Unit 6:
Writing and
Naming Chemical
Formulas
CHEMISTRY I
2013-2014
Ions &
The Octet Rule
Vocabulary

Ion – an atom or bonded group of atoms with a
positive or negative charge

Anion – a negatively charged ion

Cation – a positively charged ion

Octet Rule – “atoms lose, gain, or share electrons in
order to acquire the stable electron configuration of
a noble gas”
Ion

An ion is an atom or group of atoms that has either
a positive or negative charge
Atoms form ions by gaining or
losing electrons

Atoms gain or lose electrons to
become stable

An atom is stable when the
valence shell is full
Cations – Positive Ions

Sodium loses one electron to become stable

Results in an ion that has a positive charge
Cations

The symbol “+” is written as a superscript to indicate
that the sodium has a charge of 1+
Na+
Anions – Negative Ions

Chlorine gains one electron to become stable

Results in an ion with a negative charge
Anion

The symbol “-” is written as a superscript to indicate
that the chlorine ion has a charge of 1-
Cl-
The Octet Rule

Both ions have a full valence shell containing the maximum
number of electrons possible (8)

This new arrangement of valence electrons has less energy than
the previous arrangement and is stable
Na+
Cl-
Noble Gases

A metal atom that has lost electrons (cation) and a
nonmetal atom that has gained electrons (anion)
will have the same number of electrons as its
nearest noble gas.
Common Charges
Naming Ions

Cations: A metal that has lost electrons to become an ion
has the same name as the element

Ca2+ = calcium ion

Anions: A nonmetal that has gained electrons to become
an ion has the same name as the element but with the
ending changed to –ide

S2- = sulfide ion

Nitrogen  Nitride
Phosphorous  Phosphide

Oxygen  Oxide
Flourine  Flouride
Roman Numerals for Multivents

Multivents – an element that can form an ion in more than one
way

Naming: Always include the ion charge as Roman numerals in
brackets

Cu+
copper (I)
“copper one”

Cu2+
copper (II)
“copper two”
Transition Metals to Know

Scandium column: always +3, no Roman numeral
needed

F-block: always +3, no Roman numeral needed

Ag: always +1, no Roman numeral needed

Cd & Zn: always +2, no Roman numeral needed

Sn & Pb: either +2 or +4
Charges  Oxidation Number

An oxidation number is the positive or negative
charge of an ion
Element
Oxidation #

Li
+1

Be
+2

O
-2

F
-1
Polyatomic
Ions
Writing and
Naming Ionic
Compounds
Ionic Compounds

Cation + anion

Name the cation first (typically a metal) just as it
appears on the periodic table

Na+ = Sodium

Ca+2 = Calcium
Ionic Compounds

Write the anion next (typically a nonmetal)

Change the ending to –ide

**If the anion is a polyatomic ion, the name stays
the same**
Practice

NaCl
Sodium Chloride

AlCl3
Aluminum Chloride

Na2O
Sodium Oxide

Al2O3
Aluminum Oxide
How to determine the
Oxidation Number of Transition
Metals

Identify the metal as a Transition
with multiple oxidation numbers
(ex. Fe)

Uncross the “criss-cross”

If nothing to uncross, identify the
charge of the anion. The
charges have been simplified

Transition metals will be the
same just +
+3
-2
Fe2O3
Iron (III) Oxide
+2
FeS
-2
Iron (II) Sulfide
Practice

CuO

Name: Copper (II) Oxide
Writing Ionic Formula

Identify the ions and
their charges

Criss-Cross the
charges

The sum of the
oxidation numbers
must equal zero, so by
writing the subscripts
we are able to
balance the charge

Example: Calcium
Chloride

Ions: Ca+2 and Cl-1
+2
-1
Ca
Cl

Formula = CaCl2

(Don’t write 1’s)
Practice

Magnesium Oxide

Mg2O2
**Simplify to MgO

Copper (I) Phosphide

Cu3P
Polyatomic Ions

You can’t change the subscripts in Polyatomic Ions

Put the Polyatomic Ion in brackets and place the
subscripts outside those
Calcium Phosphate
Ca+2
PO43-
Ca3(PO4)2
Naming
Covalent
Compounds
What’s the difference
between covalent and ionic?

Ionic compounds have a metal and a nonmetal, a
cation and an anion

Covalent compounds are called molecules

They are made from elements that are similar in
electronegativity
Covalent Naming uses Prefixes
1. Mono
6. Hexa
2. Di
7. Hepta
3. Tri
8. Octa
4. Tetra
9. Nona
5. Penta
10.deca
Rules



If you have more than one
atom of that element in the
compound, you will need a
prefix before it’s name.

P2O5

Diphosphorous pentoxide
Always put a prefix before the
name of the second element

CO

Carbon monoxide
Change the ending of the
second element to -ide
Practice
 OF2
 Oxygen
diflouride
 SO2
 Sulfur
dioxide
 SO3
 Sulfur
trioxide
 N2O5
 Dinitrogen
pentoxide
 N2O4
 Dinitrogen
tetroxide
 H2O
 Dihydrogen
monoxide
http://www.lhup.edu/~dsimanek/dhmo.htm
Names and
Formulas of
Common
Acids and
Bases
Naming Acids

Acids are almost always compounds made from
hydrogen and an anion

Hydrogen + Halogen = hydro________ic acid


Hydrogen + Polyatomic ion –ate = _______ic acid


HCl = hydrochloric acid
HNO3 = nitric acid
Hydrogen + Polyatomic ion –ite = _______ous acid

H2SO3= sulfurous acid
Naming Bases

Bases are almost always compounds made
from hydroxide (HO-) and a cation

Cation + Hydroxide

Mg(OH)2 = Magnesium Hydroxide

LiOH
= Lithium Hydroxide
Practice

Hydroiodic acid

HI

HBr

Hydrobromic Acid

H2CO3

Carbonic Acid

Lead (II) Hydroxide
Pb(OH)2

Sn(OH)4

Stannic Hydroxide

Zn(OH)2


Zinc Hydroxide
Empirical and
Molecular
Formulas
Empirical Formula

The formula that gives the simplest whole
number ration of atoms in a compound

Molecular Formula:
C6H12O6

Empirical Formula:
CH2O
What is the empirical formula
of…?
 C6H12O6
 CH2O
 Fe3O2
 Fe3O2
 C6H10O4
 C3H5O2