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

Key Concepts

• Element:

  • Around 100 different elements, represented in the periodic table.
  • Each element has a unique symbol; starts with a capital letter (e.g., Magnesium: Mg, Sulfur: S).
  • Definition: All atoms in an element are the same.
  • Examples: Magnesium (Mg), Sulfur (S).

• Compound:

  • Formed when two or more different elements are chemically combined in fixed proportions.
  • Example: Magnesium Sulfide (MgS) - 1 Magnesium atom for every 1 Sulfur atom.
  • Properties of compounds differ from constituent elements.
  • Separation of elements in a compound requires a chemical reaction.

• Mixture:

  • Contains different elements or compounds not chemically combined.
  • Example: Mixture of Mg atoms, S atoms, and MgS.
  • Can be separated using physical techniques like filtration, distillation, crystallization, chromatography.

• Molecule:

  • Defined as any elements chemically combined.
  • Can be a compound (different elements combined) or not (same element combined).
  • Examples of molecules that are compounds: Methane (CH₄), Water (H₂O), Ammonia (NH₃).
  • Examples of molecules that are not compounds: Chlorine (Cl₂, two Chlorine atoms), Oxygen (O₂, two Oxygen atoms).

Important Definitions

• Element: A substance made of only one type of atom.
• Compound: A substance formed by chemical combination of two or more elements in a fixed ratio.
• Mixture: A combination of different elements or compounds that are not chemically bonded.
• Molecule: Two or more atoms chemically bonded, can be of the same or different elements.

Study Tips

• Familiarize yourself with the periodic table and symbols for elements.
• Understand the distinction between elements, compounds, and mixtures.
• Learn the definition and examples of molecules, and how they relate to compounds.
• Practice physical separation techniques for mixtures through examples in further lessons.

Additional Resources

• Refer to the revision workbook for practice questions on these topics.

This summary captures the essential points of the lecture and provides a reference for understanding the basic chemistry concepts of elements, compounds, mixtures, and molecules.