Transcript Names and Formulas for Ionic Compounds

Names and Formulas for
Ionic Compounds
Chemistry Fall 2009
Section 8.3
Formulas for Ionic
Compounds

represented by a formula providing
the simplest ratio of the ions involved
called a formula unit
– KBr = potassium bromide; 1:1 ratio

# e- gained by the nonmetallic atoms
must equal the # e- lost by the
metallic atoms; overall charge = 0
– MgCl2 = (1) Mg2+ ion & (2) Cl- ions
Determining Charge –
monatomic ions
Common Ions Based on Groups
Group Atoms that commonly Charge
form ions
on ions
1A
H, Li, Na, K, Rb, Cs
1+
2A
Be, Mg, Ca, Sr, Ba
2+
3B
Sc, Y, La
3+
5A
N, P, As
36A
O, S, Se, Te
27A
F, Cl, Br, I
1-
Oxidation Numbers and Writing
Ionic Compound Formulas
Oxidation number – the oxidation number or
oxidation state of an element in an ionic compound
equals the number of electrons transferred from an
atom of the element to form the ion.
 The oxidation numbers are used to determine the
formulas for the ionic compounds they form.
 Oppositely charged ions combine chemically in
definite ratios to form a compound that has no
charge.
 If you add the oxidation number of each ion
multiplied by the number of these ions in a formula
unit, the total must be 0.
– Example: K has a charge of +1 and O has a charge of -2.
If the charges are not the same, subscripts must be
determined to indicate the ratio of (+) to (-) ions. K2O
– H/O Counting Atoms Worksheet
Charge of Transition Metals



P. 222 in textbook: Common Ions of
Transition Metals
Charge of a monatomic ion = oxidation
number
The number of e- transferred from an atom
of the element to form the ion
– Na+ and Cl– Positively charged ion of a metal and negatively
charged monatomic ion of a nonmetal
– Oxidation state of Na is +1; Cl is 1– Transition metals can form several different
positive ions based on the variance in ionic
charges of atoms in the groups
Now you try…
Write the correct formula for the ionic
compound composed of the following pairs
of ions:
a. potassium and iodide
b. magnesium and chloride
c. aluminum and bromide
d. cesium and nitride
e. barium and sulfide
H/O Writing Formulas Practice

Polyatomic Ions

Polyatomic ions = ions made up of
more than one atom
– Charge given applies to the entire group of
atoms
– Exists as a unit, never change subscripts of
the atoms within the ion
– If more than one is needed, place
parentheses around the ion and write the
appropriate subscript outside the
parentheses Mg(ClO3)2
Polyatomic Ions you
should memorize…
ammonium (NH4)
nitrite (NO2-)
nitrate (NO3-)
hydroxide (OH-)
chlorite (ClO2-)
sulfite (SO32-)
sulfate (SO42-)
phosphate (PO43-)
carbonate (CO32-)
chlorate (ClO3-)
Now you try…
Determine the correct formula for the
ionic compound composed of the
following pairs of ions:
a. sodium and nitrate
b. calcium and chlorate
c. aluminum and carbonate
d. potassium and chromate
e. magnesium and carbonate

Naming Ions and Ionic
Compounds

1.
2.
•
Oxyanion = polyatomic ion composed of
an element bonded to one or more oxygen
atoms
The ion with more oxygen atoms is named
using the root of the nonmetal plus the
suffix –ate.
The ion with fewer oxygen atoms is
named using the root of the nonmetal plus
the suffix –ite.
Ex. NO3-
nitrate
NO 2-
nitrite
SO42-
sulfate
SO32-
sulfite
Oxyanions forming with
halogens
1.
2.
3.
The oxyanion with the greatest number of
oxygen atoms is named using the prefix
per-, the root of the nonmetal, and the
suffix –ate
The oxyanion with one less oxygen atom
is named with the root of the nonmetal
and the suffix –ate
The oxyanion with two fewer oxygen
atoms is named using the root of the
nonmetal plus the suffix -ite
Oxyanions forming with
halogens cont.
4. The oxyanion with three fewer
oxygen atoms is named using the
prefix hypo-, the root of the nonmetal,
and the suffix –ite
ClO4ClO3ClO2ClOperchlorate
chlorate
chlorite
hypochlorite
Naming Ionic Compounds
1.
2.
3.
Name the cation first and the anion
second – CsBr
Monatomic cations use the element
name – Cs is Cesium
Monatomic anions take their name
from the root of the element name
plus the suffix –ide – CsBr (bromide)
Naming Ionic Compounds
Cont…
4. Group 1A and group 2A metals have only
one oxidation number. Transition metals
and metals on the right side of the periodic
table often have more than one oxidation
number – Fe2O3 is named iron (III) oxide
5. If the compound contains a polyatomic ion,
simply name the ion.
NaOH is sodium hydroxide
Now you try…
Name the following compounds:
a. NaBr
b. CaCl2
c. KOH
d. Cu(NO3)2
e. Ag2CrO4
H/O Naming Ionic Compounds
Complete the following
table…
Oxide
Potassium
Barium
Aluminum
Ammonium
Chloride
Sulfate
Phosphate