Writing formulas for Ionic Compounds. Review Ionic compounds are composed of cations (metals) and...
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Transcript of Writing formulas for Ionic Compounds. Review Ionic compounds are composed of cations (metals) and...
Writing formulas for Ionic Compounds
Review• Ionic compounds are composed of
cations (metals) and anions (nonmetals).
• Although they are composed of ions, ionic compounds are electrically neutral. The positive charge equals the negative.
• The positive charge and the negative charge attract one another. This is how the bond is formed.
Writing Binary Ionic Formulas
• The cation (Metal) with the correct oxidation number is written first
• The anion (nonmetal) with the correct oxidation number is written second
Binary Ionic Formulas
• Criss– cross the charges from superscripts to subscripts using only their absolute value
For Example
A+2 B-3
A3 B2
• Check to make sure the subscripts are in the lowest possible ratio to one another
For Example:
A4B6
A2B3
Example
Write the correct ionic formula for Barium and Chlorine.
Step 1: Write the cation (with correct oxidation number) first
And the anion (with the correct oxidation number second)
Barium and Chlorine
Ba+2Cl-1
Step 2: Criss-cross the superscripts to subscripts using only the absolute value
Ba+2Cl-1
BaCl2
Why is there no subscript for Ba?
Step 3: Make sure all subscripts are in the lowest possible ratio.
BaCl2
If there are in the lowest possible ratio you are done!!
Writing Formulas for Ternary Ionic Compounds
(3+ Elements)• Formulas of Ionic compounds Containing
Polyatomic Ions- it is imperative that you know the correct charges on these ions!!!!! When using multiple polyatomics, you must “keep it together” by putting it in parenthesis.
• Example: Ca3(PO4)2 - calcium phosphate
• The charge must still equal zero!
Write the correct formula for the following binary ionic compounds:
• Potassium and Iodine
• Calcium and Fluorine
• Aluminum and Sulfur• Iron(III) and Oxygen (watch out for the transition metal)
Writing Formulas for Ternary Ionic Compounds
(3+ Elements)
• Write the formula for:
sodium phosphate:
ammonium sulfide: