4.2: NAMES AND FORMULAS OF
COMPOUNDS
Pages 184-201
NAMES AND FORMULAS OF IONIC COMPOUNDS
Ionic Compounds: can be represented by:
name and/or chemical formula
1. Name:
- always a metal (+ ion) followed by non-metal
(- ion)
- the non-metal ion always ends in the suffix “ide”:
Eg: aluminum fluoride
2. Chemical Formula: subscripts indicate the ratio of
(+) to (-) ions present in a compound.
Eg: AlF3
YOUR TURN!!!
Name the following ionic compounds:
#1. Li2N
Answer: lithium nitride
#2. GaI3
Answer: gallium iodide
#3. Fe2O3
Answer: iron oxide
#4. In what ratio do the atoms
of each compound combine?
WRITING FORMULAS OF BINARY IONIC
COMPOUNDS
 Ionic compounds containing only 2 elements:
positive charges balance the negative charges
Example: aluminum fluoride
Step #1: Identify each ion and its charge:
Al3+
FStep #2: determine total charges needed to balance
positive and negative.
*Charge is balanced
Al 3+:
= +3
when the overall
charge equals 0.
F 1- : -1 -1 -1 = - 3
CONT’D
Step #3: Note the ratio of positive ions to
negative ions:
1 Al3+ ion
3 F- ions
Step 4: Use subscripts to write the formula:
AlF3
*Subscripts must be written in lowest
terms.
COMPOUNDS CONTAINING A MULTIVALENT METAL
 Recall:
Multivalent metals can form 2 or more
different positive ions.
 The
periodic table lists the most common ion
charge first.
Examples: Look at your periodic table.
A)
B)
What are the charges of Nickel, Copper &
Manganese?
Which charge is each element most likely found
within a compound?
NAMING A MULTIVALENT METAL
 In
order to distinguish between multivalent
metals, each ion needs its own specific name.
 Roman
numerals are used to indicate an ions
charge.
I
– VII are used to show ion charges 1+ to 7+
 I, II, III, IV, V, VI, VII
HOW TO SHOW THE CHARGE WHEN NAMING A
MULTIVALENT METAL
For example look at Ni:
Ni can form two different ions: Ni2+ or Ni3+
Therefore in an ionic compound Ni can be
written as:
nickel (II)
or
nickel (III)
When read aloud, they read as follows:
nickel two
and
nickel three
WHAT ROMAN NUMERALS REVEAL ABOUT AN
ION OF A METAL
1. Indicates that there is more than one ion for
that metal (multivalent).
2. Tells you the exact charge of the metal ion.
(See page 189 for examples)
HOW TO WRITE THE CHEMICAL FORMULA
CONTAINING MULTIVALENT ATOM
Write the formula for the compound: Chromium (III )bromide:
Step 1 - Identify each ion and its charge:
chromium (III): Cr3+
Bromide: Br –
Step 2 - Determine the total charges needed to balance the
charge:
Cr3+:
= +3
Br - : -1 -1 -1 = - 3
Step 3 - Note ratio of positive to negative ions:
1 Cr3+ ion for every
3 Br – ions
Step 4 – Use subscripts to write formula (a “1” is never
shown):
CrBr3
NAMING A MULTIVALENT COMPOUND
What is the name of the following compound?
Au3N
Step 1 – Identify the Metal: gold (Au)
Step 2 – Check the periodic table to see if it is
multivalent:
YES: Au3+ and Au +
Step 3 – Determine the ratio of the ions in the
formula:
Au3N = 3 gold ions for every 1 nitride ion.
Step 4 – Note the charge of the negative ion
using the periodic table:
N has a charge of 3-
CONT’D
Step #5 – (+) and (-) charges must balance.
Determine the charge on the metal ion that
balances the negative ion:
Since we know N has a charge of 3- the Au
ion must have a charge of 1+ for it to balance
the one N ion with a charge of 3Thus the name of the gold ion must be gold(I).
Step #6 - Write the name of the compound:
gold (I) nitride
POLYATOMIC IONS
 An
ion composed of more than one type of
atom joined by covalent bonds.
 Carry
an electric charge.
 The
suffix “ite” and “ate” are used to indicate
the presence and number of oxygen atoms.
 Rule
“ate” polyatomic ions have one more
oxygen than “ite” polyatomic ions.
 Eg: PO43- : phosphate vs PO33-: phosphite
WRITING THE FORMULA FOR A POLYATOMIC ION
Write the formula for the following polyatomic ion:
manganese (III) chlorate
Step #1- identify each ion and its charge:
manganese (III): Mn3+
chlorate: ClO3- (refer to Table 4.11, pg 192)
Step #2-Balance charges:
Mn3+ :
= +3
ClO3- : -1 -1 -1 = - 3
Step #3 – Note ratio of positive to negative ions:
1 Mn3+ :
= +3
3 ClO3- : -1 -1 -1 = - 3
CONT’D
Step #4 – Use brackets around ions to show
ratio of ions:
(Mn)(ClO3)3
Step #5 – Omit brackets if the value outside
the brackets is 1:
Mn(ClO3)3
NAMING COVALENT COMPOUNDS
Lets review what we know:
Ionic Compounds
 In ionic compounds subscripts are not used
to indicate the actual ratio of ions within a
molecule but the smallest whole number
ratio.
Covalent Compounds
 In covalent compounds subscripts are used
to show the precise actual number of atoms
of each element in the molecule.
NAMING BINARY COVALENT COMPOUNDS
 Binary
Covalent Compound: contains 2 nonmetals joined together by one or more
covalent bonds.
Recall: atoms in covalent bonds do not
bond by forming ions but rather share
electrons.
 Binary
Covalent compounds can be made up
of many atoms: C25H52 or can by diatomic:
O2
NAMING COVALENT BONDS
Prefixes and their Meanings:
 Indicates the number of atoms present in each
element.
 Prefixes
are ONLY used for binary covalent
compounds.
 We
will first begin by studying prefixes for
naming compounds that do not contain H:
- See Table 4.13 on pg. 194
FOR BINARY COMPOUNDS NOT CONTAINING H
RULES:
#1. Prefix for the 1st element (+ ion) is only shown if it is
present more than once: eg. CCl4
#2. Prefix “mono-” is shortened to “mon-” if placed
before an oxide (- ion).
STEPS TO WRITING BINARY COVALENT COMPOUND
NAMES
Eg - Write the name of: N2O3
Step #1- Name the element on the left first:
nitrogen
Step #2 – Name the 2nd element:
Oxygen becomes oxide (recall the “ide” ending)
Step #3 – Add a prefix to each element:
dinitrogen trioxide
NAMES AND FORMULAS OF COVALENT COMPOUNDS
Covalent Compounds: both the name and
chemical formula indicates the # or quantity of
each type of atom.
For Example:
dinitrogen trioxide
OR
N2O3
carbon disulfide
OR
CS2
REVIEW RULES FOR NAMING FORMULAS

Page 196