Monday
November 12, 2012
(WS - Building and
Naming Ionic
Compounds)
Monday, 11-12-12
Write the formulas for the chemical compounds that are
formed when the following atoms bond:
sodium and chlorine
NaCl
magnesium and bromine
MgBr2
calcium and oxygen
CaO
aluminum and sulfur
Al2S3
Announcements
Assignment Currently
Open
Summative or
Formative?
Date Issued
Date Due
Date Into
GradeSpeed
QUIZ 9
S6
10/26
10/26
11/16
QUIZ 10
S7
11/2
11/2
11/16
WS – Covalent
Bonding
F14
11/7
11/16
11/16
QUIZ 11
S1
11/9
11/9
11/30
Final Day
Chemical Compound
Formation and Naming
Chemical Formulas
A chemical
formula indicates
the types of atoms
and relative
number of each
type of atom in a
chemical
compound.
Chemical Formulas
For an ionic compound, the chemical
formula reveals the ratio of ions of each
element contained in the ionic matrix.
Al2O3
In the ionic compound aluminum oxide,
there are 2 ions of aluminum for every
three ions of oxygen in the ionic matrix.
Monoatomic Ions
•Ions are created when a neutral atom loses
or gains electrons in the process of
becoming stable.
•The atom no longer has equal numbers of
protons (+) and electrons (-).
•Monoatomic ions (meaning “one atom”)
are ions formed from a single atom.
•
+
H
2+
Ca
Cl
2O
Polyatomic Ions
•Polyatomic ions (meaning
“more than one atom”) are ions
formed from multiple atoms
bonded into a group.
• NH4+ Hg22+ OH- SO42• Notice that the number 1 is not shown.
Chemical Formulas
For an ionic compound made with one or more
polyatomic ions, the chemical formula still
reveals the ratio of ions, whether they are
monoatomic ions or polyatomic ions.
Al2(SO4)3
In the ionic compound aluminum sulfate,
there are 2 ions of aluminum for every
three ions of sulfate in the ionic matrix.
Cations and Anions
•When atoms lose electrons, they now
have more protons (+) than electrons
(-), and take on the + charge of the
extra protons. Positively charged
ions are called “cations.”
•When atoms gain electrons, they now
have fewer protons (+) than electrons
(-), and take on the - charge of the
extra electrons. Negatively charged
ions are called “anions.”
•K+
•NH4+
•Br•OH-
Oxidation Numbers
Oxidation numbers (the
green numbers above the
main-block groups on the
larger Periodic Table on
the right) indicate the
charge on that atom’s ion
after it has lost or gained
electrons in the process of
becoming stable.
Na+
Mg2+
Al3+
C4+/Mg2+
N3O2-
F-
Oxidation Numbers
Oxidation numbers can be used to
determine the ratio in which
atoms will bond to one another
when forming chemical
compounds.
This procedure is illustrated on
the next slide.
Crossing Oxidation Numbers
“Crossing” oxidation numbers is
a method of balancing the
charges between ions in an ionic
compound.
For example:
If an aluminum ion is bonding
with an oxygen ion:
3+
Al + O
Al2O3
2-
Notice that you
do not cross the
+ and – charge
signs, only the
numbers of the
charges.
Crossing Oxidation Numbers
It is also important to
remember that the positivelycharged cation is always listed
first in the chemical formula,
followed by the negativelycharged anion.
+
Na Cl
Therefore:
+
Never: Cl Na
Oxidation Numbers
In general, follow
this system for
determining an
elements oxidation
number:
Group 1 = 1+ (+)
Group 2 = 2+
Group 13 = 3+
Group 14 = 4+/Group 15 = 3Group 16 = 2Group 17 = 1- (-)
Group 18 = 0
Since the d-block
Transition Metals
(Groups 3-12)
have variable
oxidation states,
their oxidation
numbers will be
listed as a Roman
numeral.
Ex) Fe (III) = Fe3+
Binary Ionic Compounds
Binary ionic compounds are
compounds composed of
two different elements.
In a binary ionic compound,
the total numbers of
positive and negative
charges must be equal.
Binary Ionic Compounds
Example
Magnesium and bromine
combine to form magnesium
bromide.
2+
Mg + Br → MgBr2
It takes 2 Br- anions, each with
a 1 charge to balance Mg with
its 2+ charge!
Naming Monoatomic Ions
Monoatomic
cations are
identified
simply by
the
element’s
name.
Naming Monoatomic Ions
When
monoatomic
anions are
bonded into
compounds,
their names
are changed
to end in
–ide
Naming Polyatomic Ions
The names of
polyatomic
ions are
never
changed as
they are
bonded into
compounds.
Example
Na + NO3 æ NaNO3
sodium + nitrate æ
sodium nitrate
Polyatomic Ions
Handout:
Reference Sheet Polyatomic Ions
Worksheet
Building and Naming
Ionic Compounds