Compounds and mixtures

• Molecule

  A group of two or more atoms that are held together by chemical bonds
• Molecules

  • Oxygen
  • Water
  • Nitrogen
  • Chlorine
  • Carbon dioxide
• Helium existing as a single atom would not count as a molecule</b>
• Compound

  A substance that contains two or more different elements, with the atoms held together by chemical bonds
• Compounds

  • Water
  • Carbon dioxide
• Oxygen, chlorine, and nitrogen are not compounds because they only contain one type of element
• Compounds

  • The elements involved are always found in the same proportions
• Chemical formula

  Uses chemical symbols and numbers to represent the composition of a molecule or compound
• Chemical formulas

  • H2O
  • CO2
  • H2SO4
  • Ca(OH)2
• Some compounds can contain millions or billions of atoms, such as sodium chloride
• Mixture

  Two or more substances that are not chemically combined, but physically mixed together
• Mixtures can be separated using physical methods like filtration, crystallization, or distillation