FC 1.5 PA 35 and 36 Teacher Version
FC 1.5 PA 35 and 36 Teacher Version
FC 1.5 PA 35 and 36 Teacher Version
Background
When
ions
come
together
to
form
ionic
compounds,
the
positively
charged
cations
and
negatively
charged
anions
are
attracted
in
a
ratio
determined
by
the
charges
on
the
ions.
As
an
example
we
will
discuss
sodium
oxide.
A
sodium
ion
has
a
charge
of
positive
one
(1+),
while
an
oxygen
ion
has
a
charge
of
negative
two
(2-‐).
Each
oxygen
ion
will
attract
an
average
of
two
sodium
ions
because
its
charge
is
twice
that
of
sodium.
Therefore
we
write
the
chemical
formula
for
sodium
oxide
as
Na2O,
indicating
that
for
every
two
sodium
ions
there
is
one
oxide
ion.
In
this
activity
you
will
explore
this
concept
more
fully.
Note
that
a
polyatomic
ion
is
simply
a
group
of
atoms
attached
together
that
has
an
overall
charge,
meaning
that
if
you
counted
all
of
the
protons
and
all
of
the
electrons
within
the
atoms
of
the
polyatomic
ion,
there
would
be
an
unequal
number
of
protons
and
electrons,
and
therefore
an
overall
charge.
In
ionic
bonding,
you
can
think
of
a
polyatomic
ion
as
similar
to
a
monatomic
(single
atom)
ion
in
the
way
it
behaves.
This
means
that
in
this
activity
you
can
treat
a
sulfate
ion
(SO42-‐)
the
same
way
you
treat
an
oxide
ion
(O2-‐).
It
is
important
to
understand
that
while
the
positive
and
negative
charges
in
an
ionic
compound
balance
each
other
out
on
a
macroscopic
level,
the
charges
themselves
still
exist.
This
means
that
when
you
dissolve
NaCl
in
water,
even
though
the
sodium
chloride
crystals
are
neutral
overall,
the
individual
sodium
ions
are
still
positively
charged
and
the
individual
chloride
ions
are
still
negatively
charged.
Materials:
Student
handout
Scissors
Directions
for
Activity
II:
You
will
use
cutout
representations
of
positively
and
negatively
charged
ions
to
learn
how
ions
come
together
to
form
neutral
ionic
compounds,
or
salts.
1. Cut
out
all
of
the
ions
provided.
Using
these
cutouts,
combine
positive
and
negative
ions
to
make
the
compounds
listed
in
the
table
below,
obeying
the
simple
rule
that
you
can
leave
no
“arrows”
on
the
positive
ions
without
a
“hole”
on
the
negative
ions,
and
no
“holes”
without
an
“arrow”.
Prescriptive
Activities:
Facet
Cluster
1.5:
PF#35
and
36
Teacher
Page
“arrows”
Mg
2+ “holes”
Cl
-‐
Note:
If
you
do
not
know
the
names
or
symbols
of
the
polyatomic
ions
or
elements,
refer
to
the
tables
in
your
textbook.
Compound
How
many
How
many
What
is
the
What
is
the
positive
ions
negative
ions
ratio
of
positive
chemical
were
used?
were
used?
to
negative
formula
of
the
ions?
compound?
Magnesium
fluoride
1
2
1:2
MgF2
Calcium
oxide
Sodium
chloride
Sodium
sulfide
Sodium
phosphate
Ammonium
chloride
Ammonium
phosphate
Aluminum
oxide
Aluminum
phosphate
2. Now
see
if
you
can
come
up
with
some
other
compounds
using
the
ions
provided.
Write
the
names
and
chemical
formulas
for
these
compounds.
Name
Chemical
Formula
Prescriptive
Activities:
Facet
Cluster
1.5:
PF#35
and
36
Teacher
Page
It
is
important
to
recognize
that
these
cutout
ions
are
simply
a
representation,
or
model,
used
to
illustrate
the
concept
of
formulas
for
ionic
compounds.
As
with
all
models,
there
are
constraints
on
how
well
this
represents
reality.
Discussion
Questions
1. How
is
this
model
helpful
in
understanding
chemical
formulas
for
ionic
compounds?
2. What
are
some
limitations
of
this
model
in
accurately
representing
ionic
compounds?
3. How
can
this
model
be
improved
to
better
illustrate
the
concept
of
chemical
formulas
for
ionic
compounds?
While
you
have
just
looked
at
a
model
for
determining
the
ratio
of
ions
within
an
ionic
compound,
a
difficult
concept
to
understand
is
that
within
an
ionic
crystal
each
ion
is
surrounded
by
oppositely
charged
ions
creating
an
extensive
lattice
of
connected
ions.
The
activity
you
just
did
allows
you
to
figure
out
the
ratio
of
these
oppositely
charged
ions
yet
it
is
important
to
understand
the
actual
3-‐dimensional
nature
of
how
these
ions
interact
in
a
solid
crystal.
Several
examples
of
ionic
compounds
are
illustrated
below.
NaCl
(1:1
ratio
of
ions)
CaF2
(1:2
ratio
of
ions)
Fe2O3
(2:3
ratio
of
ions)
http://www.human-‐ http://commons.wikimedia.org/wiki http://en.wikipedia.org/wiki/Iron
existence.com/blog/?page_id=262/
/File:Calcium-‐fluoride-‐3D-‐ionic.png
%28III%29_oxide
Prescriptive
Activities:
Facet
Cluster
1.5:
PF#35
and
36
Teacher
Page
Na+
CO32-‐
Al3+
Na+
NH4+
Na+
CO32-‐
K+
K+
NH4+
K+
CO32-‐
NH4+
Prescriptive
Activities:
Facet
Cluster
1.5:
PF#35
and
36
Teacher
Page
H+
SO42-‐
Al3+
H+
NH4+
H+
SO42-‐
K+
K+
NH4+
K+
SO42-‐
NH4+
Prescriptive
Activities:
Facet
Cluster
1.5:
PF#35
and
36
Teacher
Page
Ca2+
S2-‐
S2-‐
Mg2+
O2-‐
O2-‐
K+ F-‐ Cl-‐
K+
F-‐
F-‐
Prescriptive
Activities:
Facet
Cluster
1.5:
PF#35
and
36
Teacher
Page
TEACHER
NOTES:
This
activity
can
be
done
individually
at
home
or
in
small
groups
in
class.
Answer
Key
Compound
How
many
How
many
What
is
the
What
is
the
positive
ions
negative
ions
ratio
of
positive
chemical
were
used?
were
used?
to
negative
formula
of
the
ions?
compound?
Magnesium
fluoride
1
2
1:2
MgF2
Calcium
oxide
1
1
1:1
CaO
Sodium
chloride
1
1
1:1
NaCl
Sodium
sulfide
2
1
2:1
Na2S
Sodium
phosphate
3
1
3:1
Na3PO4
Ammonium
chloride
1
1
1:1
NH4Cl
Ammonium
3
1
3:1
(NH4)3PO4
phosphate
Aluminum
oxide
2
3
2:3
Al2O3
Aluminum
phosphate
1
1
1:1
AlPO4