Pure Substances and Mixtures

Pure Substances

Compounds

  • When two or more atoms combine, they form a compound.
  • Water is a molecular compound, composed of hydrogen and oxygen.
  • Salt is an ionic compound composed of ions like sodium and chloride.
  • "Particles" can describe atoms, ions, molecules, or ionic solids.

Compounds (cont.)

  • Compounds are pure substances made up of molecules or ionic solids.
  • Examples:
    • Water (Molecular: Hydrogen & Oxygen)
    • Salt (Ionic Solid: Sodium & Chlorine)

Compounds vs. Mixtures

  • Mixtures are combinations of particles that are not bound together by chemical bonds.
  • The proportions of each type of particle in a mixture are not fixed.
  • The composition of a mixture can be changed by adding more or less of each different particle.

Mixtures

  • If two substances are mixed together but don't combine to form a substance with new properties, it is a mixture.
  • Example: Salt and sugar mixed together do not form a new substance. They can be separated by physical processes.
  • Another example: A mixture of sand and water can be separated by pouring off the water or using a filter.

Pure Substances and Particles

  • A pure substance is composed of only one type of particle.
  • These particles can be atoms, molecules, or ionic solids.
  • Particles can include one type of atom or be composed of different atoms or ions.
  • A pure substance can be a compound and therefore contain different types of atoms that are chemically combined in fixed proportions.

Pure Substances Examples

  • Examples of pure substances include materials made of a single type of:
    • atom
    • molecule
    • ionic solid
  • Molecules and ionic solids may include different types of atoms.
  • A pure substance may be made of different atoms or ions, as long as they are bound together as molecules or as an ionic solid.
  • Mixtures of different particles are not pure substances.

Elements

  • Elements are pure substances made from only one type of atom.
  • Examples:
    • Gold
    • Silver
    • Carbon
    • Neon (Ne, Neon Gas)

Elements (cont.)

  • Gold atoms viewed with a powerful microscope, showing a pure gold nugget.