SCH 3U/4C - Nomeclature - Prefix Naming System

Another method of naming compounds in which the first element (usually P, S, C, N, Si) may have more than one valence is called the prefix system.  This method is used only with compounds containing two non-metals. 

Prefixes:                1        mono-

                              2        di-

                              3        tri-

                              4        tetra-

                              5        penta-

                              6        hexa-

                              7        hepta-

                              8        octa-

                              9        nona-

                             10       deca-

Rules for Writing a Name from a Formula

1.     Write down the name as you did for binary compounds.

2.    Include a prefix with the first element name that indicates how many of the first atom are present.  However, if there is only one atom in the first position, do not use the mono- prefix.

3.    Include a prefix with the second element name that indicates how many of the second atom are present.

ex. (a)  CO         carbon monoxide

      (b)  N₂O       dinitrogen monoxide

      (c)  SCl₃       sulfur trichloride

              

Rules for Writing a Formula from a Name

1.  Just write what the name tells you.

ex.(a)  dinitrogen tetroxide            N₂O₄

     (b)  sulfur hexafluoride             SF₆

     (c)  diphosphorus pentoxide     P₂O₅

Can't have too much prefix in your life?  Check out this video.

Homework

Give the correct formula for the following.

1.     sulfur trioxide

2.    carbon monoxide

3.    phosphorus triiodide

4.    silicon tetrafluoride

5.    sulfur dioxide

6.    diphosphorus pentoxide

7.    carbon tetraiodide

8.    diphosphorus pentasulfide

9.    sulfur hexabromide

10.  silicon disulfide

Give the correct name for the following.

1.     CO₂

2.    CO

3.    CS₂

4.    SO₂

5.    P₂O₃

6.    CCl₄

7.    PCl₃

8.    SiO₂

9.    P₂O₅

10.  SCl₆

 

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