Transcript part 1.writing chemical formulas for ionic compoundsv2

Writing and Naming Chemical
Formulas for Ionic
Compounds: Part 1
Science 10
Chemical Formulas
A chemical formula provides you with TWO
important pieces of information:
1. The elements that make up the
compound.
2. The number of atoms of each
element that are present in the
compound.
Number of Atoms
• In an ionic compound, the formula
represents the ratio of each atom
present in a compound.
– Example: In the compound Li2O, there
are 2 lithium atoms for every 1 oxygen
atom.
How many atoms are shown?
• Example 1:LiNO3
– 5 atoms
• Example 2:Mg(OH)2
- 5 atoms
• Example 3: (NH4)3PO4
• - 20 atoms
Valence Numbers
• We have already used Lewis structures to
determine the chemical formulas of
compounds, but this can get to be quite
tedious (especially with large compounds).
• We will now use the shorthand method of
determining chemical formulas ~ using
combining capacities (AKA: valence
numbers).
Valence Numbers (Continued)
• A positive valence number indicates the loss
of electrons.
• A negative valence number indicates the
gaining of electrons.
• The number next to the + or – indicates
HOW MANY electrons are lost or gained to
achieve a stable octet, and therefore form
a compound.
Writing Chemical Formulas for
Simple Ionic Compounds
1. Write the atom’s symbols with their
combining capacities (as superscripts).
2. Crisscross the combining capacities, and
write them (WITHOUT the + or -) as
subscripts.
3. Write the final chemical formula.
- If there are any 1’s, remove them.
- If the subscripts are multiples of each
other, reduce them.
Examples:
1. calcium fluoride
CaF2
2. zinc oxide
ZnO
3. Potassium sulphide
K2S
4. barium phosphide
Ba3P
Naming Simple Ionic Compounds
1. Write the name of the metal first.
2. Followed by the name of the nonmetal).
3. Remove the ending of the non-metal
and add “ide”.
Examples:
1. KCl
Potassium chloride
2. CaO
Calcium Oxide
Multivalent Transition Metals
• Are multivalent (have more than one
combining capacity or valence)
• Roman numerals are used to indicate
which combining capacity is to be used
Writing Chemical Formulas for
Compounds Containing Transition
Metals
1. Write the atom’s symbols with their combining
capacities (as superscripts).
- Please note that the combining capacity that
you use for the transition metal is indicated by
the Roman numeral in the name.
2. Crisscross the combining capacities, and write
them (WITHOUT the + or -) as subscripts.
3. Write the final chemical formula.
- If there are any 1’s, remove them.
- If the subscripts are multiples of each other,
reduce them.
Examples:
1. iron (III) oxide
Fe2O3
2. iron (II) oxide
FeO
3. Lead (IV) sulphide
PbS2
4. mercury (II) oxide
HgO
Naming Multivalent Compounds
Step 1: Write the names of the metal and
non-metal, leaving a space after the metal
for a roman numeral
Step 2: Reverse ‘criss cross’, this will give
you the ion charge of the metal. The nonmetal charge is always constant (look at
periodic table)
Step 3: Write formula including roman
numeral for metal. **NOTE watch for
reducing**
Example: FeCl3
• Step 1: write names of elements
Iron Chloride
• Step 2: - reverse criss cross
Iron – Ion charge of 3+ (from formula),
Chlorine – ion charge of 1- (always and
forever)
• Step 3: Iron(III)Chloride
Examples:
1. Fe2O3
- Iron(III)Oxide
2. MnS
- Manganese(II)Sulphide
3. MnS2(Watch out for LOWEST TERMS!)
- Manganese(IV)Sulphide
Try the Magic Formula!!!!
1. Fe2O3
Answer - Iron (III) Oxide
2. MnS – watch for reducing – -hint S is always 2Answer – Manganese (II) Sulphide
3. MnS2
Answer – Manganese (IV) Sulphide – again check for
reducing – Sulphide is 2-, Manganese was
reduced from 4+
Homework
• Do practice problems pages 188,190,191
– copy question on a separate sheet of
paper – check answers in back of book
• Worksheets
– One common ion charge
– Multiple ion charges
– Mixing it up