Naming Compounds and Writing Formulas

5 types of chemical compounds

•Binary ionic - metal ion – nonmetal ion

•Ternary ionic - at least one ion is a polyatomic ion

•Binary molecular - two nonmetals

•Binary acid - H – nonmetal

•Ternary acid - H – Polyatomic ion

Tips to keep in mind when naming and writing formulas:

Always keep your Periodic Table handy – You should have it in front of you ALWAYS when you are naming and writing formulas.

Remember that metalsmetals (except Hydrogen) are found to the left of the stairstep on the Periodic Table.

NonmetalsNonmetals are found on the right side of the Periodic Table.

Transition MetalsTransition Metals are found from Group 3 to the stairstep (except aluminum which is a regular metal)

How do you name binary ionic compounds? (composed of two elements – a metal and a nonmetal)

•Name the first ion•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.

•Name the second ion changing the suffix to:

–ide.

Examples

NaClName the metal ion

Sodium

Name the nonmetal ion, changing the suffix to –ide.

Chloride

CaO

Calcium

Oxide

Al2S3

Aluminum

Sulfide

MgI2Magnesium

Iodide

BaNa2 You should recognize a problem with this one!This is two metals – not a binary ionic compoundThe name of this is BananaBanana!

What is the name of this compound:

HIJKLMNO?

WATER – “H” to “O”

What about the transition metals and using roman numerals? How does that work?

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.How do you know the charge?

Deductive reasoning.

All compounds are neutral.

Oxygen has a -2 charge (group 16)

Therefore ….. Iron must have a +2 charge since there is one iron and one oxygen. Iron gets a Roman Numeral II.

Iron

IIOxide

Isn’t this easy and FUN!

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 16)

There are two coppers.

Therefore each copper must have a +1 charge for all ions to be neutral

Copper

ISulfide

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

IVoxide

So why must we use Roman Numerals with transition elements?The metals in groups 1, 2, and 13 have single, single, definite charges.definite charges.

Group 1 metals have a +1+1 charge.

Group 2 metals have a +2+2 charge.

Group 13 metals have a +3+3 charge.

Transition metals may have multiple charges – usually two different positive charges.

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

Cu2O

Copper I oxide

Copper is +1

CuO

Copper II oxide

Copper is +2

There are three transition elements which do not require a Roman Numeral because they have single definite charges. These are

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.

Zincchloride

No Roman Numerals needed for these.

Sometimes you will see the transition elements named using common names. Transition metals named with Roman Numerals involves stock 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.

Cuprous = Copper I

Cupric = Copper II

Ferrous = Iron II

Ferric = Iron III

Plumbous = Lead II

Plumbic = Lead IV

There are many more – just be familiar with these six common names.

Stock name Common NameCopper I Cuprous

Copper II Cupric

Iron II Ferrous

Iron III Ferric

Lead (II) Plumbous

Lead (IV) plumbic

In SummaryIn Summary

How do you write formulas for binary ionic compounds given the name?

Two simple steps:

1.Write the symbol and charge of each ion

2.Balance the charges by providing subscripts

Magnesium chloride Write the symbol and charge of each ion.Mg+2 Cl-1

Balance the charges by supplying subscripts. Subscripts tell how many of each atom is present.You need a second Cl-1 to balance the charges

Cl-1

MgCl2

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 supplying subscripts. The subscripts tell how many of each ion is needed to balance the compound.

You’ll need three bromine ions to balance the one iron.

Br -1

Br -1

FeBr3

Aluminum Sulfide

Write the symbol and charge of each ion.Al+3 S-

2Balance the charges by supplying subscripts.In this case the charges do not evenly divide into each other. You must find the least common multiple. 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

Second Category of compounds – Ternary Ionic Compounds. These compounds contain at least one polyatomic ion.

What is a polyatomic ion?

Let’s look at the name to try to understands.

It is an ionion – that means it has a charge.

It is polyatomicpolyatomic – that means it is made of more than one atom.

Simple as that!!

Let’s look at some examples of polyatomic ions.

CO3-2 carbonat

eThis ion is composed of one carbon and three oxygens and the entire group has a charge of -2.Polyatomic ion – Group of atoms that act as a unit

and carry a charge.

More examples:

SO4-2 Sulfate

SO3-2 Sulfite

ClO4-1 Perchlorat

eClO3

-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

(only positive PI)

How do you recognize Ternary Ionic Compounds?

Composed of two ions in which at least one is a polyatomic ion.

There is only one positive polyatomic ion (NH4

+1)

Three possible types of Ternary Ionic Compounds:

•Ammonium + negative ion (nonmetal)

•Metal (positive ion) + negative polyatomic ion

•Ammonium + negative polyatomic ion

Polyatomic Ions

How do you name Ternary Ionic Compounds?

EASY! PIECE OF CAKE! NO PROBLEM!

Name the first ion.

Name the second ion. Isn’t that simple??!!

Examples:

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. CarbonateCarbonate is present here.Name the first ion.

Sodium

Name the second ion.

carbonate

Notice that you do NOT change the suffix – just name the polyatomic ion

A few more examples:

Fe(OH)3 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

Name the polyatomic ion.

hydroxide

NH4Cl Name the first ion.

Ammonium Name the second ion.

chloride

Notice that since the second ion is a nonmetal that, like binary ionic compounds, the suffix of the nonmetal changes to –ide.

(NH4)3PO4Name the first ion.Name the second ion.

Ammoniumphosphate

Looks like a monster, but it’s really simple...

ONE more example:

Cu2SO4

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?

The charge of sulfate is -2.

Since there are two coppers, the charge of the copper must be +1.

I sulfate

Name the second ion.

How do you write formulas for Ternary Ionic Compounds?

Very much like writing formulas for Binary Ionic Compounds.

Two steps:

•Write the formulas/symbols of each ion.

•Balance the charges by supplying subscripts.

•If a subscript is needed for a polyatomic ion, it must be put in parentheses with the subscript on the outside.

Let’s do some!!

Aluminum nitrate

First, you can tell from the name that there is a polyatomic ion present (nitrate). 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 supplying subscripts.

Since Al is +3 and NO3 is -1, you need a total of 3NO3

-1 to balance one Al+3

Since 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 supplying subscripts. Since Pb is +4 and C2H3O2 is -1, you will need 4 C2H3O2

-1 to balance 1Pb+4

Pb(C2H3O2)4

Calcium phosphate

Write the formula/symbol and charge of each ion.

Balance the charges by supplying subscripts. Since Ca is +2 and PO4 is -3, you will need 3 Ca+2 to balance 2 PO4

-3

Ca+2 PO4-3

Ca3(PO4)2

The Third Category of Compounds – Binary Molecular

What are Binary Molecular Compounds?

These compounds contain two elements (binary).

The term “molecular” indicates that these elements are joined by a covalent bond.

They must therefore be nonmetals.

Bottom line – 2 elements – both nonmetals

To name and write formulas for these, you must know some numerical prefixes.

Naming – you must use prefixes.

1 = mono 3 = tri 5 = penta 7 = hepta 9 = nona

2 = di 4 = tetra 6 = hexa 8 = octa 10 = deca

Steps

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.

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.Do you think it

wise to BAN DHMO?

AlCl3 What do you think about this one???

Be careful. This is a metal and nonmetal.

Always keep your Periodic Table in front of you for reference.

You may have been tempted to say “aluminum trichloride”. This is INCORRECT!

This is a binary IONIC compound. No prefixes are used. Simply aluminum chloride.

Given the names of binary molecular compounds, how do you write the formulas?

Very easy to do!!! The prefixes tell you how to write the formulas. DO NOT CONSIDER CHARGES. NONMETALS ARE ALL NEGATIVE SO TO USE CHARGES DOES NOT WORK!

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 phosphorouses (Is that a word?)

The prefix “penta” before chlorine means that there are five chlorines.

P2Cl5

NO

Nitrogen monoxideNitrogen and oxygen are both nonmetals.

The lack of a prefix on nitrogen means only ONE nitrogen.

The prefix “mono” on oxygen indicates ONE oxygen.Is this not sooooooo easy!??

What are Binary Acids?

Binary means two elements

Acid means it contains hydrogen

The second element is a nonmetal

hydrogen – nonmetal

Naming

All binary acids follow the pattern as shown below:

Prefix

Hydro-

Stem or root of nonmetal

< NM >

Suffix

-ic Acid

HCl Hydro

HI Hydro

HCl is a binary acid – hydrogen - nonmetal

chloric Acid

iodic Acid

H2S Hydrosulfur

ic Acid

Given the name, how do you write 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 supplying subscripts.Hydrofluoric Acid

The name tells you that this is a binary acid.H+1 F-1

HF

Hydrophosphoric acid

The name tells you that it is definitely a binary acid.

H+1 P-3

Remember that the P has a -3 charge because it is in group 15

H3P

Let’s Practice

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

The fifth category of compounds is Ternary Acids.

These compounds begin with hydrogen since they are “acids”.

Attached to the hydrogen is a polyatomic ion

Hydrogen – polyatomic ion

<Root of polyatomic ion>

suffix

-ic acid

HClO3 ChlorHNO3Nitr

H2SO4 Sulfur

HCN Cyan

How are Ternary Acids named?There are two categories of naming depending on the suffix of the polyatomic ion.

First CategoryFirst Category: If the polyatomic ion has a suffix of –ate or –ide, use the following pattern:

Ternary Acid – contains the polyatomic ion chlorate (suffix –ate)

Ternary Acid – contains the polyatomic ion nitrate (suffix –ate).

Ternary Acid – contains the polyatomic ion sulfate (suffix –ate).

Ternary Acid – contains the polyatomic ion cyanide (suffix –ide).

icAcid

ic Acidic Aci

dic Aci

d

Second Category: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).

Nitrous acid

HClO2 Ternary acid contains polyatomic ion, chlorite (-ite suffix).

Chlorous acid

H2SO3Ternary acid contains polyatomic ion, sulfite (-ite suffix).

Sulfurous acid

How are Ternary Acids named?

First, a ternary acid is easy to distinguish from a binary acid.

ALL binary acids have the prefix “hydro-”.

NO Ternary acids have the prefix “hydro-”.

Acetic acid

This is an acid, but NOT a binary acid.

This is a ternary acid.

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-”.

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.

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” - phosphate

H3PO4

Pretend that hydrogen is +1 and balance the charges.