MK

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