OXIDATION NUMBER
• Oxidation number = the charge an atom
would acquire if all its bonds were treated
as ionic bonds.
• To determine how many atoms combine
with one another in a compound we must
determine each element’s OXIDATION
NUMBER.
Predicting Ionic Charges
Group 2:
2: Loses 2 electrons to form
2+ ions
Predicting Ionic Charges
Group 1:
1: Lose 1 electron to form 1+ ions
H+
Li+
Na+
K+
Predicting Ionic Charges
B3+
Group 13:
13: Loses 3
electrons to form
3+ ions
Al3+
Ga3+
Be2+
2
M 2+
Mg
2+
Ca
Sr2+
Ba2+
Predicting Ionic Charges
Group 14:
14:
Lose of 4
electrons or gain
of 4 electrons?
Neither! Group 14
elements rarely form
ions.
Predicting Ionic Charges
N3- Nitride
P3- Phosphide
As3- Arsenide
Group 15:
15: Gains 3
electrons to form
3- ions
1
Predicting Ionic Charges
O2- Oxide
S2- Sulfide
Se2- Selenide
Group 16:
16:
Gains 2
electrons to form
2- ions
Predicting Ionic Charges
Group 18:
18:
Stable Noble gases
do not form ions!
Predicting Ionic Charges
Groups 3 - 11
11:: Some metals
have only one possible oxidation state.
Silver = Ag+
Zinc = Zn2+
Predicting Ionic Charges
F1- Fluoride
Br1- Bromide
Cl1-Chloride
I1-
Iodide
Group 17:
17:
Gains 1
electron to form
1- ions
Predicting Ionic Charges
Groups 3 - 11
11:: Many transition elements
have multiple oxidation states.
Iron(II) = Fe2+
Iron(III) = Fe3+
Rules for assigning Oxidation
Numbers
1. The atoms in a pure element have an oxidation number of zero.
2. Alkali metals always have an oxidation number of +1; alkaline
earth metals always have an oxidation number of +2.
3. Fluorine always has an oxidation number of -1.
4. Oxygen
yg has an oxidation number of -2 in almost all compounds.
p
Exceptions are in compounds with a halogen, when it has an
oxidation number of +2, and in peroxides (H2O2), when it has
an oxidation number of -1.
5. Hydrogen has an oxidation number of +1 in almost all
compounds except when combined with a metal when it has an
oxidation number of -1.
6. The sum of all the oxidation numbers in a neutral compound is
zero.
7. The sum of all the oxidation numbers in a polyatomic ion is
equal to the charge of the ion.
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ASSIGNING OXIDATION
NUMBERS
• A compound has a total charge of ZERO so set
your equation equal to ZERO.
• Assign the variable X to your unknown oxidation
number.
• Given a compound, find the oxidation number of
every element you know for certain. Then solve
for others using algebra.
• KMnO4
Do you notice a pattern with the elements in these compounds?
H2+1 O1‐2
Mg1+2F2‐1
Al2+3S3‐2
Cu3+1P1‐3
Ca1+2Cl2‐1
Fe2+3O3‐2
• CaCO3
CRISS-CROSS METHOD
to determine the chemical formula
1. Write the symbols for the elements side by side.
2. Write the oxidation states of each element to the
top right of the symbol. When the nonmetal is
combines with a metal, the oxidation state will
always
l
b
be th
the first
fi t number
b (the
(th negative
ti one)) iin th
the
list of oxidation states.
3. Criss cross the charges DOWN and use the
absolute values (-2 becomes 2).
4. Check to make sure the subscripts are the lowest
ratio.
Practice Criss-Cross Method
1. Na and S
2. K and P
3. Al and S
What about Polyatomic Ions?
4. Mg and Br
• Write down the only cations on Table E:
(positively charges ions)
5. Al and O
• Write down the only polyatomic ions that
end in –ide.
3
Polyatomic Ions Chart (Table E)
Polyatomic Ions
• If you see a group of atoms together with a charge it is a polyatomic ion from Table E.
• Put the polyatomic ion within Parenthesis.
• Find the charge of the polyatomic ion.
• Use the criss‐cross method to determine subscripts.
Na +1 CO3‐2
How many atoms are present in the compound?
Find the charge of the polyatomic ion using Table E
Put parenthesis around the polyatomic ion.
1. PO4
7. HSO4
2. CO3
8. ClO4
3. SO3
9. CN
4. NH4
10. OH
5. ClO
11. S2O3
6. ClO2
12. SCN
Rules for writing the formula of
the compound composed of ions
1. Place all Polyatomic Ions in Parenthesis
(Table E)
2. Determine all oxidation numbers of
elements and polyatomic ions
3. Use Criss-Cross Method
4. Reduce to Empirical Form
NH4 +1 S‐2
How many atoms are present in the compound?
Practice
4. Al SO4
1. NH4 S
5. Fe CO3
2. Na NO3
3. Cu Br
6. Pb PO4
4
7. Ag ClO
10. Cu OH
8. Ca F
11. Ni I
12. Zn SO4
9. NH4 SO3
13. Pb ClO2
14. H I
15. Fe HSO4
16. Cu CO3
17. NH4 O
18. Ag S
19. Al ClO4
Of the following metals listed below,
check off all the elements that have
more than one oxidation state:
NAMING IONIC COMPOUNDS
• An Ionic compound can quickly be
determined if a METAL is bonded to a
NONMETAL.
• Naming Ionic compounds with metals that
have only ONE oxidation state is fairly
simple.
a. Mn___
b. Zn ___ c. K ____
d. Pb___
e. Mg
Mg___
f. Au ___ g. Ag ___
h. Ga__
Ga
i.
j. Li ____ k. U ____
l. Cr ___
Sn __
5
Naming Ionic Compounds that
contain metals with 1 oxidation state
• Binary Ionic Compounds = ionic
compounds with only 2 different
elements.
• Name the metal and end the nonmetal in
–ide.
• For example: CaBr2 = Calcium Bromide
Name the following Binary
compounds:
1. MgO=
Magnesium Oxide
Naming Binary Ionic Compounds
• Naming salts is very easy, because they are binary ionic
compounds (made up of two elements).
– The cation is named by using the name of the element.
– The anion named by combining the name of the element
with an –ide ending.
• The name of compound is made up of both the cation and
anion name
– Ex: NaCl = sodium chloride
– Ex: ZnS = zinc sulfide
– Ex: K2O = potassium oxide
– Ex: Mg3N2 = magnesium nitride
– Ex: Al2S3 = aluminum sulfide
4. Ag3N = _______________________
5. Al2O3 = ______________________
2. CaCl2 = _______________________
6. LiI = _________________________
3. AlBr3 = _______________________
7. BaF2 = _______________________
8. Zn2C = _______________________
9. Ba3N2 = ______________________
10.CdO = _______________________
11. Ga2S3 = _______________________
What about Polyatomic ions?
(Table E)
• These are ions consisting of more than
one atom. The names of polyatomic ions
end in –ate or –ite, except for two
(ammonium and cyanide)
12. K3N = ________________________
13. SrO = ________________________
6
Polyatomic ion chart (Table E)
Ternary Ionic Compounds
• Ionic Compounds with 3 different elements.
• They usually contain Polyatomic Ions (Table E)
Name the following Polyatomic Ions:
• a.
a NO3- nitrate
d SO42- ___________
d.
• b. ClO2- _________ e. SO32- __________
• c. CO32- _________ f. SCN- ____________
Naming Ternary Compounds
Naming Ternary Compounds
• Name the metal and then name the
polyatomic ion (if it has a negative
oxidation number).
• Name the polyatomic ion (if it has a
positive oxidation number) and then
name the nonmetal.
• For example: KNO3 = Potassium nitrate
• For example: NH4Cl = ammonium chloride
METAL
Naming Ternary Compounds
• If there are two polyatomic ions, name the
positive polyatomic ion first and then
name the negative polyatomic ion.
• For example: NH4NO3 = ammonium nitrate
POSITIVE
POLYATOMIC ION
POLYATOMIC
ION
POLYATOMIC
ION
NEGATIVE
POLYATOMIC
ION
• DO NOT CHANGE THE ENDINGS OF
POLYATOMIC IONS!
NONMETAL
Name the following Ternary compounds:
1. NaC2H3O2
2. AgHCO3
Sodium acetate
Silver hydrogen carbonate
3. LiNO2 _________________________
4. Ga2(S2O3)3 ____________________
5. Ca3(PO4)2 _____________________
7
6. ZnSO3 __________________________
Naming Ionic Compounds with Metals with
Multiple oxidation states (multiple charges):
Using the STOCK SYSTEM
7. KClO3 ___________________________
8. Al(OH)3 _________________________
9. RbSCN __________________________
10. SrCO3 _________________________
1. Determine the oxidation state of the metal
in the compound.
2. Name the metal, put the oxidation state in
ROMAN NUMERALS in parenthesis
1. I = 1, II = 2, III = 3, IV = 4, V = 5
3. End the nonmetal in –ide.
Review: Find the Formula
Pb+4 O-2
Criss-Cross
(bring down)
Pb2 O4
Find Empirical
formula
Pb O2
Empirical
Formula
Fe1O1
Cu+2 (SO4) -2
Sn+2(CO3) -2
Work Backwards: Start with the Empirical Formula to determine the Oxidation state of a Metal with Multiple Oxidation States
Empirical
Formula
Work Backwards: Start with the Empirical Formula to determine the Oxidation state of a Metal with Multiple Oxidation States
Write in the oxidation
number for the nonmetal
or polyatomic ion you are
sure of and criss-cross.
Sn1(SO3)1
Sn ((SO3)
Mn1(SO4)2
Mn (SO4)
Non-reduced form with
Oxidation States
Write in the oxidation
number for the nonmetal
or polyatomic ion you are
sure of and criss-cross.
Fe+2 O-22
Fe1(SO4)1
Fe (SO4)
Cu1(SO4)1
Cu (SO4)
Non-reduced form with
Oxidation States
Fe2O2 reduce
to FeO
Name the following compound using the Stock System:
1. Fe O Æ Fe+2 O-2 ÆFe2O2 Æ Iron (II) Oxide
2 Fe Cl2 ___________________________
2.
3. Cu SO4 __________________________
4. Pb Cl2 ___________________________
Cr1(PO4)2
Cr (PO4)
8
5. Pb O2 ___________________________
6. Cu3(PO4)2 ________________________
7. Cu2 S ___________________________
8. Fe2(CrO4)3 ______________________
19. Sn CO3 _________________________
10. Sn F4 ___________________________
Name each of the following
compounds, use Roman Numerals
only when necessary.
Put a check next to every compound that begins
with a metal with more than 1 oxidation state.
Put parenthesis around all the polyatomic ions.
ions
1. NH4 Cl _________________________
2. Pb SO4 _________________________
3. Co Cl3 __________________________
9. Cu S __________________________
4. Ba (NO3)2 ______________________
5. Co2 (SO3)3 _____________________
6. KH ____________________________
7. NH4 F _________________________
8. K2Cr2O7 _______________________
10. Cu ClO2 ______________________
11. Ag NO3 _______________________
12 F
12.
Fe Cl3 ________________________
13. Cr F2 _________________________
14. Na Cl _________________________
15. Fe PO4 ______________________
16. Li F _________________________
17. Fe F3 _______________________
18. Al (OH)3 _____________________
19. Mg I2 ________________________
20. Fe Cl3 _______________________
9