NOTE: 

this page is being updated and is currently under construction.  Where it is black, it is finished.  In the meantime, the info on this page is all available on the formula and nomenclature handout at this link: 

CHEM 151 Formula and Nomenclature

Please study that and contact the instructor or the Learning Commons tutors for questions or help.

Common elements and their symbols

You are not expected to know the names and symbols of all the elements on the periodic table, but you are expected to know the names, symbols, and correct spelling of the elements that are most commonly encountered (either in their pure form or as parts of compounds).  These elements are listed below.  Knowing these will make it much easier to name and recognize formulas of compounds, which will be covered next.

Table of common elements and their symbols

hydrogen	H
helium	He
lithium	Li
boron	B
carbon	C
nitrogen	N
oxygen	O
Fluorine (NOT Flourine)	F
neon	Ne
sodium	Na
magnesium	Mg
aluminum	Al
silicon	Si
phosphorus (ends in us, not -ous)	P
sulfur	S
chlorine (not clorine)	Cl
argon	Ar
potassium	K
calcium	Ca
chromium	Cr
manganese	Mn
iron	Fe
cobalt	Co
nickel	Ni
copper	Cu
zinc	Zn
bromine	Br
strontium	Sr
palladium	Pd
silver	Ag
tin	Sn
iodine	I
barium	Ba
platinum	Pt
gold	Au
mercury	Hg
lead	Pb
uranium	U

Naming Compounds

Compounds are pure substances that contain more than one element. Different classes of compounds that you will learn about in this course have different rules for naming.  Right now, the rules might not make sense but as you progress through the course they will make more sense.  Learning the rules now will help you better identify names and compounds throughout the course.  It will also make it easier for you to learn and understand concepts and differences about the different classes of compounds you will encounter in chemistry and much of science.

Sections 1 and 2. Binary Compounds

The first class of compounds we will look at are binary compounds.  The number two is associated with the word binary, and binary compounds are compounds that contain two elements.

Before you can properly name binary (or any other types) of compounds, you must understand that elements are divided into two major categories: metals and non-metals.

Figure 2.26 in OpenStax Chemistry 2e illustrates the difference between the metals and non-metals (see the color coding next to the table).

The metalloids (in purple)are between the metals and nonmetals and have properties of both.  The only metalloid you will be responsible for in naming is Si, which you can consider to be a nonmetal.

Binary compounds can either be made of of two nonmetal elements or one metal and one nonmetal element (there are no binary compounds made up of two metals).  The rules for naming them are different (as shown in the next two sections) because the way they are formed and bonded are different (as you will learn later in the course).

Section 1. Binary Compounds Composed of Two Nonmetals

Binary compounds composed of two nonmetals are named using the elemental name for the first element followed by the name of the second element with its ending changed to “IDE“. Two examples of binary compounds that you very likely have heard of are:

CO – carbon monoxide

CO₂ – carbon dioxide

In binary compounds with two nonmetals, different amounts of the first element can be in a compound with different amounts of the second element.  A molecule of carbon monoxide contains one carbon atom and one oxygen atom (1:1 ratio).  A molecule of carbon dioxide contains one carbon atom and two oxygen atoms (1:2 ratio).  For that reason, to differentiate between the various compounds a prefix is added to indicate the number of atoms of each element in the molecule.

Table Listing the Proper Prefix for a Given Numbers of Atoms

Number of atoms in formula	Prefix
1	mono
2	di
3	tri
4	tetra
5	penta
6	hexa
7	hepta
8	octa
9	nona
10	deca

Example:

S₂F₁₀

1. Since S and F are both nonmetal elements, the naming rules in this section are used.
2. Use the elemental name for the first element S: sulfur
3. since there are two sulfur atoms, the prefix is di: disulfur
4. The root of the second element name “fluor” from fluorine is followed by ide: fluoride
5. Since there are ten F atoms, the prefix is deca: decafluoride.
6. The name for S₂F₁₀ is disulfur decafluoride

There are two idiosyncancies or minor exceptions to these naming rules:

1. The mono prefix is eliminated if it refers to the first element in the name.  If you think about it, you are probably already aware of this.  Most students have heard of the compound carbon dioxide, CO₂. I suspect you have heard of it as well.But you probably have not heard of “monocarbon dioxide”  – that’s because the initial mono is not included.

2. For oxides, the prefixes ending in “a” and “o” omit the last vowels, to avoid having two consecutive vowels.  There is a familiar example to help you remember this as well: CO is carbon monoxide, not carbon monooxide.  Another example is N₂O₄: dinitrogen tetroxide, not dinitrogen tetraoxide.

Note that the “i” in di and tri would not be eliminated in oxides – as you know, CO₂ is carbon dioxide (not carbon doxide)

Here are more examples:

Formula	Name
NO2	nitrogen dioxide
CO	carbon monoxide
P4O10	tetraphosphorus decoxide
CS2	carbon disulfide

As discussed earlier, the “a” in decoxide and “o” in monoxide are omitted.  Note that the “i” in di and tri would not be eliminated in oxides

Practice – Binary Compounds Composed of Two Nonmetals

Drill 1.1

Please name the following compounds. Correct spelling is required.

1. SO₂
2. CCl₄
3. P₂O₅
4. ClO
5. ICl
6. SF₆

Drill 1.2

Please write the correct chemical formulas.

1. dichlorine heptoxide:
2. dinitrogen pentoxide:
3. oxygen difluoride:
4.  phosphorus pentachloride:

Link to answers to drills

 

Section 2. Binary Salts (Compounds Composed of a Metal and a Nonmetal)

These compounds are named differently than binary compounds because they are fundamentally different on how the elements combine to make the compounds.  Here are some examples of how they are named differently:

ICl (binary with two nonmetals) is iodine monochloride, but NaCl (made up of the metal sodium and the nonmetal chlorine) is sodium chloride (NOT sodium monochloride)

SCl₂ (binary with two nonmetals) is sulfur dichloride, but CaCl₂ (made up of the metal calcium and the nonmetal chlorine) is calcium chloride (NOT calcium dichloride).

As shown above, prefixes like mono-, di- and tri- are NOT used in binary compounds made up of a metal and a nonmetal.  Next, we will look at how these compounds are different, how we know the ratio of elements without the prefixes, and more about these compounds.

Covalent and Ionic Bonding in compounds

We are working a little ahead – the concept of covalent and ionic bonding will be studied later in the course.  But we’ll start with the basics now so you have a little background for these two types of compounds, at least as they pertain to binary compounds.

Compounds consisting of all nonmetals (like the ones studied in the previous section) are covalently bonded and exist as molecules.   For example, a molecule of carbon dioxide, CO₂, consists of one C atom and two O atoms.  The smallest amount of carbon dioxide possible is one molecule consisting of three atoms (one carbon and two oxygen).  If you had a tank filled with CO₂, it would be filled with a large number of these molecules, each separate from each other.

Ionic compounds are different.  Rather than existing as separate molecules, they typically exist in repeating structures called crystal lattices.  For example, cesium chloride (CsCl) consists of a repeating structure with a ratio of one Cs to one Cl.  It does not exist as separate molecules, each with one Cs atom and one Cl atom.  Figure 10.59 in OpenStax illustrates this (See the figure to the right):

 

The structure of CaCl₂ would be a similarly repeating structure, except with a 1:2 ratio of Ca to Cl.  Metals only pair with nonmetals in certain ratios (Ca and Cl only pair 1:2, for example), so prefixes are not needed or used.  So how do we know the ratio?  We will look at that next.

The metals and nonmetals in binary salts are ions.

An ion is an atom with a charge (to learn more about atoms and ions, go to this section of the course: Atoms, Molecules, and Ions).  The metal has a positive charge and is called a cation, while the nonmetal has a negative charge and is called an anion.

The charge is listed as a superscript next to the element symbol as follows:

• Na is a neutral (charge = 0)  sodium atom
• Na⁺ is a sodium ion with a charge of +1
• Ca is a neutral (charge = 0)  calcium atom
• Ca²⁺ is a sodium ion with a charge of +2
• O is a neutral (charge = 0)  oxygen atom
• O^2- is a sodium ion with a charge of -2

Different elements typically have different charges.  You should recognize and know that the elements ionic charges are the ones listed below.

Common cations (positive)

From Group 1 (first column) in the periodic table

Element	symbol (including charge)
hydrogen	H+
lithium	Li+
sodium	Na+
potassium	K+

From Group 2 (second column) in the periodic table

Element	symbol (including charge)
magnesium	Mg2+
calcium	Ca2+
strontium	Sr2+
barium	Ba2+

From Group 3 in the periodic table

Element	symbol (including charge)
aluminum	Al3+

Other common cations, not related to column in the periodic table

Unfortunately, these must be memorized.  Also, some elements (copper, iron, and others have more than one common ionic charge.  Roman Numerals as shown in the table below are used to distinguish metals that tend to form two or more common ions of different charge.

Element	symbol (including charge)
Silver	Ag+
copper(I)	Cu1+
copper(II)	Cu2+
iron(II)	Fe2+
iron(III)	Fe3+
mercury(I)	Hg22+
mercury(II)	Hg2+
lead(II)	Pb2+
lead(IV)	Pb4+
nickel	Ni2+
tin(II)	Sn2+
tin(IV)	Sn4+
zinc	Zn2+

Common anions (negative)

When looking at the tables below, you will see that there is an extra column in the anion tables with an ion name ending in “-ide”.  The anions have these names.

• The name of a metal cation ion is generally the same as the name of the element.
• Nonmetal ions are named by changing the ending of the element name to “ide“.

For example,

Na⁺ is the sodium ion (cations do not have the -ide name, while Cl^– is the chloride ion.

From Group 7 (next to right column) in the periodic table

Element	symbol (including charge)	Ion Name
fluorine	F―	fluoride
chlorine	Cl―	chloride
bromine	Br―	bromide
iodine	I―	iodide

From Group 6 (left of Group 7) in the periodic table

Element	symbol (including charge)	Ion Name
oxygen	O2―	oxide
sulfur	S2―	sulfide

From Group 5 (left of group 6) in the periodic table

Element	symbol (including charge)	Ion Name
nitrogen	N3―	nitride
phosphorus	P3―	phosphide

From Group 4(left of group 5) in the periodic table

Element	symbol (including charge)	Ion Name
carbon	C4―	carbide

And one more…..

Element	symbol (including charge)	Ion Name
hydrogen	H―	hydride

Naming Binary Salts

In both name and formula, the metal cation always comes first.  Therefore, the binary salt compound made up of sodium and chlorine is:

NaCl.  The name is sodium chloride.  That is why the anions have the -ide name to their ending — NaCl (sodium chloride) is made up of the sodium ion (Na⁺) and the chloride ion (Cl^–).

NaCl is NOT ClNa or chlorine sodiumide.

Also, notice NaCl is sodium chloride.  It is NOT sodium monochloride.  That is because NaCl is the only binary compound made up of sodium and chlorine.  NaCl exists.  NaCl, NaCl₂, Na₂Cl,NaCl₃,NaCl₄, etc do not.  For that reason, using prefixes mono, di, tri, etc is unnecessary (and incorrect) for metal-nonmetal binary salts.

How then, do we know sodium chloride is NaCl and vice-versa?  Metal ions are combined with nonmetal ions such that the sum of the positive and negative charges is zero resulting in overall neutral compounds.  Let’s look at some examples:

Example 1:  Sodium chloride:

Consider the charges on the constituent elements’ ions.  Place the element with the positive charge first followed by the element with the negative charge.

The charge on the sodium ion is +1 and the charge on the chloride ion is 1^―.  Each sodium will cancel out each chlorine and NaCl will have a 1:1 ratio of cations to anions.

The correct formula for electrically neutral sodium chloride is therefore NaCl.

Example 2:  Magnesium chloride.

• The charge on the magnesium ion is +2 and the charge on the chloride ion is 1^―.  Each magnesium ion will cancel out two chloride ions and there will be a 1:2 ratio of cations to anions.The correct formula for electrically neutral sodium chloride is therefore MgCl₂.  It is NOT magnesium dichloride.

Mg2+	+	2Cl―	=	MgCl2
+2	+	2(―1)	=	0

 

  Example 3:  Aluminum oxide.

• The charge on the aluminum ion is 3+
• The charge on the oxide ion is 2^―.

AlO cannot be the correct formula because +3 and +2 does not equal zero. However,

• 2 aluminum ions (Al³⁺) would give a total of 6 positive units
• 3 oxygen ions (O^2-) would give 6 negative units.

2Al3+		3O2―	=	Al2O3
2(+3)		3(―2)	=	0

The correct simplest formula for aluminum oxide is Al₂O₃.

More examples

Li₃N – lithium nitride

KBr  –    potassium bromide

CaI₂   –   calcium iodide

Practice – Binary Compounds Composed of Two Nonmetals

Drill 2.1

Please name the following compounds. Correct spelling is required.

1. MgO
2. K₂S
3. FeCl₃
4. AgI
5. CaF₂
6. Ba₃P₂
7. LiH
8. Mg₃N₂
9. SrBr₂
10. Cu₂S

Drill 2.2

Please write the correct chemical formulas.

1. calcium nitride
2. aluminum oxide
3. sodium sulfide
4. potassium hydride
5. tin(IV) bromide
6. calcium phosphide
7. potassium carbide
8. barium hydride
9. mercury(II) sulfide
10. iron(II) iodide

Link to answers to drills

III.   TERNARY SALTS

Table Listing Common Polyatomic Ions

NH4	ammonium	CN―	cyanide	OH―	hydroxide

Ternary salts are generally composed of a metal cation and an anion that consists of a group of nonmetals rather than just one.  These negatively charged anions are often called polyatomic ions.  Examples of polyatomic ions are given in Tables IV and V below.  In general, when the central atom of a polyatomic ion is bound to a higher number of oxygens, the ion name will end with “ate“.  If the central atom is bound to fewer oxygens, the ending will be “ite“.  To name ternary salts name the metal cation and then the anion.

TABLE 4: Common Polyatomic Ions

MnO4―	Permanganate	CO32―	Carbonate	PO43―	Phosphate
C2H3O2―	Acetate	SO42―	Sulfate	CrO42―	Chromate
NO3―	Nitrate	SO32―	Sulfite	Cr2O72―	Dichromate
NO2―	Nitrite	S2O32―	Thiosulfate	C2O42―	Oxalate

Table 5: Common Halogen Oxyacid Anions

ClO―	Hypochlorite	BrO―	Hypobromite	IO―	Hypoiodite
ClO2―	chlorite	BrO2―	bromite	IO2―	iodite
ClO3―	chlorate	BrO3―	bromate	IO3―	iodate
ClO4―	Perchlorate	BrO4―	Perbromate	IO4―	Periodate

 

 

Examples of ternary compounds.

1 Na		C2H3O2―	=	NaC2H3O2	Sodium acetate

The charge on the ions determines how they combine as a unit.

2 Na		CO32―	=	Na2CO3	Sodium carbonate
2(+1)		(―2)	=	0

 

Ca2		2 ClO2―	=	Ca(ClO2)­­2	Calcium chlorite
+2		2(―1)	=	0

 

2 Al3		3 SO42―	=	Al2(SO4)3	Aluminum sulfate
2(+3)		3(―2)	=	0

Parentheses are used when a polyatomic ion is factored more than once when combined to give a neutral compound.

DRILL 3

Drill 3, Table 1: Please Name the Following Compounds. Give Careful Attention to the Endings

1.	Ca3(PO4)2		2.	KNO3
3.	BaCO3		4.	LiBrO2
5.	SrSO3		6.	Mg(IO4)2
7.	Na2S2O3		8.	Cu(C2H3O2)2
9.	KMnO4		10.	K3PO4
11.	Na2CrO4		12.	Fe(BrO)3
13.	AgClO3		14.	SnSO4
15.	Na2Cr2O7		16.	CuNO2
17.	Al(ClO2)3		18.	Ca(IO)2
19.	Ba(BrO4)2		20.	Li2CO3

Drill 3, Table 2: Please Write Formulas for the Following Compounds.

1.	lithium thiosulfate		2.	tin(II) nitrate
3.	sodium carbonate		4.	ammonium sulfate
5.	strontium phosphate		6.	mercury(I) chloride
7.	copper(II) phosphate		8.	potassium dichromate
9.	magnesium chlorate		10.	lithium acetate

 

Please thoroughly master the above section before proceeding.

 

IV.BINARY ACIDS –

Water solutions of compounds composed of hydrogen and a nonmetal

 

Rule:  Acids composed of hydrogen and nonmetals are named by putting the prefix Hydro before the root of the name of the nonmetal and adding the suffix –ic acid.

 

              For example: Hydrogen chloride (HCl) dissolved in water becomes hydrochloric acid.

HF(aq)	Hydrofluoric acid
HC1(aq)	Hydrochloric acid
HBr(aq)	Hydrobromic acid
HI(aq)	Hydroiodic acid
H2S(aq)	Hydrosulfuric acid

 

 

NOTE:  The formulas of binary acids must be followed by (aq) meaning aqueous. This signifies that the binary acid is dissolved in water. The binary acids exist as gasses when not dissolved in water. For example, HBr is hydrogen bromide gas if not aqueous (aq).

 

V. Ternary Acids Containing Oxygen

Compounds of hydrogen and a polyatomic ion

 

Rules: 

1. If there is only one oxygen acid, the name is that of the characteristic element followed by the suffix ‑ic.
2. If there are two oxygen acids, the name of the one with the larger number of oxygen atoms ends in –ic acid, and the name of the one with the smaller number of oxygen atoms ends in ‑ ous acid.
3. If there are four oxygen acids, like the oxyacids of the halogen family, the acid with the greatest number of oxygens is designated by the prefix per‑ and suffix –ic acid, the one with the next fewer oxygens has the suffix –ic acid, the one with the next fewer has the suffix –ous acid and the acid with the fewest oxygens is designated with the prefix hypo and the suffix –ous acid.

Table Listing Some Common Ternary Oxyacids with Names     

HNO3	nitric acid	HNO2	nitrous acid
H2SO4	sulfuric acid	H2SO3	Sulfurous acid
HBrO4	perbromic acid	HBrO3	bromic acid
HBrO2	bromous acid	HBrO	hypobromous acid

 

     NOTE:  Ternary acid formulas are not usually followed by (aq).  It is assumed that they are dissolved in water.

 

VI.     ACID SALTS

 

When one or more hydrogens of an acid is replaced by a metal, the result is an acid salt.  We have already encountered salts which result from the replacement of all of the available hydrogens in the acid.  However, if the metal replaces only one or two of the available number of hydrogen ions from an acid, provision must be made to distinguish between the different salts that may be formed.

Table Listing Some Common Acid Salts with Names

H3PO4	Phosphoric acid
KH2PO4	potassium Dihydrogen phosphate
K2HPO4	potassium Monohydrogen phosphate
K3PO4	potassium phosphate

If the acid contains two hydrogens, then only two different salts are possible. The salts derived from these acids can be named by the method just described. However, a common method using the prefix bi is still used widely and one should be familiar with this usage as well.

Table Listing Acid Salts of Carbonic Acid and Common Bicarbonate Usage

 

H2CO3	carbonic acid
KHCO3	potassium Monohydrogen carbonate or potassium bicarbonate
K2CO3	potassium carbonate

Drill 4, Table 1: Please Name the Following Compounds. Give Careful Attention to the Endings

 

1.	H2S (aq)		2.	K2HPO4
3.	HC2H3O2		4.	HBrO
5.	H3PO4		6.	NaHCO3
7.	HIO3		8.	HBrO2

Drill 4, Table 2: Please Write Chemical Formulas for the Following Compounds.

1.	magnesium monohydrogen phosphate
2.	potassium monohydrogen sulfite
3.	perbromic acid
4.	sodium monohydrogen sulfate
5.	iodous acid
6.	chloric acid

 

Please thoroughly master the previous section before proceeding to the next.

 

VII.   DIATOMIC MOLECULES

 

        Elements existing naturally as diatomic molecules are designated by adding the word “molecular” preceding the element name.  

Table Listing the Naturally Occurring Diatomic Molecules

 

H2	molecular hydrogen	N2	molecular nitrogen
O2	molecular oxygen	F2	molecular fluorine
Cl2	molecular chlorine	Br2	molecular bromine
I2	molecular iodine

 

VIII. HYDRATES

Ionic compounds having water molecules bonded loosely within the crystal

 

Some ionic compounds exist with definite numbers of water molecules bonded loosely within the crystal.  These compounds are called hydrates and the waters are referred to as waters of hydration.  In naming a specific hydrate, first name the ionic compound then specify the number of waters with the appropriate prefix and then add the term “hydrate.” 

For example, CuSO₄ • 5H₂0 indicates five waters of hydration per copper or sulfate ion.  This compound is named copper (II) sulfate pentahydrate. An alternate system uses a number rather than a prefix & would name this compound copper (II) sulfate 5-hydrate.

IX. Practice Quiz

Practice Quiz, Table 1: Please name of each of the following.

1.	KCl
2.	Na2CO3
3.	CCl4
4.	PBr3
5.	LiNO2
6.	HBr(aq)
7.	KIO4
8.	H2SO4
9.	HBrO3
10.	NaH2PO4
11.	Na2SO4 • 2H20

 

 

Practice Quiz, Table 2: Please Write Chemical Formulas for the Following Compounds.

1.	sodium oxalate
2.	iron(II) phosphate
3.	dinitrogen monoxide
4.	potassium permanganate
5.	barium hypochorite
6.	oxalic acid
7.	molecular oxygen
8.	chloric acid
9.	ammonium sulfate
10.	magnesium cyanide
11.	iron(II) sulfate tetrahydrate