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
    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.