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NAMING COMPOUNDS AND WRITING FORMULAS
Developed By: Ms. Michelle BurokerModified & 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
Naming Binary Ionic Compounds
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 Name the metal element = cation Sodium
Name the nonmetal by adding the suffix –ide to the root element name
Chloride
CaO
Calcium Oxide
Al2S3
Aluminum Sulfide
MgI2
Magnesium Iodide
What about the transition metals and using Roman Numerals? How does that
work? Let’s see.
FeO 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.
Iron (II) Oxide
Cu2S
Name the first ion. Since it is a transition metal, you must use a Roman Numeral.
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.
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.
Manganese IV oxide
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 We can’t just say Copper oxide. Which one of these is Copper oxide? We must distinguish these by using a Roman Numeral
which is which?
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 namecopper (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
Silver – Ag+1
You need to remember the charges for these!!!
Ag2O Name the first ion.
Silver Name the second ion changing the suffix to –ide.
oxide
ZnCl2 Name the first ion.
Name the second ion changing the suffix to –ide.
Zinc chloride
No Roman Numerals needed for these.
Sometimes you will see the transition elements named using common/traditional names.
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 charges- not so with the Stock system since the Roman numeral tells you the charge.
Remember Transition Metals named with Roman Numerals involve stock names.
Stock name Common NameCopper I Cuprous
Copper II Cupric
Iron II Ferrous
Iron III Ferric
Lead (II) Plumbous
Lead (IV) plumbic
Some Examples
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 subscriptsMagnesium chloride Write the symbol and charge of each ion.
You need a second Cl-1 to balance the charges
The number of each ion (their ratio) tells you the subscripts for each
Mg+2 Cl-1
Cl-1
MgCl2
If only 1 atom then you omit that subscript
More examples:
Iron (III) bromide
Write the symbol and charge of each ion. The charge of the iron is provided by the Roman Numeral.
Fe+3 Br -1
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.
You’ll need three bromide ions to balance the charge (+3) of one iron (III) ion.
Br -1
Br -1
FeBr3
Aluminum Sulfide
Write the symbol and charge of each ion.
Al+3 S-2
Balance the charges by supplying subscripts.
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?
How many sulfurs are needed to arrive at a -6 charge?
2
3
Al+3 S-2
S-2
Al2S3
Naming Ternary Compounds
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:
SO4-2 Sulfate
SO3-2 Sulfite
ClO4-1 Perchlorate
ClO3-1 Chlorate
ClO2-1 Chlorite
ClO-1 Hypochlorite
PO4-3 Phosphate
C2H3O2-1 Acetate
OH-1 Hydroxide
NO3-1 Nitrate
NO2-1 Nitrite
You need to learn these!!!
NH4+1 Ammonium
MnO4-1 Permanganate
How do you recognize Ternary Ionic Compounds?
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 Name the second ion.carbonate
A few more examples:
Fe(OH)3 step 1- Name the first ion.
Iron 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)
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
(III)
step 2- Name the polyatomic ion.
hydroxide
NH4Clstep 1- Name the first ion.
Ammonium
step 2- Name the second ion.
chloride
Notice that since the second ion is a nonmetal as in binary ionic compounds, the suffix of the nonmetal changes to –ide.
(NH4)3PO4step 1- Name the first ion.
step 2- Name the second ion.Ammonium phosphate
ONE more example:
Cu2SO4
step 1- Name the first ion.
Copper
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?
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.
(I) sulfate
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 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.
Write the formula/symbol and charge of each ion.
Al+3 NO3-1
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.
Al(NO3)3
Lead (IV) acetate Write the formula/symbol and charge of each ion.
Pb+4 C2H3O2-1
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
Pb(C2H3O2)4
Calcium phosphateWrite 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
Ca+2 PO4-3
Ca3(PO4)2
Naming Binary Molecular Compounds using Traditional
Nomenclature These compounds
consist of two non-metals 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-
The Rules….
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
Carbon monoxide
N2O4
Dinitrogen tetraoxide
H2O
Dihydrogen monoxide
CCl4
Carbon tetrachloride
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
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?
Writing Formulas for Binary Molecular Compounds using the Traditional Nomenclature Sytem
Very easy to do!!! The prefixes tell you how to write the formulas. example diphosphorus pentoxide
Remembering di = 2 and penta = 5, we get
P2O5Notice that we drop the a from penta when
adding to oxide
Silicon dioxide
Diphosphorous pentachloride
Silicon and oxygen are both nonmetals.
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.SiO2
Phosphorous and chloride are both nonmetals.
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.
P2Cl5
NO
Nitrogen monoxide
Nitrogen and oxygen are both nonmetals.
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 atomstep 2- we calculate the total negative charge -2 x 5 = -10step 3- we know that 2 phosphorus atoms contributed to an offsetting +10 giving us a +5 charge per P atomstep 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 entitiesstep 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 = 10step 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
Naming Binary Acids
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
Hydro-
Stem or root of nonmetal
< NM >
Suffix
-ic Acid
HCl Hydro
HI Hydro
HCl is a binary acid – hydrogen + nonmetal chlorine
chlor ic Acid
iodic Acid
H2S Hydrosulfur ic Acid
Writing Formulas For Binary Acids
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
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
H+1 P-3
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
H3P
Let’s Practice – Reality Check
Ca(OH)2
Calcium hydroxide
SO2
Sulfur dioxide
(NH4)3PO4
Ammonium phosphate
Co2(CO3)3
Cobalt (III) carbonate
HBr
Hydrobromic acid
Ternary Ionic
Binary molecular
Ternary Ionic
Ternary Ionic
Binary acid
Potassium acetate
KC2H3O2
Cadmium nitrate
Cd(NO3)2
Aluminum oxide
Al2O3
Hydrosulfuric acid
H2S
Difluorine trioxide
F2O3
Ternary Ionic
Ternary Ionic
Binary Ionic
Binary acid
Binary molecular
Naming Ternary Acids
These compounds begin with hydrogen since they are “acids”.
Attached to the hydrogen is a polyatomic ion Hydrogen – polyatomic ion examples:
H2SO4
HNO3
H2CO3
Root of polyatomic ion +
suffix
-ic acid
HClO3 Chlor
HNO3Nitr
H2SO4Sulfur
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:
Ternary Acid – contains the polyatomic ion chlorate (suffix= ic) becoming chloricic Acid
ic Acid
ic Acid
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:
Root of polyatomic ion +
suffix
-ous acid
HNO2Ternary acid contains polyatomic ion, nitrite (-ite suffix) becoming nitrous.
Nitr ous acid
HClO2 Ternary acid contains polyatomic ion, chlorite (-ite suffix) becoming chlorous.
Chlor ous acid
H2SO3Ternary acid contains polyatomic ion, sulfite (-ite suffix) becoming sulfurous.
Sulfur ous acid
Writing Formulas for Ternary AcidsFirst, 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 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.
H+1 C2H3O2-1
HC2H3O2
Hypochlorous acid 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 .
H+1 ClO-1
HClO
Phosphoric acid 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” - phosphateH3PO4
Pretend that hydrogen is +1 and balance the charges giving you their combining ratio.
H+1 PO4-3
There You Have It –
NOW for the Secret to Success
PRACTICEPRACTICE
PRACTICEand STILL MORE PRACTICE
That’s All Folks
