Rules for Writing Charges

RULES FOR WRITING CHARGES

1.  Look up the group or valence number (number of outer shell electrons) for the element on

the periodic table.

2.  If the group number is 1, 2, or 13 then the charge is +1, +2, or +3.

3.  If the group number is 15, 16, or 17 then the charge is –3, -2, or –1 respectively.

4.  If the group number is 14 then the charge can vary usually +/-2 or +/-4.**

Group number 1 2 13 14 15 16 17 18

Valance number 1 2 3 4 5 6 7 8

Charge +1 +2 +3 ** -3 -2 -1 0

RULES FOR WRITING FORMULAS

1.  Write the atomic symbols and the charges for each ion or polyatomic ion.

2.  If the charges add up to zero write the formula as is.

3.  If the charges do not add up to zero write the charge number as a subscript on the opposite

symbol (don’t write the charge sign).

4.  If the charge is 1, you don’t need to write it.

RULES FOR NAMING COMPOUNDS

Ionic Compounds

a. Name the metal or positive ion just like the neutral element

b. Drop the ending on the negative ion and add the suffix -ide

ie. SrCl2 strontium chloride

c. If the ending is -ite or -ate then the polyatomic ion contains oxygen

d. Some polyatomic ions also end in -ide

ie. OH-1 in NaOH sodium hydroxide

NAMING BINARY COMPOUNDS OF NONMETAL (Molecular) COMPOUNDS

a. Write the names of the elements in the same order that they appear in the formula. The more metallic

non metal element is named first.

b. Drop the last syllable in the name of the final element and add -ide

c. Add prefixes to the name of each element to indicate the number of atoms of that element in each

molecule of the compound

d. see list of prefixes on back of this page

Note: the mono- prefix is frequently omitted, particularly for the more metallic (first) element.

If no prefix is given, one atom of that element is understood.

POSITIVE IONS (Cations) Partial list

Aluminum Al3+ hydrogen, hydronium H+, H30+ potassium K+

Ammonium NH4 + iron(II) Fe2+ scandium Sc3+

Barium Ba 2+ iron(III) Fe3+ silver Ag+

Cadmium Cd 2+ lead(II) Pb2+ sodium Na+

Calcium Ca 2+ Lithium Li+ Strontium Sr2+

Chromium(II) Cr2+ Magnesium Mg2+ Tin(II) Sn2+

Chromium(III) Cr3+ Manganese(II) Mn2+ Tin(IV) Sn4+

Cobalt (III) Co3+ Mercury (I) Hg22+ Zinc Zn2+

Copper (I) Cu+ Mercury (II) Hg2+

Copper (II) Cu2+ Nickel Ni2+