Chemistry Review on Matter and Molecules

Study Notes

Chemistry is the study of matter
Matter is anything that takes up space
Matter can be categorized as either pure substances or mixtures
- Pure substances have a constant composition
  - Elements are pure substances that cannot be broken down into simpler units (e.g., Hydrogen (H), Calcium (Ca))
  - Compounds are pure substances that contain two or more different elements in a fixed proportion (e.g., Water (H₂O), Carbon dioxide (CO₂), Sugar (C₆H₁₂O₆))
- Mixtures have a variable composition
  - Solutions are homogeneous mixtures (e.g., salt in water). Only one type of substance is visible
  - Mechanical mixtures are heterogeneous mixtures (e.g., oil and water) where more than one substance is visible

Molecules are formed when two or more atoms join together (e.g., O₂ - oxygen molecule, NH₃ - ammonia molecule, H₂O - water molecule)

Homogeneous matter contains only one type of substance (e.g., salt in milk, oil)
Heterogeneous matter contains more than one type of substance (e.g., mixtures of salt and pepper or oil and water)

Properties of matter are used to identify different types of matter
Two types of properties exist: physical and chemical
Physical properties can be observed or measured without changing the substance (e.g., temperature, colour, volume, texture, mass, taste, clarity, hardness)
Chemical properties describe how a substance reacts with another substance to produce a new substance (e.g., flammability, reactivity, corrosiveness)

Characteristic physical properties are properties unique to a particular substance that distinguish it from other substances.
- Example: Boiling point
  - Boiling point of a substance is usually unique. (e.g., water boils at 100°C)

Chemical properties describe how a substance reacts with another substance during a chemical reaction to form a new substance (e.g., Oxygen burns something, reacting to form rust, reacting with Chlorine to form salt)

Physical change is a change in the state of matter, but no new substance is formed (e.g., melting, dissolving, freezing)
Chemical change is a change in matter where a new substance is formed with different properties than the original substance(s). (e.g., burning, rusting)