Ion - Download as DOC

							      CHAPTER 5 NOTES: CHEMICAL FORMULAS

I. Vocabulary and General Information
A. Atom – neutral particle (#positive protons = # negative
electrons)   Symbol: Na       Name: sodium atom

B. Octet Rule – atoms gain, lose or share electrons to fill
valence shell (stable with 8. Exception: H, He with 2)

C. Ion – charged particle due to transfer of electrons.
   a. Cation – loses electrons  positive ion (metals)
             +
      Ex: Na     Name: sodium ion
   b. Anion – gains electrons  negative ion (nonmetals)
            2-
      Ex: O      Name: oxide

D. Isoelectric – ions that have the same number of
electrons as a noble gas.
     Ex: Bromine atom (Br )



         Bromine ion (Br-)

E. Representative elements – Groups 1, 2, 13-18

F. Oxidation number or ionic charge – the number of
electrons that must be gained, lost or shared by an atom in
forming a compound.
GROUP #        VALENCE    # ELECT. IONIC
              ELECTRONS LOST/GAINED CHARGE
     1
     2
    13
    14
    15
    16
    17
    18

*All elements in these groups have the same ionic charge.

G. Polyatomic ion – a tightly bound group of atoms that
behave as one unit and carry a single charge.
     Ex. Formula: PO43-
          Name:      Phosphate ion
 ***See chart
II. Naming and Writing Formulas:
A. Ionic Compounds - composed of positive and negative

   ions (metal + nonmetal)
     1. Binary ionic compounds – cation + anion (2 elements)

  Examples: KCl, MgO
        a. Writing formula from name: write symbol and ion

           charge of each ion; cation always written first.
        b. Use criss-cross method

        c. Use subscripts to balance charges

        d. Examples: sodium oxide




                      Calcium sulfide



       e.   Naming from formula – Name of cation + anion + “ide”
            Ex: KBr                SrCl2              Li2O



    2. Ternary ionic compounds – contains 1 or more
       polyatomic ions
         Example: NaNO3
      a. Writing formula from name – write symbol and ion
         charge of each ion; cation always written first.
      a. Use criss-cross method

      b. Use parenthesis around polyatomic ions (if needed)

      c. Use subscripts to balance charges
  d.   Examples:   potassium nitrate



       Calcium sulfate        magnesium hydroxide



  e.Naming from formula:
  Name of cation (or poly. Ion) + name of anion (or
  poly. Ion).
  Examples: NaOH             NH4Cl          NH4NO3



3. Transition elements – groups 3-12
  a. Most have more than 1 ionic charge

     ● Can lose valence electrons (s, p) and also some

        d subshell electrons
               2+
     ● Ex. Fe             Fe3+
  b. A few transition elements have only 1 charge.

     - Ex: Ag+       Cd2+ Zn2+
  c. Writing formula from name –

     transition element + anion (or poly. Ion)
  d. Ex: iron II sulfate           mercury II oxide



  e.   Writing name from formula – 2 methods:
       -Stock System – metal’s name with Roman
       numeral to indicate charge
        Ex. Fe(OH)2            HgO
           -Classical System – use metal’s Latin name and
           either –ous or –ic ending.
           Lower charge: -ous ending Ex. Fe2+ = ferrous
           Higher charge: - ic ending Ex. Fe3+ = ferric

          Ion            Stock Name        Classical Name
          Cu1+
          Cu2+
          Hg1+
          Hg2+
          Fe2+
          Fe3+
          Sn2+
          Sn4+
                   YOU MUST KNOW THESE!!
B.    Covalent Bonding
1.   Binary molecular compounds – 2 nonmetallic elements
2.   Diatomic molecules – 2 atoms of the same element
     covalently bonded
     a. Occur naturally as pairs and have no charge

     b. Br2, I2, N2, Cl2, H2, O2, F2 (BrINClHOF)
3.   Naming: Prefixes show how many atoms of each element
     are present in a molecule.
     a. Prefixes (Know these!):
        1 – mono        4 – tetra         7 – septa (hepta)
        2 – di          5 – penta         8 – octa
        3 – tri         6 – hexa          9 – nona
                                          10 – deca
     b. Name: (prefix + 1st element) + (prefix + 2nd element + ide)
                                      st
     c. Prefix “mono” – not used on 1    element when naming
        compound.
     d. Drop vowel at end of prefix IF element’s name begins

        with vowel (Exceptions: di- and tri-)
     e. Examples:     CO        carbon monoxide
                      SO9       sulfur nonoxide
                      CO2       carbon dioxide



C.    Acidic Compounds
1.   Chemical formula always begins with hydrogen (H).
2.   Acid name depends on the anion:
     a. If anion ends in –ide, change to hydro + -ic.

        Ex. HCl = chloride      hydrochloric acid
     b. If anion ends in –ate, change to –ic.

        Ex. HClO3 = chlorate      chloric acid
     c. If anion ends in –ite, change to -ous.

        Ex. HClO2 = chlorite       chlorous acid
3.   Chemical formula:
     a. Acids are treated like ionic compounds

     b. H will always be the positive ion

     c. Determine the anion from the name (see #2 above)

     d. Determine the ion charges and criss cross

     e. Ex:   Carbonic acid
             “-ic” means “ate”
             which means “carbonate”
             H+     CO32-
             Becomes: H2CO3