Atomic structure and the periodic table

• How many elements are there?

  118
• Chemical reactions always involve the formation of one or more new __________, and often involve a detectable ______/______.

  Chemical reactions always involve the formation of one or more new SUBSTANCES, and often involve a detectable ENERGY CHANGE.
• Compounds are..?


  Two or more elements chemically combined in fixed proportions
• How can compounds be separated into elements?


  Chemical reactions
• The elements in group 1 are..?


  Alkali metals
• The elements in group 7 are..?


  Halogens
• The elements in group 8 are..? Why are these unreactive?


  Noble gases have a full outer shell of electrons
• A mixture is..?


  two or more elements or compounds not chemically combined together.
• How are mixtures separated?


  Physical processes that do not involve chemical reactions and no new substances are made.