Summary of Pure Substances

Key Concepts in Pure Substances

• Introduction to Matter:

• Elements make up the universe.

• Distinction between gases, liquids, solids.

• Example: Table salt (sodium chloride) as a pure substance.

Pure Substances:

• Made of one type of atom or particle, homogenous.

• Types of pure substances: elements and compounds.

Elements:

• Comprised of the same type of atom (e.g., aluminum, gold).

• All known elements listed on the periodic table.

• Molecule Definition:

• Formed when two or more atoms combine chemically.

• Diatomic Molecules:

• Molecules with two identical atoms (e.g., O2, H2).

Compounds:

• Formed from atoms of two or more different elements (e.g., CO2, H2O).

• Fixed ratio of atoms unless affected by a chemical reaction.

Testing for Pure Substances:

• Few elements or compounds occur in pure form.

• Ways to test purity:

• State at room temperature (solid, liquid, gas).

• Conductivity, magnetism, solubility, buoyancy.

• Melting and boiling points (e.g., pure water at 100°C).

Molecules Overview:

• Pure substances are made of molecules (homogenous composition).

• Types:

• Single element molecules.

• Compound molecules made of different elements.

Summary:

• Pure substances consist of one particle type.

• Two types: elements and compounds.

• Understanding molecules is crucial for learning about compounds.