Free Science Lessons: Understanding Elements, Compounds, Mixtures, and Molecules

Key Concepts

• Element

  • Definition: In an element, all of the atoms are the same.
  • Periodic Table: Contains around 100 different elements.
  • Examples: Magnesium (Mg) and Sulfur (S) are elements.
  • Characteristics: Each element has a unique symbol starting with a capital letter.

• Compound

  • Definition: Compounds consist of two or more different elements chemically combined in fixed proportions.
  • Example: Magnesium sulfide (MgS), where one atom of magnesium combines with one atom of sulfur.
  • Properties: Compounds usually have different properties from the elements they are made from.
  • Separation: Requires a chemical reaction to separate into elements.

• Mixture

  • Definition: Contains different elements or compounds not chemically combined.
  • Examples: A mixture might include magnesium atoms, sulfur atoms, and magnesium sulfide.
  • Separation: Can be separated by physical techniques like filtration, distillation, crystallization, or chromatography.

• Molecule

  • Definition: Comprises any elements chemically combined, including the same element.
  • Examples of Compounds: Methane (CH₄), Water (H₂O), Ammonia (NH₃) contain different elements.
  • Molecules as Elements: Chlorine (Cl₂) and Oxygen (O₂) consist of chemically combined same elements.

Additional Resources

• Revision Workbook: More questions on this topic are available in the revision workbook.

Important Points

• Understand and memorize the definitions of elements, compounds, mixtures, and molecules.
• Recognize the differences between chemical and physical separation processes.
• Note the properties and proportions of elements in compounds.