Chemical formulae of compounds

• What do chemists use to represent elements and compounds?

  Symbols and formulae
• What do word equations and balanced chemical equations represent?

  The changes that happen in chemical reactions
• What is a compound?

  • A substance formed by the chemical union of two or more elements
  • Contains elements that are chemically combined
  • Elements are present in fixed proportions
• How is carbon dioxide represented in terms of its composition?

  It has 12 g of carbon for every 32 g of oxygen
• What does a chemical formula indicate?

  The chemical composition of a substance
• What does the formula of a compound show?

  The symbols for each element and the number of atoms of each element
• What is the formula for magnesium oxide?

  MgO
• What does the subscript in a chemical formula indicate?

  If there is more than one atom of an element
• What are some examples of compounds and their formulas?

  • Sodium chloride: NaCl
  • Potassium bromide: KBr
  • Magnesium iodide: MgI₂
  • Carbon dioxide: CO₂
  • Carbon monoxide: CO
  • Sulfur trioxide: SO₃
  • Water: H₂O
  • Ammonia: NH₃
  • Methane: CH₄
• How can compounds be formed from their elements?

  Through chemical reactions
• What is a chemical reaction?

  A change in which atoms are rearranged to form new substances
• What often occurs during a chemical reaction?

  Energy changes
• What is required to split a compound into its elements?

  A chemical reaction
• What is a key fact about compounds made up of non-metal elements?

  • The second word of the compound's name starts with mon-, di-, or tri-
  • Indicates the number of atoms of that element for every one atom of the first element
  • Example: In carbon dioxide, there are two oxygen atoms for every carbon atom