Chapter 18: Classification of Matter 

Section 1: Composition of Matter

  • Pure Substances
    • Every material has its own properties. The properties of materials can be used to classify them into general categories.
    • Substance: type of matter with a fixed composition
    • A substance can be either an element or a compound.
    • Element: If all the atoms in a substance have the same identity
    • About 90 elements are found on Earth.
    • All the atoms of an element are alike.
    • Compound: a pure substance in which the atoms of two or more elements are combined in a fixed proportion.
    • Chlorine gas and sodium metal combine dramatically in the ratio of one to one to form sodium chloride.
    • A particle consisting of two or more atoms that are bonded together is called a molecule.
    • A molecule is a basic unit of a molecular compound.
  • Mixtures
    • A mixture is a material made up of two or more substances that can be easily separated by physical means.
    • The number of mixtures that can be created by combining substances is unlimited
    • Mixtures do not always contain the same proportions of the substances that make them up.
    • Heterogenous Mixture: A mixture in which different materials can be distinguished easily
    • Heterogeneous mixtures can be hard to detect.
    • Homogeneous Mixture: contains two or more gaseous, liquid, or solid substances blended evenly throughout.
    • 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.
    • Solutions remain constantly and uniformly mixed.
    • All matter can be divided into substances and mixtures.
    • Colloid: a type of mixture with particles that are larger than those in solutions but not heavy enough to settle out.
    • One way to distinguish a colloid from a solution is by its appearance.
    • Fog is a colloid composed of water droplets suspended \n in air.
    • Tyndall Effect: The scattering of light by colloidal particles
    • Suspension: a heterogeneous mixture containing a liquid in which visible particles settle.
    • River deltas are large scale examples of how

      a suspension settles.

Section 2: Properties of Matter

  • Physical Properties

    • The abilities to stretch and bend are physical properties.
    • Physical Property: Any characteristic of a material that you can observe without changing the identity of the substances that make up the material
    • Appearance is the most obvious physical property.
    • 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.
    • The best way to separate substances depends on their physical properties.

  • Physical Changes

    • When a substance freezes, boils, evaporates, or condenses, it undergoes physical changes.
    • Physical Change: A change in size, shape, or state of matter
    • Iron is a substance that can change states if it absorbs or releases enough energy; at high temperatures, it melts.
    • Heating iron raises its energy level and changes its color. These energy changes are physical changes because the substance is still iron.
    • One separation method, which uses the property of boiling point, is distillation.
    • Distillation: The process used for separating substances in a mixture by evaporating a liquid and recondensing its vapor
    • Distillation can easily separate liquids from solids dissolved in them. The liquid is heated until it vaporizes and moves up the column. Then, as it touches the water-cooled surface of the condenser, it becomes liquid again.

  • Chemical Properties and Changes

    • The tendency of a substance to burn, or its flammability, is an example of a chemical property.
    • Chemical Property: a characteristic of a substance that indicates whether it can undergo a certain chemical change.
    • Many medicines are stored in dark bottles because they contain compounds that can change chemically if they are exposed to light.

  • Detecting Chemical Changes

    • Chemical Change: A change of one substance to another
    • In some chemical changes, a rapid release of energy—detected as change of heat, light, and/or sound production—is a clue that changes are occurring.
    • Burning and rusting are chemical changes because new substances form.
    • The solid forming from two liquids is another sign that a chemical reaction has taken place.
    • You might separate substances using a chemical change when cleaning tarnished silver.

  • Weathering - Chemical or Physical Change

    • The forces of nature continuously shape Earth’s surface.
    • Weathering can involve physical or chemical change.
    • Flowing water shaped and smoothed these rocks in a physical process.
    • Both chemical and physical changes shaped the famous White Cliffs of Dover lining the English Channel.

  • The Conservation of Mass

    • Wood is combustible, or burnable.
    • Not only is no mass lost during burning, mass is not gained or lost during any 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. \n