elements, compounds & mixtures

• Pure substance


  Particles that are all the same. Pure substances are either elements or compounds.
• Impure substance


  Particles of more than one kind. Mixtures are impure substances.
• Pure substances


  • Fixed composition
  • Distinct properties
  • Cannot be separated into simpler substances by physical methods
  • Can only be changed in identity and properties by chemical methods
  • Properties do not vary one sample to another sample
• Element


  Pure substance that cannot be separated into simpler substance by physical or chemical means. Made up of one type of atom.
• Elements


  • Oxygen
  • Nitrogen
  • Carbon
• Compound


  Pure substance composed of two or more different elements joined by chemical bonds. Made of elements in a specific ratio that is always the same. Has a chemical formula. Can only be separated by chemical means, not physically.
• Compounds


  • H2O
  • CO2
  • NaCl
• Mixture


  Combination of two or more pure substances that are not chemically combined. Impure substances. Substances held together by physical forces, not chemical. No chemical change takes place. Each item retains its properties in the mixture. They can be separated physically.
• Homogeneous mixture (Solution)


  Uniform distribution
• Homogeneous mixtures


  • Tea
  • Perfume
  • Air
• Heterogeneous mixture


  Non-uniform distribution. Parts are often visible.
• Heterogeneous mixtures


  • Salad
  • Beach sand
  • Oil and vinegar dressing
• Mixtures are often referred to as homogeneous or heterogeneous
• Two elements mixed together

  Can form a compound or a mixture
• A mixture can contain both elements and compounds
• An element contains just one type of atom
• A compound contains two or more different atoms joined together
• A mixture contains two or more different substances that are only physically joined together, not chemically