Unit #1Unit #2Unit #3Unit #4Unit #5Unit #6Unit #7Unit #8Unit #9Unit #10
spacerUNIT # 5  
spacerspacerIntroduction
spacerspacerObjectives
spacerspacerReading


spacer5.1 Ionic
spacerBonding

spacerIonic Bonding in Sodium Chloride
spacerIonic Bonding in Magnesium Chloride
spacerProperties of Ionic Compounds
spacer5.2 Covalent
spacerBonding
spacer5.3 Polar Covalent
spacerBonding

spacer5.4 Bond
spacerDipoles

spacer5.5 Electroneg-
spacerativity

spacer5.6 Classification
spacerof Bond Type
spacer5.7 Polarity of
spacerMolecules
spacer5.8 Writing
spacerChemical
spacerFormulae
spacerWriting formulas containing simple ions
spacerWriting formulas containing  polyatomic ions
spacerUsing parentheses in formula writing
spacer5.9 Information in
spacera Chemical
spacerFormula
spacerNumber ratio of atoms
spacerNumber ratio of ions
spacer5.10 Oxidation
spacerNumbers
spacerAssignment of Oxidation Numbers


spacerspacerProblems
spacer1 | 2

Unit #5 COMPOUNDS

5.8 -
Chemical Formulas for Ionic compounds

5.8.3 - Using parentheses in formula writing

In section 5.8.2 when we wrote the chemical formula for strontium nitrate we needed to put in a bracket around the NO3- ions to represent that in strontium nitrate, there are two NO3- ions.

In general,
When writing the chemical formula of a compound that contains a polyatomic ion, in order to indicate more than one polyatomic ion in the formula, put parentheses around the polyatomic ion before writing the subscript.

This does not apply if the subscript is '1'. When the subscript is '1', there is no need for any parentheses as it is usually not written.

For example,
Chemical Name
Correct Chemical Formula
Incorrect Chemical Formula
ammonium sulfate

Ions: NH4+, SO42-
(NH4)2SO4

Not sure how to figure out this formula?
Click to review section 5.8.2.

(NH4)2(SO4)
There is an extra bracket around the 'SO4' unit.

(NH4)2(SO4)1
Subscript of '1' is usually not written.

aluminum sulfate

Ions: Al3+, SO42-
Al2(SO4)3

Not sure how to figure out this formula?
Click to review section 5.8.2.
(Al)2(SO4)3
There is an extra bracket around 'Al'.

calcium chloride

Ions: Ca2+, Cl-

CaCl2

Not sure how to figure out this formula?
Click to review section 5.8.1.
Ca(Cl)2
There is an extra bracket around 'Cl'.

Section 6.9
Writing Formulas ..p147



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