Section 1: Composition of Matter

• Pure Substances

  • Each material has its own properties. The properties of materials can be used to classify them into general categories.

  • Materials are made of a pure substance or a mixture of substances.

  • Substance: a type of matter with a fixed composition.

    • A substance can be either an element or a compound.

  • All substances are built from atoms.

  • Element: If all the atoms in a substance have the same identity

    • About 90 elements are found on Earth.

  • Compound: a substance in which the atoms of two or more elements are combined in a fixed proportion.

    • Compounds usually look different from the elements in them.

• Mixtures

  • Unlike compounds, mixtures do not always contain the same proportions of the substances that make them up.

  • Heterogeneous Mixture: A mixture in which different materials can be distinguished easily

    • Most of the substances you come in contact with every day are heterogeneous mixtures

    • Heterogeneous mixtures can be hard to detect.

  • Homogeneous Mixture: contains two or more gaseous, liquid, or solid substances blended evenly throughout.

    • Another name for homogeneous mixtures like vinegar and a cold soft drink is solution.

  • Solution: a homogeneous mixture of particles so small that they cannot be seen with a microscope and will never settle to the bottom of their container.

  • Milk is an example of a specific kind of mixture called a colloid.

    • Colloid: a type of mixture with particles that are larger than those in solutions but not heavy enough to settle out.

  • Fog is a colloid composed of water droplets suspended in air.

  • One way to distinguish a colloid from a solution is by its appearance.

    • You can tell for certain if a liquid is a colloid by passing a beam of light through it

  • Tyndall Effect: The scattering of light by colloidal particles

  • Some mixtures are neither solutions nor colloids.

  • Suspension: a heterogeneous mixture containing a liquid in which visible particles settle.

Section 2: Properties of Matter

• Physical Property: Any characteristic of a material that you can observe without changing the identity of the substances that make up the material.

  • You can measure some physical properties.

  • Some physical properties describe the behavior of a material or a substance.

  • Every substance has a specific combination of physical properties that make it useful for certain tasks.

  • Physical property can be used to separate substances in a mixture.

• Physical Change: A change in size, shape, or state of matter

  • These changes might involve energy changes, but the kind of substance—the identity of the element or compound—does not change.

  • Because all substances have distinct properties like densities, specific heats, and boiling and melting points, which are constant, these properties can be used to help identify them when a particular mixture contains substances which are not yet identified.

  • Color changes can accompany a physical change, too.

  • Distillation: The process for separating substances in a mixture by evaporating a liquid and recondensing its vapor

  • Two liquids having different boiling points can be separated in a similar way.

• Chemical Properties and Changes

  • Chemical Property: a characteristic of a substance that indicates whether it can undergo a certain chemical change.

  • The tendency of a substance to burn, or its flammability, is an example of a chemical property because burning produces new substances during a chemical change.

  • Reaction to light is a chemical property.

• Detecting Chemical Change

  • Chemical Change: A change of one substance to another.

  • Clues such as heat, cooling, or the formation of bubbles or solids in a liquid are helpful indicators that a reaction is taking place.

  • In some chemical changes, a rapid release of energy—detected as heat, light, and sound—is a clue that changes are occurring.

  • The only sure proof is that a new substance is produced.

  • Tarnish is a chemical reaction between silver metal and sulfur compounds in the air which results in silver sulfide.

• Weathering - Chemical or Physical Change?

  • The forces of nature continuously shape Earth’s surface.

  • Weathering can involve physical or chemical change.

• Law of Conservation of Mass: the mass of all substances that are present before a chemical change equals the mass of all the substances that remain after the change.

  • Smoke, heat, and light are given off and the changes in the appearance of a log confirm that a chemical change took place.

  • Not only is no mass lost during burning, mass is not gained or lost during any chemical change.