Free Science Lessons: Introduction to Elements, Compounds, Mixtures, and Molecules

Overview

• Understanding the concepts of elements, compounds, mixtures, and molecules is crucial in chemistry.
• The periodic table showcases around 100 different elements.

Elements

• Definition: An element consists of only one type of atom.
• Each element is represented by a unique symbol on the periodic table.
  • Example: Magnesium (Mg), Sulfur (S).
• Every element's symbol starts with a capital letter, followed by a lowercase letter if applicable.

Compounds

• Formed when two or more different elements are chemically combined in fixed proportions.
  • Example: Magnesium Sulfide (MgS) is composed of one Mg atom and one S atom.
• Properties: Compounds have distinct properties different from their constituent elements.
  • Example: Magnesium is shiny, Sulfur is a yellow solid, but Magnesium Sulfide forms white crystals.
• Separation requires a chemical reaction.

Mixtures

• Composed of different elements or compounds that are not chemically combined.
  • Example: A mixture of Mg atoms, S atoms, and MgS.
• Can be separated using physical methods (e.g., filtration, distillation, crystallization, chromatography).

Molecules

• Molecules consist of any elements chemically combined, including the same element.
  • Examples of molecules: Methane (CH₄), Water (H₂O), Ammonia (NH₃).
• Some molecules are also compounds because they contain different elements.
  • Methane: Carbon and Hydrogen
  • Water: Hydrogen and Oxygen
  • Ammonia: Nitrogen and Hydrogen
• Some molecules are not compounds but elements.
  • Chlorine molecule: Two Cl atoms
  • Oxygen molecule: Two O atoms

Conclusion

• Understanding these definitions and examples is essential for mastering basic chemistry concepts.
• Explore further through the revision workbook linked in the lesson.