5.2 Chemical Bonds

This topic explains what chemical bonds are, how they form, and introduces the concepts of electropositivity and electronegativity.

Definition

Chemical bonds are the forces of attraction that hold atoms together in substances.

Simple explanation: A chemical bond is the "glue" that holds atoms together.

Main Idea

Atoms combine to form various types of substances. But what holds them together? Fundamentally, some forces of attraction hold atoms together in substances. These forces are called chemical bonds.

Basically, the forces of attraction that lead to chemical bonding between atoms are electrical in nature.

Simple explanation: Chemical bonds are electrical attractions between atoms — positive and negative charges attract each other.

Core Concept

Why Atoms Form Bonds

The electronic structure of an atom helps us understand how atoms are held together to form substances.

Atoms other than the noble gases have a tendency to react with other elements. These elements are reactive because they tend to gain stability by losing or gaining electrons.

When atoms gain or lose electrons, they acquire the configuration of the next noble gas element.

Simple explanation: Atoms form bonds to become stable like noble gases.

Electropositivity and Electronegativity

The book introduces two key terms:

Electropositivity: The tendency of metal atoms to lose electrons is called electropositivity.

Electronegativity: The tendency of non-metal atoms to gain electrons is called electronegativity.

• Metals are electropositive elements.
• Non-metals are electronegative elements.

Simple explanation: Metals like to give away electrons; non-metals like to take electrons.

Sharing Electrons

Atoms can also acquire the configuration of the next noble gas element by sharing electrons.

Simple explanation: Some atoms share electrons instead of losing or gaining them completely.

Detailed Explanation

The Nature of Chemical Bonds

Chemical bonds are electrical in nature:

• Positive charges attract negative charges.
• Nuclei (positive) attract electrons (negative).
• This attraction holds atoms together.

Simple explanation: Chemical bonds are just electrical attractions between positive nuclei and negative electrons.

Electropositive Elements (Metals)

• All metal atoms lose electrons from their outermost shell to become stable.
• They become positively charged (cations).
• They have low ionization energy and low electronegativity, allowing them to easily lose electrons.
• Therefore, they can form positive ions by losing electrons.

Examples:

Na → Na⁺ + e^-

Mg → Mg²⁺ + 2e^-

Simple explanation: Metals lose electrons to become positive ions.

Electronegative Elements (Non-Metals)

• All non-metal atoms gain electrons to become stable.
• They become negatively charged (anions).
• They have high electronegativity and high electron affinity.
• So they can easily form negative ions by gaining electrons.

Examples:

F + e^- → F^-

O + 2e^- → O^2-

Simple explanation: Non-metals gain electrons to become negative ions.

Summary Table

Intermediate Level

Why Chemical Bonds Are Electrical in Nature

• Attraction between positive nuclei and negative electrons.
• Attraction between positive and negative ions.

The electrons in an atom are negatively charged. The nucleus is positively charged. When atoms come close together, these charges interact, forming bonds.

Types of Bonding (Preview)

The book mentions three types of bonding:

• Ionic bonding — between metals and non-metals (transfer of electrons).
• Covalent bonding — between non-metals (sharing of electrons).
• Metallic bonding — between metal atoms (sea of delocalized electrons).

Detailed explanation of each type comes in later sections.

Why Metals Lose Electrons Easily

• Have low ionization energy (easy to remove electrons).
• Have low electronegativity (don't attract electrons strongly).
• Have 1–3 valence electrons (easier to lose them than gain 7–5 electrons).

So they lose electrons and form positive ions.

Why Non-Metals Gain Electrons Easily

• Have high ionization energy (hard to remove electrons).
• Have high electronegativity (attract electrons strongly).
• Have 5–7 valence electrons (easier to gain 1–3 electrons than lose 5–7).

So they gain electrons and form negative ions.

Sharing Electrons — A Third Way

Some atoms (especially non-metals) can achieve stability by sharing electrons rather than completely losing or gaining them.

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: When atoms share electrons, both become stable without forming full ions.

Important Points

• - Chemical bonds: forces of attraction that hold atoms together.
• - Nature: electrical (attraction between positive and negative charges).
• - Electropositivity: tendency of metal atoms to lose electrons.
• - Electronegativity: tendency of non-metal atoms to gain electrons.
• - Metals are electropositive → lose electrons → form cations.
• - Non-metals are electronegative → gain electrons → form anions.
• - Atoms can also achieve stability by sharing electrons.
• - Atoms gain or lose electrons to achieve the configuration of the next noble gas.

Remember

• - Chemical bond = force of attraction holding atoms together.
• - Nature: electrical (positive–negative attraction).
• - Electropositivity: metals lose electrons → form cations.
• - Electronegativity: non-metals gain electrons → form anions.
• - Na → Na⁺ (metal loses electron).
• - F → F⁻ (non-metal gains electron).
• - Sharing electrons is another way to become stable.
• - Atoms gain/lose electrons to achieve noble gas configuration.

Common Mistakes

• 1. Thinking chemical bonds are physical "glue." They are electrical attractions.
• 2. Confusing electropositivity and electronegativity. Electropositivity = losing electrons (metals); electronegativity = gaining electrons (non-metals).
• 3. Thinking all atoms gain electrons. Metals lose electrons; non-metals gain electrons.
• 4. Forgetting the role of noble gas configuration. Atoms react to achieve the configuration of the nearest noble gas.
• 5. Thinking chemical bonds only involve ions. Atoms can also form bonds by sharing electrons.
• 6. Confusing electronegativity with electron affinity. Electronegativity is a general tendency; electron affinity is a specific energy measurement.

Quick Revision

• Chemical bonds: forces of attraction that hold atoms together.
• Nature: electrical in nature.
• Electropositivity: tendency of metal atoms to lose electrons.
• Electronegativity: tendency of non-metal atoms to gain electrons.
• Metals: electropositive; lose electrons; form positive ions (cations).
• Non-metals: electronegative; gain electrons; form negative ions (anions).
• Atoms can also achieve noble gas configuration by sharing electrons.
• Examples:
• Na → Na⁺ + e⁻
• Mg → Mg²⁺ + 2e⁻
• F + e⁻ → F⁻
• O + 2e⁻ → O²⁻

60-Second Revision

• Chemical bond = force of attraction holding atoms together.
• Nature: electrical.
• Electropositivity: metals lose electrons → cations.
• Electronegativity: non-metals gain electrons → anions.
• Na → Na⁺; F → F⁻.
• Atoms react to achieve noble gas configuration.
• Warning: electropositivity is not the same as electronegativity.