Unit 2 Naming Conventions

NAMING COMPOUNDS: FIRST STEP

First identify the compound type: ionic, molecular (covalent), or acid. The naming rules depend on the type.

How do you recognize a binary molecular compound?

It contains two different nonmetals.

How do you recognize an ionic compound?

It usually contains a metal + nonmetal OR contains a polyatomic ion such as NH4+, NO3-, SO4^2-, etc.

How do you recognize an acid from its formula?

Acids usually begin with H and are typically written as aqueous compounds, (aq).

Binary compound

A compound containing only two different elements.

Binary molecular compound

A compound made of two different nonmetals.

Binary ionic compound

A compound made of two ions, usually a metal cation and a nonmetal anion.

NAMING BINARY MOLECULAR COMPOUNDS

Name the first nonmetal using its element name + name the second nonmetal with an -ide ending. Use prefixes to indicate the number of atoms.

First element in a molecular compound

Keep the element's normal name and use a numerical prefix when needed.

Second element in a molecular compound

Use a numerical prefix and change the element ending to -ide.

Do molecular compounds use prefixes?

Yes. Prefixes indicate the number of atoms of each element.

Do ionic compounds use prefixes such as di-, tri-, and tetra-?

NO. Numerical prefixes are not used to name ionic compounds.

Do you use mono- on the FIRST element of a molecular compound?

No. Mono- is omitted from the first element.

Can mono- be used on the SECOND element?

Yes. Example: CO = carbon monoxide.

1 atom prefix

mono-

2 atoms prefix

di-

3 atoms prefix

tri-

4 atoms prefix

tetra-

5 atoms prefix

penta-

6 atoms prefix

hexa-

7 atoms prefix

hepta-

8 atoms prefix

octa-

9 atoms prefix

nona-

10 atoms prefix

deca-

What happens when a prefix ending in a or o comes before a vowel?

The final vowel of the prefix is often dropped to make pronunciation easier.

CO name

carbon monoxide

CO2 name

carbon dioxide

N2O name

dinitrogen monoxide

N2O5 name

dinitrogen pentoxide

SO2 name

sulfur dioxide

SO3 name

sulfur trioxide

PCl3 name

phosphorus trichloride

PCl5 name

phosphorus pentachloride

P4O10 name

tetraphosphorus decoxide

NO name

nitrogen monoxide

NO2 name

nitrogen dioxide

N2O4 name

dinitrogen tetroxide

SF6 name

sulfur hexafluoride

NAMING BINARY IONIC COMPOUNDS

Name the cation first, then name the anion second with its ending changed to -ide.

Cation

Positively charged ion. Usually a metal in a binary ionic compound.

Anion

Negatively charged ion. Usually a nonmetal in a binary ionic compound.

Which ion is named first in an ionic compound?

The cation.

Which ion is named second in an ionic compound?

The anion.

How is a monatomic anion named?

Use the root of the element name + -ide.

Cl-

chloride

F-

fluoride

Br-

bromide

I-

iodide

O^2-

oxide

S^2-

sulfide

N^3-

nitride

P^3-

phosphide

H-

hydride

MgCl2 name

magnesium chloride

NaCl name

sodium chloride

CaF2 name

calcium fluoride

Al2O3 name

aluminum oxide

K2S name

potassium sulfide

Why isn't MgCl2 called magnesium dichloride?

Ionic compounds are NOT named according to the number of ions, so numerical prefixes are not used.

What must the total charge of an ionic compound equal?

Zero. Ionic compounds must be electrically neutral.

How do you write an ionic formula from ion charges?

Choose subscripts so that total positive charge + total negative charge = 0.

Mg^2+ + Cl- formula

MgCl2

Al^3+ + O^2- formula

Al2O3

Ca^2+ + N^3- formula

Ca3N2

Na+ + O^2- formula

Na2O

What is the criss-cross method?

Use the magnitude of each ion's charge as the other ion's subscript, then reduce subscripts to the lowest whole-number ratio.

Must ionic subscripts be reduced?

Yes. Ionic formulas are written in the lowest whole-number ratio.

Ca^2+ and O^2- formula

CaO, NOT Ca2O2.

FIXED-CHARGE METALS

Group 1 metals are +1, Group 2 metals are +2, Al is usually +3, Zn is +2, Ag is +1, and Cd is +2.

Group 1 metal charge

+1

Group 2 metal charge

+2

Aluminum ion

Al^3+

Zinc ion

Zn^2+

Silver ion

Ag+

Cadmium ion

Cd^2+

Do fixed-charge metals need Roman numerals?

No.

VARIABLE-CHARGE METALS

Many transition metals can form more than one charge. Their charge is specified with a Roman numeral in the compound name.

What does a Roman numeral in an ionic compound name represent?

The CHARGE of the metal cation, NOT the number of metal atoms.

Iron(II) ion

Fe^2+

Iron(III) ion

Fe^3+

Copper(I) ion

Cu+

Copper(II) ion

Cu^2+

Tin(II) ion

Sn^2+

Tin(IV) ion

Sn^4+

Lead(II) ion

Pb^2+

Lead(IV) ion

Pb^4+

FeCl2 name

iron(II) chloride

FeCl3 name

iron(III) chloride

Cu2O name

copper(I) oxide

CuO name

copper(II) oxide

How do you determine the Roman numeral from a formula?

Use the known anion charge and overall neutrality to calculate the charge on each metal ion.

How do you determine Fe charge in Fe2O3?

Three O^2- ions give -6 total. Two Fe atoms must total +6, so each Fe is +3. Name: iron(III) oxide.

Fe2O3 name

iron(III) oxide

POLYATOMIC ION

A charged group of two or more covalently bonded atoms that behaves as a single ion.

Important rule for polyatomic ions

Memorize the ion's name, formula, and charge. Keep the polyatomic ion's name unchanged when naming an ionic compound.

Ammonium

NH4+

Mercury(I)

Hg2^2+

Hydronium

H3O+

Phosphonium

PH4+