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1 why atoms combine

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1 why atoms combine

  1. 1. Why Atoms Combine
  2. 2. <ul><li>Compounds- have properties unlike those of their elements </li></ul><ul><li>Ex: Na + Cl = NaCl (salt) </li></ul><ul><li>Sodium= metal that reacts violently with water. </li></ul><ul><li>Chlorine= green poisonous gas </li></ul>
  3. 3. <ul><li>Formulas = chemical shorthand for a compound. It tells what elements it contains and the ratio of the atoms of each element. </li></ul><ul><li>NaCl is formula for (sodium chloride) salt. </li></ul>
  4. 4. <ul><li>Subscript = number written below in a formula. It tells you the number of atoms of each element that makes up the formula. </li></ul><ul><li>If a symbol has no subscript, there are only 1 atom of that element. </li></ul>
  5. 5. <ul><li>Ex: H 2 O Subscript 2 </li></ul><ul><li>Hydrogen = 2 atoms </li></ul><ul><li>Oxygen = 1 atom </li></ul><ul><li>Ex: Fe 2 O 3 Iron III Oxide </li></ul><ul><li>Iron = 2 atoms </li></ul><ul><li>Oxygen = 3 atoms </li></ul>
  6. 6. <ul><li>Superscript - the number written above in a formula. </li></ul><ul><li>The number is either a + or – number. </li></ul><ul><li>It tells the charge of the elements. </li></ul>
  7. 7. <ul><li>Ex: Magnesium ( Mg +2 ) </li></ul><ul><li>Oxygen ( O -2 ) </li></ul><ul><li>Mg +2 O -2 = Magnesium Oxide </li></ul><ul><li>Sodium (Na +1 ) </li></ul><ul><li>Chlorine (Cl -1 ) </li></ul><ul><li>Na +1 Cl -1 = Sodium Chloride </li></ul>
  8. 8. Chemically stable atoms <ul><li>A stable atom has its outer energy level filled with 8 valence e-. </li></ul><ul><li>All noble gases are stable. </li></ul><ul><li>Helium is stable with only 2 atoms (1 st energy level = 2 e-). </li></ul>
  9. 9. <ul><li>The rest of the elements have 1-7 electrons in its outer energy level. These atoms lose, gain or share e- </li></ul><ul><li>All the atoms want to be stable (have 8 e-). </li></ul>
  10. 10. <ul><li>Chemical Bond- a force that holds together atoms in a compound. </li></ul>

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