Naming Compounds and Writing Formulas

Report
Developed By: Ms. Michelle Buroker
Modified & Expanded By: Dr. Rick Moleski
5 Types of Chemical Compounds
(Based on Type of Bond)
Binary ionic - metal ion – nonmetal ion
Ternary ionic - at least one ion is a
polyatomic ion (either cation or
anion)
Binary molecular - two nonmetals
Binary acid - H +1 – nonmetal
Ternary acid - H +1– Polyatomic ion
STEP 1:
•
•
Name the first ion (cation)
If the first ion is a transition element other than
zinc, cadmium, or silver, you must use a Roman
Numeral with the name – we’ll discuss this later.
You check the Periodic Table for the charge• Column 1 = 1 valence electron = +1 charge
• Column 2 = 2 valence electrons = +2 charge
• Column 13 = 3 valence electrons = + 3 charge
STEP 2:
Name the second ion (anion)
changing the suffix to –ide.
Examples
NaCl
Sodium Chloride
Name the metal
element = cation
CaO
Calcium
Oxide
Al2S3
Aluminum Sulfide
MgI2
Magnesium Iodide
Name the nonmetal by
adding the suffix –ide
to the root element
name
What about the transition metals and
using Roman Numerals? How does that
work? Let’s see.
FeO
Iron (II) Oxide
Notice – metal and nonmetal.
Name the first ion. Since the first ion is a transition
element, you must use a Roman Numeral to
represent the charge. Exceptions Zn (+2) Ag (+1) Cd (+2)
How do you know the charge?
Deductive reasoning.
All compounds are neutral.
Oxygen has a -2 charge (Column 16, group 6A)
Therefore ….. Iron must have a +2 charge since
there is one iron and one oxygen. Iron gets a Roman
Numeral II.
Name the first ion. Since it is a transition metal, you
must use a Roman Numeral.
Cu2S
Which Roman Numeral? The Roman Numeral is the
same as the charge of the ion.
How do you find the charge?
Deductive reasoning!
All compounds are neutral
Sulfur has a -2 charge (group 6A)
There are two coppers.
Therefore each copper must have a +1 charge for all
ions to be neutral
Copper I Sulfide
Another Example: MnO2
Name the first ion. Since it is a transition metal,
you must use a Roman Numeral.
Manganese IV oxide
How do you determine the Roman Numeral?
It is the same as the charge.
What is the charge of Mn?
All compounds are neutral.
Oxygen (group 16) has a -2 charge.
There are two oxygens and one Mn.
Therefore Mn must have a +4 charge for this
compound to be neutral.
So why must we use Roman Numerals with
transition elements?
The metals in groups 1A, 2A, and 3A have single, definite charges or
referred to as being monovalent
Column 1, Group 1A metals have a +1 charge.
Column 2, Group 2A metals have a +2 charge.
Column 13, Group 3A metals have a +3 charge.
Transition metals may have multiple charges – usually two different
positive charges. They are referred to as being multivalent
For example, there are two copper oxide compounds:
Cu2O and CuO
which is which?
We can’t just say Copper oxide. Which one of
these is Copper oxide? We must distinguish these
by using a Roman Numeral
The solution lies with the negative ion or nonmetal’s charge which
are always related back to the number of valence electrons and
hence their oxidation number:
Column 17, group 7A has a -1 charge (due to 7 valence e-)
Column 16, group 6A has a -2 charge (due to 6 valence e-)
Column 15, group 5A has a -3 charge (due to 5 valence e-)
Given CuO we know that there is a -2 charge per O atom and since
there is only one O atom the total negative charge is -2 and must
be offset by a +2 charge; because there is only copper atom it has
to have a +2 charge or oxidation number giving us the name
copper (II) oxide
From a bonding perspective, the -2 charge of the O atom
represents the acquisition of 2 electrons. These two electrons came
from the copper atom and would represent the lose of 2 electrons
The other form of “copper oxide” has the formula Cu2O
To determine its name we use the same approach:
Oxygen has a -2 charge per atom and since there is only one
atom the total negative charge is -2 (12 charge/ atom x 1 atom = -2)
Therefore the offsetting positive charge has to have a total
positive charge of +2 and since this charge is from 2 atoms of
copper, each has a +1 charge (+2 total charge ÷ 2 atoms = +1 charge
per atom)
This gives us an charge or oxidation number of +1 and a
Roman numeral of (I)
Name: copper (I) oxide
There are three transition elements which do not
require a Roman Numeral because they have single
definite charges.
Zinc – Zn+2
Cadmium – Cd+2
You need to remember the
charges for these!!!
Silver – Ag+1
Ag2O
Name the first ion.
Silver oxide
Name the second ion changing the
suffix to –ide.
ZnCl2
Name the first ion.
Zinc chloride
Name the second ion changing the
suffix to –ide.
No Roman
Numerals
needed for
these.
The common names use the Latin derivative of the
element’s name with a suffix of either –ous or –ic.
The –ous suffix name corresponds with the smaller
charge.
The –ic suffix name corresponds with the larger charge.
With the traditional names using the different suffixes,
you had to memorize both the name and the chargesnot so with the Stock system since the Roman numeral
tells you the charge.
Remember Transition Metals named with Roman
Numerals involve stock names.
Some Examples
Stock name
Common Name
Copper I
Cuprous
Copper II
Cupric
Iron II
Ferrous
Iron III
Ferric
Lead (II)
Plumbous
Lead (IV)
plumbic
How do you write formulas for
binary ionic compounds given the
name?
Three simple steps:
1. Write the symbol and charge of each ion
2. Balance the charges by adjusting number of ions
3. Based on the ratio apply the necessary subscripts
Magnesium chloride
Write the symbol and charge of each ion.
Mg+2
You need a second Cl-1 to balance the
charges
Cl-1
Cl-1
MgCl2
If only 1 atom then you
omit that subscript
The number of each ion (their ratio) tells
you the subscripts for each
More examples:
Iron (III) bromide
Br -1
Br -1
Br -1
Write the symbol and charge of each ion.
The charge of the iron is provided by the
Roman Numeral.
FeBr3
Balance the charges by adjusting the
number of ions; this becomes the
subscripts. The subscripts tell how many
of each ion is needed to balance the
compound.
Fe+3
You’ll need three bromide ions to balance
the charge (+3) of one iron (III) ion.
Write the symbol and charge of each ion.
Balance the charges by supplying subscripts.
Aluminum Sulfide
Al+3
Al+3
S-2
S-2
S-2
In this case the charges do not evenly divide
into each other. You must find the least
common multiple (LCM). SIX
How many aluminums are needed to arrive at
a +6 charge?
2
Al2S3
How many sulfurs are needed to arrive at a -6
charge?
3
These compounds contain at least one polyatomic ion.
What is a polyatomic ion?
Let’s look at the name to try to understand.
It is an ion – that means it has a charge.
It is polyatomic – that means it is made of more than
one atom.
Let’s look at some examples of polyatomic ions
CO3
-2
carbonate
This ion is composed of one carbon and
three oxygens and the entire group has a
charge of -2.
Polyatomic ion – Group of covalently bonded atoms that carry an
electrical charge and act as a unit during reactions, that is, the atoms
stay bonded together. More examples:
MnO4-1
SO4-2
Sulfate
SO3-2
Sulfite
ClO4
-1
Perchlorate
PO4-3
C2H3O2-1
Permanganate
Phosphate
Acetate
OH-1
Hydroxide
NO3-1
Nitrate
ClO3-1
Chlorate
Nitrite
ClO2-1
NO2-1
Chlorite
Hypochlorite
NH4+1
Ammonium
ClO-1
You need to learn these!!!
You see more than two element symbolized in the
chemical formula
Composed of two ions in which at least one is a
polyatomic ion.
There is only one common positive polyatomic ion,
ammonium (NH4+1), that forms a compound
How do you name Ternary Ionic Compounds?
EASY! PIECE OF CAKE! NO PROBLEM!
1) Name the first ion.
2) Name the second ion.
Na2CO3
When you look at this compound you should
recognize that this is NOT binary. There are
THREE elements present. When you see this,
immediately look for a polyatomic ion.
Carbonate is present here.
Name the first ion.
Sodium carbonate
Name the second ion.
A few more examples:
Fe(OH)3
Iron (III) hydroxide
Since there are 3
OH groups, each
with a -1 charge, the
charge of the iron
must be +3 for the
compound to be
neutral
step 1- Name the first ion.
Remember that iron requires a Roman Numeral
since it is a transition element. What Roman
Numeral should be used?
The Roman Numeral comes from the charge of
the ion. How do you find the charge of the iron?
You know two things:
•All compounds are neutral.
•You know the charge of OH (-1)
step 2- Name the polyatomic ion.
NH4Cl
step 1- Name the first ion.
step 2- Name the second ion.
Ammonium chloride
Notice that since the second ion is a nonmetal as in binary ionic
compounds, the suffix of the nonmetal changes to –ide.
step 1- Name the first ion.
(NH4)3PO4
Ammonium
phosphate
step 2- Name the second ion.
ONE more example:
Cu2SO4
step 1- Name the first ion.
You should realize that you need a Roman
Numeral since copper is a transition metal.
The Roman Numeral is the same as the
charge.
What is the charge?
Copper (I) sulfate
Working backwards - the charge of sulfate is a
-2 per polyatomic ion and there’s only 1
giving us a total of -2.
The plus charge must offset the -2 giving us a
total plus charge of+2 Since there are two
coppers, the charge per copper ion must be
+1.
step 2- Name the second ion.
How do you write formulas for Ternary
Ionic Compounds?
Very much like writing formulas for Binary Ionic Compounds.
Three steps:
•Write the formulas/symbols of each ion.
•Balance the charges by adjusting the number of ions
•From the resulting ratio apply subscripts equal to the
number of ions.
•If a subscript is needed for a polyatomic ion, it must be put
in parentheses with the subscript on the outside.
Aluminum nitrate
Al+3
NO3-1
First, you can tell from the name that there is
a polyatomic ion present (nitrate). Remember
that all binary ionic compounds have suffixes
of –ide.
Al(NO3)3
Write the formula/symbol and charge of each ion.
Balance the charges by adjusting the number of ions and those
numbers (ratio) become the subscripts in the formula.
Since Al is +3 and NO3 is -1, you need a total of 3NO3-1 to
balance one Al+3
You will need a subscript of 3 for NO3-1; you need to put this in
parentheses with the 3 outside.
Lead (IV) acetate
Pb+4
C2H3O2-1
Pb(C2H3O2)4
Calcium phosphate
Ca+2
PO4-3
Ca3(PO4)2
Write the formula/symbol and charge of each
ion.
Balance the charges by adjusting the number of
ions and this number becomes the subscripts.
Since Pb is +4 and C2H3O2 is -1, you will need
4 C2H3O2-1 to balance 1Pb+4
Write the formula/symbol and charge of each
ion.
Balance the charges to determine subscripts.
Use the LCM of 6. Since Ca is +2 and PO4 is a
-3, you will need 3 Ca+2 to balance 2 PO4-3
These compounds
consist of two nonmetals and to name
them, you need to
know the following
prefixes:
1
Mono-
2
Di-
3
Tri-
4
Tetra-
5
Penta-
6
Hexa-
7
Hepta-
8
Octa-
9
Nona-
10
Deca-
1.
The first nonmetal only gets a numeric prefix when
there is more than one. No prefix if there is only
one.
2.
The second element always gets a numeric prefix
and always has a suffix of -ide
CO2
Carbon dioxide
CO
Name the first element. Since there is only
one, no prefix is needed. The second element
always gets a prefix and a suffix of –ide.
examples are CO2 and CO
Carbon monoxide
N2O4
Dinitrogen tetraoxide
H 2O
Dihydrogen monoxide
CCl4
Carbon tetrachloride
Name the first element. Since there
are two present, the prefix “di” is
needed. The second element always
gets a prefix and a suffix of –ide.
examples are N2O4 and H2O
Why do we use the prefix tetra
for the name of CCl4?
Very easy to do!!! The prefixes tell you how to write
the formulas. example diphosphorus pentoxide
Remembering di = 2 and penta = 5, we get
P2O5
Notice that we drop the a from penta when adding to
oxide
Silicon and oxygen are both nonmetals.
Silicon dioxide
SiO2
The lack of a prefix on silicon means that there
is only ONE silicon.
The prefix “di” in front of oxide means that
there are TWO oxygens.
Diphosphorous pentachloride
Phosphorous and chloride are both nonmetals.
P2Cl5
The prefix “di” means that there are TWO atoms of
phosphorous covalently bonded to the chlorines
The prefix “penta” before chlorine means that there
are five chlorines.
Nitrogen and oxygen are both
nonmetals.
Nitrogen monoxide
NO
The lack of a prefix on nitrogen means
only ONE nitrogen.
The prefix “mono” on oxygen indicates
ONE oxygen.
But wait these nonmetal molecular compounds
can be written using the Stock System
Naming Molecular Compounds
using the Stock System
This system uses Roman Numerals that indicate the oxidation
number of the first nonmetal in the formula. This is similar to
what we did with the transition metals; for example P2O5
step 1- we assign a charge value of -2 per Oxygen atom
step 2- we calculate the total negative charge -2 x 5 = -10
step 3- we know that 2 phosphorus atoms contributed to
an offsetting +10 giving us a +5 charge per P atom
step 4- write the name of the first element followed by
the Roman numeral for 5 in parenthesis
step 5- use the –ide form of the second nonmetal’s name
phosphorus (V) oxide
Writing Nonmetal Molecular
Formulae using Stock System
Since the name tells you the charge per atom of the first nonmetal,
you follow these steps using sulfur (VI) oxide as our example:
step 1- determine the charge of the second nonmetal from its
position on the Periodic Table- -2 charge/O atom (column 17)
step 2- figure out how many oxygen atoms are needed to
equal a charge of -6 since you know that sulfur is a +6; 3 O
step 3- from the ratio write the formula; 1S:3O = SO3
Another example: phosphorus (V) oxide Let’s see what you can do
step 1- using the -2 oxidation number (charge) for an oxygen atom
we know that it will not go into 5 as a whole number which is
needed since atoms do not exist as fractional entities
step 2- the remedy is to find the LCM (lowest common multiple)
of both +5 (from the Roman numeral in the name) and -2 (found in
the previous step) – lcm is found by multiplying the two charge
numbers without regard for sign together 5 x 2 = 10
step 3- divide 10 by both charges resulting in the ratio of atoms
P: 10 ÷ 5 = 2
O: 10 ÷ 2 = 5
Ratio 2P:5O
step 4- write the formula using the ratio as the required subscripts
P2O5
Remember that acids always begin with an “H” in
their formula and are aqueous solutions
So, what is a binary acid?
Binary Acids are those which contain hydrogen and
a non-metal element.
Naming them requires a prefix and a suffix added to
the root of the nonmetal element and the word
“acid” added afterwards
Prefix
Stem or root of
nonmetal
Suffix
Hydro- < NM > -ic
Acid
HCl is a binary acid – hydrogen + nonmetal chlorine
HCl
Hydro chlor ic Acid
HI
Hydro iodic Acid
H2S
Hydro sulfur ic Acid



The obvious pattern of the name tells you that it is a
binary acid. Hydro<NM>ic Acid.
Therefore, you know that the acids begins with
hydrogen and contains a nonmetal which you can
identify between the “Hydro” and the “ic”
To arrive at the formula, you “pretend” that
hydrogen is +1 and using the normal charge of the
nonmetal, balance the formula by adjusting their
number of atoms thereby determining the subscripts.
Hydrophosphoric acid
The name tells you that it is definitely a
binary acid. How? The hydro prefix
H+1
P-3
H3 P
step 1- you find the oxidation number for
phosphorus from the Periodic Table (P = -3)
step 2- determine how many “H” you need
at a “+1” to equal -3; answer 3
step 3- write the formula using the above
ratio for the number of each element
Remember that the P has a -3 charge because it is in Column 15 (group
5A) thereby signifying 5 valence electrons and a -3 charge when stable
Let’s Practice – Reality Check
Ca(OH)2
Ternary Ionic
Calcium hydroxide
SO2
Binary molecular
Sulfur dioxide
(NH4)3PO4
Ammonium phosphate
Ternary Ionic
Co2(CO3)3
Cobalt (III) carbonate
Ternary Ionic
HBr
Hydrobromic acid
Binary acid
Potassium acetate
Ternary Ionic
KC2H3O2
Cadmium nitrate
Ternary Ionic
Cd(NO3)2
Aluminum oxide
Binary Ionic
Al2O3
Hydrosulfuric acid
Binary acid
H2S
Difluorine trioxide
F2O3
Binary molecular

These compounds begin with hydrogen since they
are “acids”.

Attached to the hydrogen is a polyatomic ion

Hydrogen – polyatomic ion

examples:
 H2SO4
 HNO3
 H2CO3
How are Ternary Acids named?
There are two categories of naming depending on the
suffix of the polyatomic ion.
First Category: If the polyatomic ion has a suffix of –
ate, use the following pattern:
suffix
Root of polyatomic ion + -ic
HClO3
HNO3
H2SO4
Chlor ic Acid
Nitric Acid
Sulfur ic Acid
acid
Ternary Acid – contains the polyatomic ion
chlorate (suffix= ic) becoming chloric
Ternary Acid – contains the polyatomic ion
nitrate (suffix= ic) becoming nitric
Ternary Acid – contains the polyatomic ion
sulfate (suffix= ic) becoming sulfuric
Second Category: If the polyatomic ion has a suffix
of –ite, use the following pattern:
suffix
Root of polyatomic ion + -ous
HNO2
Nitr ous
HClO2
Chlor ous
H2SO3
Sulfur ous
acid
Ternary acid contains polyatomic ion,
nitrite (-ite suffix) becoming nitrous.
acid
acid
acid
Ternary acid contains polyatomic ion,
chlorite (-ite suffix) becoming chlorous.
Ternary acid contains polyatomic ion,
sulfite (-ite suffix) becoming sulfurous.
Writing Formulas for Ternary Acids
First, a ternary acid is easy to distinguish from a binary acid.
ALL binary acids have the prefix “hydro-”.
Most Ternary acids have the prefix “hydro-” but a few do like HCN
which is hydrocyanic acid- the exceptions are simply memorized.
Acetic acid
H+1 C2H3O2-1
HC2H3O2
This is an acid, but NOT a binary acid; it’s Ternary
Will begin with an “H” followed by the corresponding
polyatomic ion
The “-ic” suffix in the acid name tells you that the
polyatomic ion must have a “-ate” suffix – acetate.
To write the formula, pretend that hydrogen is +1 and
balance the charges.
Hypochlorous acid
H+1
ClO-1
HClO
This is a Ternary acid (does not begin with
“hydro-”; although “hypo” it’s not the same).
The “-ous” suffix indicates that the
polyatomic ion in this acid has a suffix of “ite” - hypochlorite
Pretend that hydrogen is +1 and balance the
charges giving you their combining ratio.
Phosphoric acid
H+1
PO4-3
H3PO4
This is a Ternary acid (does not begin with
“hydro-”).
The “-ic” suffix indicates that the polyatomic
ion in this acid has a suffix of “-ate” phosphate
Pretend that hydrogen is +1 and balance the
charges giving you their combining ratio .
NOW for the Secret to Success
PRACTICE
PRACTICE
PRACTICE
and
STILL MORE PRACTICE

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