5.3 Types of Bonds

This topic introduces the two main types of chemical bonds — ionic bonds and covalent bonds — based on how atoms lose, gain, or share electrons.

Definition

Chemical bonds are the forces of attraction that hold atoms together. Depending on the tendency of an atom to lose, gain, or share electrons, there are two main types of bonds:

• Ionic bonds
• Covalent bonds

Simple explanation: Atoms can either give away electrons completely (ionic bonds) or share them (covalent bonds).

Main Idea

Atoms form bonds to achieve a stable electron configuration like noble gases.

• Metals tend to lose electrons → form cations.
• Non-metals tend to gain electrons → form anions.
• When a metal and a non-metal react, the metal gives electrons to the non-metal → ionic bond.
• When two non-metals react, they share electrons → covalent bond.

Simple explanation: Ionic bonds = giving and taking electrons; covalent bonds = sharing electrons.

Core Concept

Detailed Explanation

Ionic Bonds

• One atom loses electrons to form a cation.
• The other atom gains those electrons to form an anion.

The bond is the strong electrostatic attraction between the oppositely charged ions.

Example 5.1: Formation of Na and Mg cations

Describe the formation of Na and Mg cations.

• Sodium belongs to Group IA. It has only one electron in the valence shell. The sodium atom loses its valence electron and is left with an octet.
• Magnesium belongs to Group IIA. It has two valence electrons. A magnesium atom loses these electrons to achieve noble gas configuration.

Solution:

(a) Formation of Na⁺ ion:

Na(1s² 2s² 2p⁶ 3s¹) -e^-→ Na⁺(1s² 2s² 2p⁶)

You can also represent this by electron dot structure.

(b) Formation of Mg²⁺ ion:

Mg(1s² 2s² 2p⁶ 3s²) -2e^-→ Mg²⁺(1s² 2s² 2p⁶)

You can also represent this by electron dot structure.

Covalent Bonds

Covalent bonds are formed when two atoms share one or more pairs of electrons.

This usually happens between non-metal atoms because neither atom wants to lose or gain electrons completely.

Example: Two hydrogen atoms share electrons to form H₂.

Each H atom contributes 1 electron to the shared pair. Both atoms achieve the duplet configuration of helium.

Simple explanation: In a covalent bond, atoms share electrons so both become stable.

Summary of Bond Types

Intermediate Level

Ionic Bond Formation — In Detail

Ionic bonds form between metals and non-metals.

• Metal atom loses electrons → forms cation.
• Non-metal atom gains those electrons → forms anion.
• Cations and anions attract each other → ionic bond.

Example: Sodium chloride (NaCl)

Na → Na⁺ + e^-

Cl + e^- → Cl^-

Na⁺ + Cl^- → NaCl

Simple explanation: Sodium gives an electron to chlorine; the resulting ions stick together.

Covalent Bond Formation — In Detail

Covalent bonds form between non-metals.

• Two atoms come close together.
• Each contributes one or more electrons to a shared pair.
• Both atoms achieve a stable configuration (octet or duplet).

Example: Hydrogen (H₂)

H · + · H → H:H

Each H atom shares 1 electron. Both achieve the duplet configuration of helium.

Example: Chlorine (Cl₂)

Cl · + · Cl → Cl:Cl

Each Cl atom shares 1 electron. Both achieve the octet configuration of argon.

Simple explanation: Two non-metals share electrons so both become stable.

Key Difference

Important Points

• - Two main types of bonds: ionic and covalent.
• - Ionic bonds: formed by transfer of electrons between metals and non-metals.
• - Covalent bonds: formed by sharing of electrons between non-metals.
• - Metals lose electrons → form cations.
• - Non-metals gain electrons → form anions.
• - Ionic bond: strong electrostatic attraction between oppositely charged ions.
• - Covalent bond: strong electrostatic attraction between shared electrons and two nuclei.
• - Examples:
• - Ionic: NaCl, MgO
• - Covalent: H₂, Cl₂, H₂O

Remember

• - Ionic bond = transfer of electrons (metal + non-metal).
• - Covalent bond = sharing of electrons (non-metal + non-metal).
• - Na → Na⁺; Cl → Cl⁻ → NaCl (ionic).
• - H + H → H₂ (covalent).
• - Ionic bonds form between metals and non-metals.
• - Covalent bonds form between non-metals.

Common Mistakes

• 1. Thinking all bonds involve sharing. Ionic bonds involve transfer, not sharing.
• 2. Thinking covalent bonds form between metals. Covalent bonds form between non-metals.
• 3. Confusing cations and anions. Cations are positive; anions are negative.
• 4. Thinking ionic bonds are weaker than covalent bonds. Both are strong, but in different ways.
• 5. Thinking H₂ has an ionic bond. H₂ has a covalent bond (sharing).
• 6. Forgetting that atoms form bonds to achieve noble gas configuration. This is the driving force.

Quick Revision

• Types of bonds:
• Examples:
• Ionic: NaCl (Na⁺ + Cl⁻), MgO (Mg²⁺ + O²⁻)
• Covalent: H₂, Cl₂, H₂O
• Metals lose electrons → form cations.
• Non-metals gain electrons → form anions.
• Both bond types form to achieve noble gas configuration.

60-Second Revision

• Two types of bonds: ionic and covalent.
• Ionic = transfer; metal + non-metal; NaCl.
• Covalent = sharing; non-metal + non-metal; H₂.
• Na → Na⁺; Cl → Cl⁻ → NaCl (ionic).
• H + H → H₂ (covalent).
• Warning: ionic bonds involve transfer, not sharing.