Transcript Oxidation Numbers

Chapter 8 Notes, part I
Writing Ionic Formulas
Compounds
•Up until now, we have only looked at
single elements.
•There are only (to date) just over 100
elements, so how do we account for
there being so many different types
of stuff?
Compounds
•There are millions of different
compounds—two or more elements
that are combined chemically.
•The two types of compounds we will
discuss in this chapter are ionic
compounds and covalent compounds.
A compound is a pure substance
made up of two or more elements that
are chemically joined in definite
proportions.
2 oxygen atoms
Carbon dioxide is CO2 , while
carbon monoxide (the poison) is
CO .
Ex.
1 oxygen atom
Compounds do not look or act like the
elements that form them.
•Sodium is
a silvery
metal that
reacts
violently
with water
•Chlorine
is a
poisonous,
green gas.
•Does salt
share any
of those
properties?
Oxygen + Hydrogen -----> Water
Hydrogen is
explosive!
Is water
explosive?
Ionic Compounds
•Last chapter we discussed ions—
elements that have a charge due to
losing or gaining electrons.
•Ionic compounds are made of ions.
Ionic Compounds
•Metals tend to form ions by losing
electrons, giving them an overall positive
charge. These are called cations.
•Nonmetals tend to form ions by gaining
electrons, giving them an overall negative
charge. These are called anions.
Ionic Compounds
•An ionic compounds is formed from a
cation and an anion, which means
they are usually formed from a metal
and a nonmetal.
IONIC Compounds
Ionic compounds consist of two oppositely charged ions.
Li+1 F-1
Positive ion – metal
Negative ion - nonmetal
LiLi+10
3p+
4n0
9p+
10n0
0
F-1
Covalent compounds occur
between two nonmetals.
Both nonmetals share electrons
8p+
8n0
6p+
6n0
8p+
8n0
Carbon dioxide
Atoms are stable,
or resistant to
change if their
outer energy level
is completely
filled with electrons.
10p
10n
NEON
3p
4n
Atoms of all the
elements have
9p
10n
from one to seven
electrons in
their outer energy
level except the noble gases.
When atoms lose or gain
Electrons they become
ions.
Single or Monoatomic ions
Ionic Compounds
•Anions and cations can also be made
up of a group of elements bonded
together that carry an overall charge.
•These groups of elements are called
polyatomic ions.
Polyatomic ions - groups of 2
or more elements that have a
charge
NH4+1
PO4-3
SO4-2
NO4-1
ClO3-1
C2H3O2-1
SO3-2
NO3-1
CO3-2
Ionic Compounds
•Even though an ionic compound is
made from charged particles, it is
still electrically neutral.
•This means that its total charge is
always EQUAL TO ZERO!!!
Ionic Compounds
•SIDENOTE: The smallest part of an
ionic compound is called a formula
unit—just like the smallest part of an
element is called an atom.
Chemical Formulas
•A chemical formula is like the recipe
of a compound—it tells you the type
and number of each element in the
compound.
Compounds are written as formulas.
Formula - a group of symbols,
possibly with subscripts, showing
the number and type of atoms
forming the compound.
Na2SO4
Ba3(PO4)2
Formulas consist of a
positive ion and a negative ion.
The positive ion always comes 1st
NaCl
MgO
AlP
The positive ion is written first!!!!!!!!
We read from left to right….
Metals are on the left.
(LEFT = LOSE e- = positively
charged ions)
Metals are first !!!!!
Na+1
Cl-1
Na+1
Cl-1
NaCl
Nonmetals are on the right…
and GAIN e- = negative ions
Nonmetals are second!!!!!
Subscript - a small lowered
number that shows number of
atoms of each element in the
compound.
Ba3P2
Ba Ba
Ba
P
P
A subscript of (1)
is NEVER written.
Na1Cl1
NO!!!
Oxidation number - the charge of
an atom, indicating whether the
atom has lost (+) or gained (-)
electrons and how many electrons it
lost or gained.
Al
+3
Superscript
Oxidation Numbers
Group
Lose or gain
electrons
How many
Oxidation
Number
1A
lose
1
+1
Oxidation Numbers
Group
Lose or gain
electrons
How many
Oxidation
Number
1A
lose
1
+1
2A
lose
2
+2
Oxidation Numbers
Group
Lose or gain
electrons
How many
Oxidation
Number
1A
lose
1
+1
2A
lose
2
+2
3A
lose
3
+3
Oxidation Numbers
Group
Lose or gain
electrons
How many
Oxidation
Number
1A
lose
1
+1
2A
lose
2
+2
3A
lose
3
+3
4A
Lose or gain
4
+4 or -4
Oxidation Numbers
Group
Lose or gain
electrons
How many
Oxidation
Number
1A
lose
1
+1
2A
lose
2
+2
3A
lose
3
+3
4A
Lose or gain
4
+4 or -4
5A
gain
5
-3
Oxidation Numbers
Group
Lose or gain
electrons
How many
Oxidation
Number
1A
lose
1
+1
2A
lose
2
+2
3A
lose
3
+3
4A
Lose or gain
4
+4 or -4
5A
gain
3
-3
6A
gain
2
-2
Oxidation Numbers
Group
Lose or gain
electrons
How many
Oxidation
Number
1A
lose
1
+1
2A
lose
2
+2
3A
lose
3
+3
4A
Lose or gain
4
+4 or -4
5A
gain
3
-3
6A
gain
2
-2
7A
gain
1
-1
Oxidation Numbers
Group
Lose or gain
electrons
How many
Oxidation
Number
1A
lose
1
+1
2A
lose
2
+2
3A
lose
3
+3
4A
Lose or gain
4
+4 or -4
5A
gain
3
-3
6A
gain
2
-2
7A
gain
1
-1
8A
none
none
0
The total charge on a compound
must add up to ZERO.
CaO
+2
Ca
Ca
-2
O
+2 -2 = 0
IONIC
COMPOUNDS
Ionic compounds consist of a
Positive metal or
positive polyatomic ion
Negative nonmetal or
negative polyatomic
ion
Binary compounds are composed
of only two elements.
(Look for 2 capital letters!)
Ex. NaCl
Ex. Mg3N2
sodium chloride
magnesium nitride
Polyatomic compounds are
composed of three or more
elements and contain at
least one polyatomic ion.
(Look for 3 or more capital
letters)
2 3 4
1
NaC2H3O2
Polyatomic ions
Ex. Na ClO3
Ex. Ca3 (PO4)2
sodium chlorate
calcium phosphate
Variable and Non-variable
Metals
(positive ions)
A practical approach to
determining if a metal is variable
or non-variable.
VARIABLE
Look at the chart on the back of
periodic table.
If the metal is on the back of
the periodic table with more
than one oxidation number
listed it is variable.
EX: Cr= +2, +3, or +6
Fe= +2, or +3
Look at the chart on the back of
periodic table.
NON VARIABLE
If it is not on the back of
the periodic table
OR
Only one choice of oxidation number
listed. EX: Ag+1, Zn+2, or Ni+2
Then it is non variable
ROMAN NUMERALS
Used when a metal has more
than one potential oxidation
number.
The name of the metal
must tell you the valence of
the metal
Chromium III chloride
III The Roman numeral
three tells you that
the oxidation number
of the metal is +3.
Chromium VI chloride
VI
The Roman numeral
six tells you that
the oxidation number
of the metal is +6.
Writing and Naming Ionic
Compounds
Writing Chemical Formulas
1) Write the symbol for the elements and their
oxidation number, positive ion first (the
metal).
EX: For a compound of Magnesium and Chlorine
+2
Mg
Cl
-1
Writing Chemical Formulas
2) Criss cross the numbers and write them
as subscripts without the signs.
+2
2
Mg
Cl
-1
1
Writing Chemical Formulas
3) If there is a one charge, do not write it.
Mg1Cl2
Writing Chemical Formulas
4) If you have subscripts that are
multiples, reduce them down.
+4
4
1
-2
2
Pb O2
Naming Ionic Compounds
For ionic compounds where the metal
always has the same oxidation number,
1) Name the metal.
EX: BaBr2
Barium
Naming Ionic Compounds
For ionic compounds where the metal
always has the same oxidation number,
2) Write the name of the non-metal, and
change the end to –ide. EX: BaBr
2
Barium bromine
ide
Naming Binary Non variable
Compounds
1. Name the positive ion
2. Name the negative ion
changing the ending to IDE.
AlBr3
Aluminum bromide
No Roman numeral is needed
-ides
N - Nitrogen--> Nitride
O – Oxygen --> Oxide
F - Fluorine--> Fluoride
P - Phosphorus--> Phosphide
S - Sulfur--> Sulfide
Cl - Chlorine-->Chloride
Br - Bromine -->Bromide
I - Iodine--> Iodide
Naming Polyatomic Non variable
Compounds
1. Name the positive ion
2. Name the negative ion
changing the ending to -ate.
AlPO4
Aluminum Phosphate
No Roman numeral is needed
Naming Ionic Compounds
If there is a polyatomic anion, then you do
not change the ending:
EX: Ca(NO3)2
Calcium nitrate
Name These:
Na2O
MgCl2
Na2CO3
Naming binary compounds
of variable metals
Determine the oxidation number of the
variable metal using the crisscross
method
Cr2O3
Cr+ OThe oxidation number of the
chromium is +3
The name is Chromium III oxide
Naming Ionic Compounds
3)If a positive ion (a metal) can have
more than one oxidation number,
you have to designate its charge in
the name!
We do this by putting the charge as a
roman numeral in parenthesis
between the positive and negative
ion.
Naming Ionic Compounds
Why do we need to do that?
Name:
Fe2O3
FeO
These both exist in nature, so we have
to show which one we mean.
Naming Ionic Compounds
IfReverse
this is true, then
what
+3
criss
was iron to begin with?
Fe-22O3 cross to find the
Name it:
charge of the iron:
Iron (III)oxygen
ide
Naming Ionic Compounds
this
is
not
true,
the
+2 -2 Ifnumbers
Reverse
criss
must have been
Fe-1O cross
reduced.to find the
Name it:
charge of the iron:
Iron ( II )oxygen
ide
Naming Ionic Compounds
Metals that don’t need parentheses:
Group I, II and IIIA
Zn, Cd (always +2) and Ag (always +1)
Which means transition, inner
transition and other metals do!
Naming polyatomic compounds
of variable metals
Determine the valence of the variable
metal using the crisscross method
Hg22SO4
1
Hg+ SO4-
The oxidation number of the
Mercury is +1
Mercury I sulfate
Naming Ionic Compounds
Final flowchart of how to name:
Name the positive ion.
Does it need a roman numeral?
If so, reverse criss cross, if not, ignore.
Name the negative ion and:
If a nonmetal end in -ide; if not, end
normally
Name these:
Na2S
CuCl2
K2SO4
Pb(NO3)3
Finding formulas
1.Determine the charge of each
side of the formula.
Nonvariables:
Aluminum oxide: Al+3 O-2
Potassium Chloride K+1 Cl-1
Calcium nitrate
Ca +2 NO3-1
2. Add the oxidation numbers
together.
+3-2 = +1 +1-1 = 0
+2-1 = +1
2. Add the oxidation numbers
together.
Al+3 O-2
K+1 Cl-1
+3-2 = +1
+1-1 = 0
3. If the total = zero the
formula is balanced with one
ion each ex: KCl
If the total does not equal zero
use the crisscross method to
determine the number of ions
needed for each side of the
formula.
3
Al+3
O-22
Al O
If the total does not equal zero
use the crisscross method to
determine the number of ions
needed for each side of the
formula.
3
2
+3
-2
Al
SO4
Al (SO4)
Writing Chemical Formulas
5) If using polyatomic ions, put
parentheses if there are more than one.
+2
2
-1
1
Ca (NO3)
Writing Chemical Formulas
Here’s an example of a polyatomic that
doesn’t have parentheses.
+1
1
-3
3
Na PO4
Practice These:
Barium and chlorine BaCl
2
Rubidium and nitrogen Rb3N
Lithium and phosphate Li PO
3
4
Iron (III) and nitrate Fe(NO3)3
Manganese (IV) and sulfur MnS2
Chapter 8 Notes: Part III
Bonding in Metals
Metallic Bonds
•Metallic bonds consist of metal
cations with a free-floating “sea of
electrons”
•This explains many physical
properties—why metals are good
conductors, and why they are
malleable and ductile
Malleablilty/Ductility
•Ductile – the ablity to be
drawn into wires
•Malleable – the ablity to
be hammered into shapes
Malleablilty/Ductility
•Metals display these
characteristics because when
subjected to pressure, cations can
easily slide past one another
(unlike ionic solids, which have
very strong attractive and repulsive
forces)
Alloys
•Most metals you use
everyday are a mixture of
two or more elements, for
example brass, bronze or
steel. These are called
alloys.
Alloys
•The importance of alloys
are that often they have
superior properties than
the elements they are
made of.
Oxyanions
An oxyanion is a polyatomic ion
composed of an element, usually a
nonmetal, bonded to one or more
oxygen atoms.
Many oxyaions contain the same
nonmetal and have the same charges
but differ in the number of oxygen
atoms.
These ions are easily named using the
following conventions.
• The ion with more oxygen atoms is
named using the root of the nonmetal
plus the suffix-ate.
• The ion with fewer oxygen atoms is
named using the root of the nonmetal
plus the suffix-ite.
Halogens form four oxyanions
• The ion with the greatest number of oxygen
atoms is named using the prefix per-, the
root of the nonmetal, and the suffix –ate.
• The ion with one less oxygen atom is named
with the root of the nonmetal and the suffix
–ate.
• The ion two fewer oxygen atoms is named
using the root of the nonmetal plus the
suffix –ite.
• The ion with three fewer oxygen atoms
is named using the prefix hypo-, the
root of the nonmetal, and the suffix –
ite.