Science 8: Chapter 3 Naming polyatomic ions (notes)
Polyatomic ions Prefix “poly” means many.
A ____________________________ ion is an ion _________________________of more than one type of atom joined by
________________________ bonds.
Polyatomic ions carry an _________________________ charge, they cannot exist on their own.
Example of polyatomic ions:
1.
2.
3.
4.
5.
hydroxide ion
OH⁻
ammonium ion
________________
________________________ NH₄⁺
carbonate ion
________________
________________________ NO₃⁻
Use of polyatomic ions (Read page 79 and 80 to fill the table)
Use
1.
2.
3.
4.
5.
Tests for alcohol on driver’s breath
Forms the delicate shell of an egg
Major component of bones and DNA
Forms fertilizers
Forms the enamel of teeth
Name of polyatomic ion
dichromate ion
Formula
Cr₂O₇²⁻
Use phosphate ion (PO₄³⁻), as an example to answer the following questions
1. What kind of chemical bond holds each oxygen atom to the phosphorous atom? __________________________
2. How many atoms does the phosphorous atom connect to? ___________________________________________
3. What is the general term for an ion such as phosphate, which is a molecule that has an overall electric charge?
_________________________________________________________________________________________
4. In phosphate ion where are the covalent bonds and where are the ionic bonds?
__________________________________________________________________________________________________________________
__________________________________________________________________________________________________________________
Science 8: Chapter 3 Naming polyatomic ions (notes)
Rules for writing FORMULAS of a compound with polyatomic ions
Steps
sodium
hydroxide
1. Identify each
ion and its
charge , using
periodic table
and the list of
polyatomic
ions
2. Determine
total charge
needed to
balance
positive and
negative
3. Note the ratio
of positive
ions to
negative ions
4. Use brackets
and subscripts
to write the
formula.
Omit brackets
if only one ion
is needed.
Na⁺
OH⁻
Na⁺ = 1+
OH⁻ =1-
1
Na⁺
for
1
OH⁻
NaOH
ammonium
iron(III)
potassium
hydroxide
hydroxide
dichromate
tin(II) nitrate
ammonium
sulfate
Science 8: Chapter 3 Naming polyatomic ions (notes)
Write the NAME of compounds with polyatomic ions
Steps
Cu(OH)₂
1. Identify the positive
copper(Cu)
ion(using periodic table
or polyatomic list)
2. Verify that it can form
Cu ⁺ Cu ⁺²
more than one kind of
ion by checking the
periodic table
3. Identify the negative
OH⁻
ion (using the list of
polyatomic ions)
4. Determine the ratio of
ions in the formula
Cu(OH)₂ means 1
Copper ion for every
2 OH⁻ ion
5. The positive and
negative charges must
balance out. Determine
what the charge needs
to be on the metal ion
to balance the negative
ion
Each of the three
copper ions must
have a +1 charge to
balance the 2 OH⁻
ions Therefore,
copper(I)
6. Write the name
compound in lower
case
copper(I) hydroxide
MgSO₄
Ba₃(PO₄)₂
NH₄NO₃
Mn(ClO₃)₃
Science 8: Chapter 3 Naming polyatomic ions (notes)