UNIT 5:
Writing and Naming Chemical Formulas
Ch. 4 in textbook
5.1 Ionic Bonding
• When it comes to bonding,
ELECTRONS call the shots!
It is the arrangement of the
valence electrons that will
dictate which kind of bond will
form.
Ionic Bonds and Ionic Compounds:
• Remember: an ION is… an atom which has lost or
gained electrons and is now CHARGED (+) or (-).
• An ionic bond:
• a cation (+) and an anion (-)… two oppositely charged ions.
The bond itself is electrically neutral (no charge associated)
so the amount of charge on the cation and the anion
MUST EQUAL!
• Anions only bond with cations… like charges will not bond
and do not want to be associated with each other.
Types of Ions:
• You have 2 distinct origins for ions:
• 1. Ions created by one atom.
• 2. Ions created by 2 or more atoms.
• Type #1 ions are called monatomic ions, which can be
subdivided into cations and anions. Remember mono is
the prefix meaning “one”.
• Type #2 ions are called polyatomic ions, poly being the
prefix meaning “many”.
POLYATOMIC IONS
• There are several polyatomic ions, both cationic and
anionic. They consist of at least 2 atoms and bond with
ions of equal charge.
Naming Ionic Compounds
• MONATOMIC CATIONS (+):
• Positive Ions
• Monatomic cations (a single atom with a non-negative charge) take
the name of the element plus the word "ion"
Examples:
• Na+ = sodium ion
• Zn 2+ = zinc ion
• Forms more than one (1) positive ion? The charge is indicated by
the Roman numeral in parentheses followed by the word "ion"
Examples:
• Fe 2+ = iron (II) ion
• Fe 3+ = iron (III) ion
* refer to the table on page 231 in your text.*
• Negative Ions
• Monatomic anions (a single atom with a negative charge)
change their ending to "-ide"
Examples:
•O
2-
= oxide
• Cl - = chloride
Binary Ionic Compounds:
• When ions bond they form ionic compounds, of which the
simplest type is the binary ionic compound.
• This occurs when only 2 elements, or 2 monatomic ions, bond. These
compounds are named by First, writing the name of the cation followed
by the name of the anion. For example… the ionic compound made of
Na and F is called sodium fluoride… the ionic compound made of Zn
and O is called zinc oxide.
• Unfortunately, these names do not tell you the ratios of the
element being bonded. Is it 1:1 or 1:3? This is
communicated by the empirical formula. This type of formula
uses the chemical symbols for the atoms of the compound,
and subscripts to indicate their RATIOS.
• When combining cations & anions into an ionic
compound, you always put the cation name first &
then the anion name (the molecules are also written in that
order as well.)
• Examples:
• Na+ + Cl - --> NaCl
sodium + chloride --> sodium chloride
+ SO4 2- -->CuSO4
copper(II) + sulfate --> copper(II) sulfate
• Cu
2+
+ NO3- --> Al(NO3)3
aluminum + nitrate --> aluminum nitrate
• Al
3+
Practice
• Compound
CaI2
Mg3P2
LiBr
Al2O3
NaCl
BN
Name
5.2 Hydrates
• When an Ionic compound absorbs H2O it is called
a HYDRATE.
• Hydrated ionic compounds have a specific
number of water molecules in their chemical
formulas.
• In the solid, these water molecules (also called "waters
of hydration") are part of the structure of the compound.
Naming Hydrates
• Rule 1. The ionic compound
(without the waters
is named first using ionic naming • 1 mono
rules.
• 2 di
• 3 tri
• Rule 2. Greek prefixes are attached to
• 4 tetra
the word "hydrate" to indicate the
• 5 penta
number of water molecules per formula
• 6 hexa
unit for the compound.
• 7 hepta
•
• 8 octa
Rule 3. When the chemical formula for a • 9 nona
hydrated ionic compound is written, the • 10 deca
formula for the ionic compound is
separated from the waters of hydration
by a "dot".
of hydration)
Practice
• CuSO4 . 5 H2O
• Copper (II) sulfate pentahydrate
• MgSO4 . 9 H2O
• Magnesium sulfate nonahydrate
• BaCl2 . 2 H2O
• barium chloride dihydrate
5.3 Covalent Bonding
• “A covalent bond is formed by a shared pair of electrons
between two atoms.”
Molecules and Their Formulas
• When atoms are bonded by a covalent bond they are called
a molecule. Theses molecules can contain 2 or more atoms
covalently bonded in any arrangement possible. To know
the elements and the ratios of those elements in the
molecule you will need to know its molecular formula. This
formula always tells us the elements, in the molecule, and
exactly how many there are being used.
• For example: The molecular formula for sucrose (table sugar) is
C12H22O11. This means we have 12 carbons, 22 hydrogens and 11
oxygens - exactly!
• Another type of formula we can use to describe the
molecule is the structural formula. This type of formula
illustrates HOW the elements are attached together, or
which atoms are bonding.
• For example: we all know H2O is water… and this is its
molecular formula. However, its structural formula is
actually HOH because each hydrogen is bonded to only
the oxygen.
Covalent Bonding Naming Rules
The more positive atom is written first (the atom
which is the furthest to the left and to the bottom of the
periodic table)
• The more negative second atom has an "-ide"
ending.
• A prefix indicates the number of each atom
present in the compound.
Covalent Prefixes
Number of Atoms
1
2
3
4
5
6
7
8
9
10
Prefix
Mono (don’t use on 1st element)
Di
Tri
Tetra
Penta
Hexa
Hepta
Octa
Nona
Deca
Practice
Formulas
CO2
CCl4
P2O5
PBr3
N2 O
Name
Carbon Dioxide
Carbon Tetrachloride
Diphosphorous Pentaoxide
Phosphorous Tribromide
Dinitrogen Monoxide
5.4 Acids
Binary acids- acids that are made of only two
elements (no Oxygen)
•
•
A. Prefix is always hydro
B. Name the second element with the suffix- ic
•
EX: HCl
Hydrochloric acid
Ternary acids- those acids that are made of more
than two elements; usually contain a polyatomic
ion (have Oxygen)
• A. For the acid containing the most common polyatomic
ion of its group simply use the first part of the
polyatomic name and follow with the suffix ic.
• B. For the acid containing the polyatomic with one less
oxygen than the ic, use the suffix ous.
• C. For the acid containing the polyatomic with two less
oxygens than the ic, use the prefix hypo and the suffix
ous.
• D. For an acid containing the polyatomic with one more
oxygen than the ic, use the prefix per and the suffix ic.
Examples of acid nomenclature
• Rule 1: all acids must contain hydrogen
• Rule 2: acids with `ic' suffix represent natural `ate'
polyatomic ions
HBrO3 bromic acid
• Rule 3: when all oxygen atoms are
removed,
add `hydro' prefix to name
HBr hydrobromic acid
HCl hydrochloric acid
• Rule 4: when an extra oxygen is added,
`per' prefix to name
HBrO4 perbromic acid
HClO4 perchloric acid
add a
• 5: when 1 oxygen is taken away (from `ate' ion
number),
change the `ic' suffix to `ous'
HBrO2
bromous acid
HClO2
chlorous acid
• Rule 6: when 2 oxygens are taken away (from
`ate' ion number), change the `ic' suffix to `ous' and
add a `hypo' prefix
HBrO
hypobromous acid
HClO
hypochlorous acid