valence electrons interact: ionic bonds, covalent bonds, dative covalent bonds, and metallic bonds.

Ionic Bonds

Ionic bonds occur primarily between metals (like those in Groups 1 and 2) and non-metals (like those in Groups 15 to 17). Metals tend to lose their valence electrons, becoming positively charged ions, while non-metals gain electrons, becoming negatively charged ions. For example, in the formation of sodium chloride (NaCl), sodium (with one valence electron) loses that electron to chlorine (which has seven valence electrons). As a result, sodium becomes a Na⁺ ion, while chlorine becomes a Cl⁻ ion. This transfer of electrons allows both elements to achieve a stable electronic configuration similar to that of noble gases. The electrostatic attraction between these oppositely charged ions forms a strong ionic bond, resulting in the creation of ionic compounds. Notably, only the valence electrons participate in this bonding process, and heat is often released during the reaction.

Covalent Bond

When elements from Groups 13 to 17 react, they form covalent bonds by mutually sharing their valence electrons. This sharing creates a covalent bond, which is characterized by energy changes that occur during the process. As two atoms come close to each other, attractive forces develop between the electrons of one atom and the nucleus of the other. At the same time, repulsive forces arise between the electrons and nuclei of both atoms. A chemical bond is formed when the attractive forces become stronger than the repulsive forces, allowing the atoms to stabilize their energy.

Common examples of covalent bonding include the formation of gases like hydrogen, chlorine, nitrogen, and oxygen.

Types of Covalent Bonds

Covalent bonds can be classified based on the number of shared electron pairs:

1. Single Covalent Bond: This occurs when one electron from each bonded atom pairs up, forming a single bond. This is represented by a line between the two atoms in molecular diagrams. Examples include hydrogen (H₂), chlorine (Cl₂), hydrochloric acid (HCl), and methane (CH₄).
2. Double Covalent Bond: In this case, each atom shares two electrons, resulting in two shared pairs. This bond is indicated by a double line between the atoms. Examples include oxygen gas (O₂) and ethene (C₂H₄).
3. Triple Covalent Bond: This bond forms when each atom contributes three electrons, creating three shared pairs. It is represented by three lines between the atoms. Examples include nitrogen gas (N₂) and ethyne (C₂H₂).

Through this mutual sharing of electrons, each atom involved in the covalent bond achieves a more stable electronic configuration.

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