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

Key Concepts

Element: A substance where all atoms are the same. There are around 100 different elements, each with a unique symbol shown on the periodic table.
- Example: Magnesium (Mg), Sulfur (S)
- Definition: In an element, all atoms are identical.
- Symbols: Always start with a capital letter (e.g., Mg for Magnesium, S for Sulfur).
Compound: A substance formed when two or more different elements are chemically combined in fixed proportions.
- Example: Magnesium sulfide (MgS)
- Properties: Compounds usually have different properties from the elements they are made from.
- Separation: Requires a chemical reaction to separate the elements in a compound.
Mixture: Contains different elements or compounds that are not chemically combined.
- Example: A mixture of magnesium atoms, sulfur atoms, and magnesium sulfide.
- Separation: Can be separated using physical methods such as filtration, distillation, crystallization, or chromatography (to be covered in later lessons).
Molecule: Two or more atoms chemically combined. Molecules can consist of the same or different elements.
- Compounds as Molecules: Methane (CH₄), Water (H₂O), Ammonia (NH₃)
  - Methane: Carbon and hydrogen
  - Water: Hydrogen and oxygen
  - Ammonia: Nitrogen and hydrogen
- Elements as Molecules: Chlorine (Cl₂), Oxygen (O₂)
  - These are molecules but not compounds as they consist of the same type of atoms chemically combined.

The periodic table is essential for identifying symbols and properties of elements.
Physical separation techniques for mixtures will be explored in future videos.
For further practice, refer to the revision workbook available through the provided link.

This summary captures the essential definitions and distinctions between elements, compounds, mixtures, and molecules as discussed in the lecture.