Chemistry Lecture 3C

Names and Formulas of Chemical Compounds

(Inorganic)

Formula to Name

First, you must ask yourself if the given compound is inorganic. It is an inorganic compound if it does

not contain carbon. The exceptions to this are C, CO, and CO2.

Secondly, you must determine the type of bond that is in the given compound.

Formula to Name: Ionic

If the compound contains an ionic bond, first look at the metal. Does the metal have more than one oxidation state? This can be found by looking at your

periodic table in the box labeled oxidation for the metal at which you are looking.

If no, then write the name of the metal as it appears on the periodic table. For example: Na is sodium

Formula to Name: Ionic

If the metal has more than one oxidation state, you must determine its charge in the given compound. For example: Cu2O Oxygen always has a charge of –2 in ionic

compounds, so each copper must have a charge of +1 for this compound to have an overall charge of zero.

Then write the name of the metal as it appears on the periodic table followed by its charge in Roman Numerals

Cu2O is copper (I)

Formula to Name: Ionic

Is there more than one type of non-metal in the given compound? If no, then write the name of the non-metal as given on the periodic table but change the ending of its name to –ide. Examples:

Phosphorus becomes phosphide Oxygen becomes oxide Chlorine becomes chloride

Formula to Name: Ionic

If there is more than one type of non-metal, then you have a polyatomic ion. A partial list of these can be located on

your periodic table. Examples: SO4 is sulfate, CO3 is carbonate,

OH is hydroxide, etc.

Once you find it on your periodic table, you simply write the name as given following the name of the metal.

Formula to Name: Ionic

Let’s try some out! NaCl sodium chloride

PbS2

lead (IV) sulfide

MgOH magnesium hydroxide

Formula to Name: Ionic

Questions?

Name to Formula: Ionic

Ionic compounds should be easy to recognize by their names as they should include the name of a metal followed by that of a non-metal or polyatomic ion. Examples: copper (II) sulfide sodium hydroxide calcium phosphide

Name to Formula: Ionic

First determine the symbol for and oxidation state of the metal named. Examples: sodium hydroxide: Na1+

calcium phosphide: Ca2+

copper (II) sulfide: Cu2+

Remember, if there is more than one possible oxidation state for the given metal, then look to the Roman Numeral following its name in the given formula to find its charge in the given compound.

Name to Formula: Ionic

Once you know the symbol and charge of the metal in the given compound, look at the rest of the name. If the ending of the formula name is –ide, then it is probably a single non-metal. The exception to this is hydroxide which

is a polyatomic ion.

Name to Formula: Ionic

Once you determine if it is a single non-metal you are looking for or a polyatomic ion, you must determine its symbol and charge. Examples: sodium hydroxide: OH1-

calcium phosphide: P3-

copper (II) sulfide: S2-

Name to Formula: Ionic

Now that you know the symbols for and charges of the elements involved in the given compound, you can balance the charges. The correct formula for an ionic compound is that which contains the least amount of atoms necessary to make the overall charge of the compound zero.

Name to Formula: Ionic

Let’s balance the charges for our examples! Examples: copper (II) sulfide: Cu2+ S2-

CuS the charges are equal and opposite

calcium phosphide: Ca2+ P3-

Ca3P2 3 Ca = +6, 2 P = -6 sodium hydroxide: Na1+ OH1-

NaOH the charges are equal and opposite

Name to Formula: Ionic

Let’s try some more! magnesium sulfate MgSO4

chromium (III) chloride CrCl3

manganese (II) nitride Mn3N2

Name to Formula: Ionic

Questions?

Formula to Name: Covalent

If it is an inorganic compound, but contains a covalent bond instead of an ionic bond, then the process to name it is slightly different. The main difference is that you will be using prefixes to identify the quantity of each element in the compound.

Formula to Name: Covalent

Prefix # of atoms

Prefix # of atoms

mono- 1 hexa- 6

di- 2 hepta- 7

tri- 3 octa- 8

tetra- 4 nona- 9

penta- 5 deca- 10

Formula to Name: Covalent

Determine the name of the element belonging to the leftmost symbol in the compound. Look to the right of the symbol and see if there is a small number. If there is no number, then there is only

one atom of that element. If there is a number, it denotes how

many of that element is in the compound.

Formula to Name: Covalent

Once you determine how many atoms of the element there are and the element’s name, you can write the first part of the name. If there is only one atom of the element in the compound, then you just write the name of the element.If there is more than one atom of the element in the compound, then you use the appropriate prefix followed by the element’s name.

Formula to Name: Covalent

Examples: NO

nitrogen N2O

dinitrogen SO

sulfur S2O

disulfur

Formula to Name: Covalent

For the second element in the compound, the process is almost exactly the same. The only differences are that you use a prefix even if there is only one atom of the second element in the compound and you change the ending of the name like in ionic compounds.

Formula to Name: Covalent

Let’s try some! NO nitrogen monoxide

N2O4 dinitrogen tetraoxide

SO2 sulfur dioxide

H2O dihydrogen monoxide

Formula to Name: Covalent

Questions?

Name to Formula: Covalent

Due to the use of prefixes to denote the number of atoms of each element in a covalent compound, going from name to formula is actually pretty easy. Look at the first element named. If it does not have a prefix, then there is

only one atom. If it has a prefix, then that is how many

atoms there are.

Name to Formula: Covalent

The second element in the formula name should always have a prefix to identify how many atoms there are. Simply look at the periodic table and find the non-metal which has a very similar name and the prefix will tell you how many there are.

Name to Formula: Covalent

Let’s try some! phosphorus trisulfide PS3

disulfur dioxide S2O2

silicon tetrahydride SiH4

nitrogen monoxide NO

Name to Formula: Covalent

Questions?

A Note on Naming Covalent Compounds

There is one other type of covalent compound. Some non-metals do not exist in their element form, but instead in polyatomic molecules. There is a list of these non-metals on the back of your periodic table.

A Note on Naming Covalent Compounds

Formula Name Formula Name

H2 hydrogen N2 nitrogen

Cl2 chlorine O2 oxygen

F2 fluorine Br2 bromine

I2 iodine As2 astatine

P4 phosphorus

S8 sulfur

A Note on Naming Covalent Compounds

So, if you ever see the name of a non-metal alone and it is asking for the formula, check your list of polyatomic molecules first to make sure you have the formula correct.