Physical and Chemical Properties

Every material has properties that describe it. Scientists sort these properties into two groups: physical properties and chemical properties. Knowing the difference helps us identify, classify, and choose materials for specific purposes.

Physical Properties

A physical property can be observed or measured without changing what the substance is made of. The substance stays the same substance after you observe it.

• Color — the color of a material as seen by the eye.
• Mass — how much matter is in an object, measured with a scale.
• Volume — how much space an object takes up.
• Density — how much mass is packed into a given volume.
• Melting point — the temperature at which a solid turns to liquid.
• Boiling point — the temperature at which a liquid turns to gas.
• Hardness — how resistant a material is to being scratched.
• Texture — how a surface feels (smooth, rough, grainy).

Chemical Properties

A chemical property describes how a substance reacts or transforms into a different substance. You can only observe a chemical property when a chemical change actually happens.

• Flammability — the ability of a substance to burn in the presence of oxygen.
• Reactivity with acid — how a substance responds when it contacts an acid.
• Ability to rust — iron and steel react with oxygen and water to form rust (iron oxide).
• Toxicity — the ability of a substance to be harmful or poisonous to living things.

Physical Changes vs Chemical Changes

• Physical change — no new substance is formed. Example: melting ice, cutting paper, bending metal.
• Chemical change — a new substance is formed. Example: burning wood, rusting iron, cooking an egg.
• Key question: Does a new substance form? Yes = chemical change. No = physical change.