Chapter 15: Classification of Matter 

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. \n \n

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