molecules

toms from different elements bonded togethA molecule is the smallest unit of a chemical compound that can exist independently and retains the chemical properties of that compound. A molecule is made up of two or more atoms that are chemically bonded together.

Classification of Molecules Based on the Number of Atoms:

1. Monoatomic Molecules:
   These molecules consist of only one atom of the element. They are most often the noble gases, which exist naturally as single atoms.

   • Examples:

     • He (Helium)

     • Ne (Neon)

     • Ar (Argon)

     • Kr (Krypton)

     • Xe (Xenon)

     • Rn (Radon)

2. Diatomic Molecules:
   These molecules consist of two atoms of the same element chemically bonded together.

   • Examples:

     • O₂ (Oxygen)

     • H₂ (Hydrogen)

     • F₂ (Fluorine)

     • Cl₂ (Chlorine)

     • I₂ (Iodine)

   Note: Some elements naturally form diatomic molecules when they exist in their elemental state.

3. Polyatomic Molecules:
   These molecules consist of more than two atoms of the same element bonded together. They are usually formed by elements that have multiple atoms in their molecular form.

   • Examples:

     • O₃ (Ozone)

     • P₄ (Phosphorus)

     • S₈ (Sulfur)

Molecules of Compounds

A molecule of a compound is made up of two or more atoms of different elements chemically bonded together. Unlike molecules of elements (which are made of atoms of the same element), molecules of compounds contain atoms from different elements.

• Examples of compound molecules:

  • H₂O (Water) — made of 2 hydrogen atoms and 1 oxygen atom.

  • NH₃ (Ammonia) — made of 1 nitrogen atom and 3 hydrogen atoms.

  • CO₂ (Carbon dioxide) — made of 1 carbon atom and 2 oxygen atoms.

Exercise 2.3

1. What is a molecule?
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Notes on Molecules and Their Types

What is a Molecule?

• A molecule is the smallest unit of a chemical substance that can exist independently. It consists of two or more atoms that are chemically bonded together.

• Molecules retain the chemical properties of the substance they form.

Types of Molecules

1. Monoatomic Molecules

   • Definition: Molecules consisting of a single atom of an element.

   • Examples:

     • He (Helium)

     • Ne (Neon)

     • Ar (Argon)

     • Kr (Krypton)

     • Xe (Xenon)

     • Rn (Radon)

   • Note: These are often the noble gases that exist as individual atoms in nature.

2. Diatomic Molecules

   • Definition: Molecules made up of two atoms of the same element chemically bonded together.

   • Examples:

     • O₂ (Oxygen)

     • H₂ (Hydrogen)

     • F₂ (Fluorine)

     • Cl₂ (Chlorine)

     • I₂ (Iodine)

   • Note: These molecules form naturally because certain elements are more stable when paired with another atom of the same element.

3. Polyatomic Molecules

   • Definition: Molecules containing more than two atoms of the same element.

   • Examples:

     • O₃ (Ozone)

     • P₄ (Phosphorus)

     • S₈ (Sulfur)

   • Note: These molecules often form when atoms bond together in specific patterns to achieve stability.

Molecules of Compounds

• A molecule of a compound is made of two or more atoms of different elements chemically bonded together.

• Examples of compound molecules:

  • H₂O (Water) — 2 hydrogen atoms and 1 oxygen atom.

  • NH₃ (Ammonia) — 1 nitrogen atom and 3 hydrogen atoms.

  • CO₂ (Carbon dioxide) — 1 carbon atom and 2 oxygen atoms.

Summary

• Molecules can be made of atoms of the same element (monoatomic, diatomic, polyatomic) or different elements (compounds).

• Monoatomic molecules consist of one atom.

• Diatomic molecules contain two atoms of the same element.

• Polyatomic molecules contain more than two atoms of the same element.

• Compounds are molecules made of aer.