1) Classifying Matter

• Two principle ways of classifying matter are according to its physical state and according to its composition.
• The three main states of matter are solid, liquid, and gas.
• A gas has no fixed volume or shape; it conforms to the shape and volume of its container; it can be compressed or it can be expanded to fill its container.
• A liquid has a distinct volume but an indefinite shape; its shape conforms to the shape of its container.
• A solid has a definite shape and a definite volume.
• Neither liquids nor solids can be compressed to any appreciable extent.
• Molecules in a gas move freely at high speeds.
• Molecules in a liquid are closer together but move rapidly allowing the liquid to flow.
• Molecules in a solid are tightly packed and vibrate slightly in fixed positions.
• A substance is matter that has distinct properties and a composition that does not vary from sample to sample.
• Substances are either elements or compounds.
• Elements cannot be decomposed into smaller components; they are composed of one kind of atom.
• Compounds are composed of two or more elements of the same or different kinds of atoms.
• A mixture is a combination of two or more substances in which each retains its chemical identity.
• Most elements can interact to form compounds.
• The law of constant composition or law of definite proportions states that the elemental composition of a pure compound is always the same.
• Mixtures come in two forms: heterogeneous or homogeneous.
• Heterogeneous mixtures vary in texture and are not uniform throughout.
• Homogeneous mixtures are uniform throughout and are also called solutions.