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