Chemical Bonding

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Chemical Bonding
General Chemistry

• The Ionic Model

IHG Fall 99
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The Ionic Model
Ionic compounds are made from a metal and a
nonmetal
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The Ionic Model

• The Model
• Structures and Formulas
• Naming
• Polyatomic Ions

Choose one
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The Ionic Model

• The Model
• Structures and Formulas
• Naming
• Polyatomic Ions

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The Ionic Model
The Model
An ion is an atom (or group of atoms) that has a
electrical charge as a result of the loss or gain
of electrons.
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The Ionic Model
The Model
Remember
Ions do not have equal numbers of electrons and
protons, therefore they have a charge.
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The Ionic Model
The Model
Positive ions are called cations
Negative ions are called anions
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The Ionic Model
The Model
If an atom loses electrons then it has less
negative charges than positive charges (protons),
so it has a positive charge.
Na
1e-
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The Ionic Model
The Model
Na
1e-
This equation shows the loss of 1 electron (e-)
from Na.
This free electron can be gained by another
atom.
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The Ionic Model
The Model
If an atom gains electrons then it has more
negative charges than positive charges (protons),
so it has a negative charge.
1e-
Br
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The Ionic Model
The Model
1e-
Br
This equation shows the gain of 1 electron (e-)
by Br.
Now what if we put them together?
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The Ionic Model
The Model
Na
1e-
1e-
Br
Since there is 1e- on each side of the equation
they cancel out
Leaving
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The Ionic Model
The Model
Na
1e-
1e-
Br
Na
Br


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The Ionic Model
The Model
Na
Br


The electron was exchanged between the sodium and
the bromine satisfying their need to have filled
shells.
Remember
The octet rule
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The Ionic Model
The Model
Na
Br


In fact the drive for this chemical reaction to
happen is so strong that it is a pretty violent
reaction.
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The Ionic Model
The Model
Remember
III
IV
V
VI
VII
VIII
I
II
These group numbers tell how many valence
electrons each element has
nonmetals
s
Metals
p
d
metals
metals
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The Ionic Model
The Model
III
IV
V
VI
VII
VIII
I
II
Metals tend to lose electrons to achieve an
electron configuration like the noble gases
nonmetals
s
p
d
metals
metals
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The Ionic Model
The Model
III
IV
V
VI
VII
VIII
I
II
Group IA forms 1 ions
1
nonmetals
3
s
p
Group IIA forms 2 ions
2
d
metals
metals
Group IIIA metals form 3 ions
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The Ionic Model
The Model
III
IV
V
VI
VII
VIII
I
II
Nonmetals tend to gain electrons to achieve an
electron configuration like the noble gases
nonmetals
s
p
d
metals
metals
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The Ionic Model
The Model
III
IV
V
VI
VII
VIII
I
II
Group VA forms -3 ions
nonmetals
-1
-2
-3
s
p
Group VIA forms -2 ions
d
metals
metals
Group VIIA forms -1 ions
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The Ionic Model
The Model
III
IV
V
VI
VII
VIII
I
II
Group IIIA and IVA nonmetals dont generally form
ions
nonmetals
s
p
d
Group IVA - VIIA metals behavior more like
transition metals
metals
metals
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The Ionic Model
The Model
Transition metals form positive ions and can have
more than one possible charge
III
IV
V
VI
VII
VIII
I
II
Rules for the charges on transition metals are
beyond the scope of this class. There are a few
you will have to memorize
nonmetals
s
p
d
metals
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The Ionic Model
The Model
We have looked at an atom losing one electron and
an atom gaining one electron, but what about
other charges?
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The Ionic Model
The Model
Sodium has one electron to give up.
Na
Sulfur (Group VIA) has 6 valence electrons, so it
needs two more electron to make an octet.
S
Na
We need a second Na to provide the other electron
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The Ionic Model
The Model
Na
S
Na
2

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The Ionic Model
The Model
Bromine only needs one electron to have its octet.
Br
Ca
Calcium has two electrons to give up so it can
have a noble gas configuration
Br
We need a second Br to take the other electron
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The Ionic Model
The Model
Br
Ca
Br
2

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The Ionic Model

• The Model
• Structures and Formulas
• Naming
• Polyatomic Ions

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The Ionic Model
Structures and Formulas
In ionic compounds like NaBr, there are an equal
number of Na and Br- held together by
electrostatic attraction.
Electrostatic attraction is the attraction
between the positive and negative charges of the
ions
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The Ionic Model
Structures and Formulas
The ions are arranged in patterns for that the
positive and negative charges are balanced.
When zillions of these ions are packed together
in these patterns they form crystals that have
the same pattern
See your textbook for examples of these crystals
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The Ionic Model
Structures and Formulas
Br-
Na
We can build the pattern that sodium ions and
bromide ions follow
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The Ionic Model
Structures and Formulas
There are six Na surrounding the Br-
Na
Na
Na
Br-
Na
Na
Na
One on each side, one above and one below
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The Ionic Model
Structures and Formulas
There are six Br- surrounding the Na
Br-
Br-
Br-
Na
Br-
Br-
Br-
One on each side, one above and one below
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The Ionic Model
Structures and Formulas
So we can put the two patterns together to make
one pattern.
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The Ionic Model
Structures and Formulas
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The Ionic Model
Structures and Formulas
Now we can add a few more ions
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The Ionic Model
Structures and Formulas
Na
Na
Br-
Br-
Na
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The Ionic Model
Structures and Formulas
Na
Na
1 sodium ion is behind here
Br-
Br-
Na
There are 9 sodium ions and 9 bromide ions
displayed here. Should the formula be Na9Br9?
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The Ionic Model
Structures and Formulas
For ionic compounds, we use formula units.
Formula unit refers to the smallest unit of the
ionic compound.
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The Ionic Model
Structures and Formulas
A single sodium ion is not attracted to any one
bromide ion more than any other bromide ion that
surrounds it.
But it only takes one sodium ion and one bromide
ion to have a neutral compound.
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The Ionic Model
Structures and Formulas
So the formula unit for sodium bromide is NaBr.
Br-
Na
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The Ionic Model
Structures and Formulas
Br-
Na
When we show the ions we show the charges, but
when we write the formula unit, NaBr, we do not
write the charges.
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The Ionic Model
Structures and Formulas
Br-
Br-
Ca2
It takes two bromide ions to make a neutral
compound with a calcium ion.
So the formula unit is CaBr2
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The Ionic Model
Structures and Formulas
What if I have aluminum and sulfur?
Aluminum is a metal in Group IIIA, so its charge
is 3.
Sulfur is a nonmetal in Group VIA, so its charge
is -2.
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The Ionic Model
Structures and Formulas
We can use the model to figure this out
S
Al
S
Al
S
3
2

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The Ionic Model
Structures and Formulas
There is an easier way to use the model.
3
2
So the formula unit for aluminum sulfide is Al2S3
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The Ionic Model

• The Model
• Structures and Formulas
• Naming
• Polyatomic Ions

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The Ionic Model
Naming
Binary ionic compound is an ionic compound that
has only two types of ions present.
There maybe more than two ions presents, but only
two types present.
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The Ionic Model
Naming
CaBr2 is a binary ionic compound because there
are only calcium ions and bromide ions, it
doesnt matter that there three total ions.
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The Ionic Model
Naming
Rules for naming binary ionic compounds

• The full name of the metal is given.
• The beginning of the nonmetal name is used
  followed by -ide

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The Ionic Model
Naming
NaBr is sodium bromide
Na is the metal and its name is sodium.
Br is the nonmetal and its name is bromine. We
take the first part that as the suffix, brom- and
add the -ide
NaBr - sodium bromide
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The Ionic Model
Naming
CaBr2 is calcium bromide
Ca is the metal and its name is calcium.
Br is the nonmetal and its name is bromine. We
take the first part that as the suffix, brom- and
add the -ide
CaBr2 - calcium bromide
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The Ionic Model
Naming
Notice there nothing in the name that indicates
how many calcium ions or bromide ions there are
in the compound.
This is because the charge on the calcium ion and
on the bromide ions doesnt change.
Their charges are always the same
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The Ionic Model
Naming
The charge of at least one of the ions can be
determined from the periodic table.
Remember
The group number of Group IA, IIA, IIIA metals is
the same as the charge.
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The Ionic Model
Naming
Also
Remember
Group VA nonmetals are -3 Group VIA nonmetals are
-2 Group VIIA nonmetals are -1
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The Ionic Model
Naming
What if I have aluminum and sulfur?
Aluminum is a metal in Group IIIA, so its charge
is 3.
Sulfur is a nonmetal in Group VIA, so its charge
is -2.
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The Ionic Model
Naming
The formula unit is Al2S3.
See structures and formulas for how to figure
this one out.
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The Ionic Model
Naming
The formula unit is Al2S3.
Al is the metal and its name is aluminum
S is the nonmetal and its name is sulfur. We
take the first part that as the suffix, sulf- and
add the -ide
Al2S3 - aluminum sulfide
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The Ionic Model
Naming
Remember
Transition metals can have more than one charge.
So there is an extra step to name them
A Roman numeral, in parenthesizes, after the name
of the metal indicates the charge of the metal.
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The Ionic Model
Naming
So we can name FeCl2.
Fe is a transition metal and its name is iron.
Iron can have two charges, either 2 or 3.
I know, because I have memorized it.
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The Ionic Model
Naming
So we can name FeCl2.
Iron can have two charges, either 2 or 3.
Since chloride is -1 and there is two of them, Fe
must be 2 to make a neutral compound.
FeCl2 - Iron(II) chloride
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The Ionic Model
Naming
FeCl2 - Iron(II) chloride
(II) tells me that the iron has a 2 charge and
since chloride is -1, then there must be two of
them in the formula unit.
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The Ionic Model
Naming
Of course, there are exceptions to the rule.
Although they are transition metals, silver (Ag)
and cadmium (Cd) are always 1 and zinc is always
2. Therefore no Roman numeral is used in the
naming of compounds with these metals.
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The Ionic Model
Naming
What is the formula unit of cesium oxide?
Hint
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The Ionic Model
Naming
What is the formula unit of cesium oxide?
Cesium is Cs and oxide is oxygen
Hint
CsO
Cs2O
CsO2
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The Ionic Model
Naming
What is the formula unit of cesium oxide?
Cesium is Cs and oxide is oxygen
What groups are they in on the periodic table?
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The Ionic Model
Naming
Cs is in Group IA
O is in Group VIA
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The Ionic Model
Naming
Cs is in Group IA
O is in Group VIA
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The Ionic Model
Naming
Cesium ion is a 1 and the oxide ion is -2, so
the correct formula is Cs2O
WOW!
That's Right !!
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The Ionic Model
Naming
What is the name of Cu2S?
Copper (II) sulfide
Hint
Copper (I) sulfide
Copper sulfide
Copper (II) sulfate
Copper (I) sulfate
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The Ionic Model
Naming
Copper is Cu
Sulfide is an ion of sulfur and sulfur has the
symbol S.
Where are they on the periodic table?
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The Ionic Model
Naming
What the charge on sulfur and on copper?
Sulfur is in Group VIA and copper is in Group IB
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The Ionic Model
Naming
Copper is a transition metal which can have more
than one charge so it needs a Roman numeral.
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The Ionic Model
Naming
Sulfate is a polyatomic ion, which is in the next
section.
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The Ionic Model
Naming
Sulfur is in Group VIA so has a charge of -2.
Therefore if it takes two copper ion to satisfy
the sulfur the copper has to be 1.
WOW!
That's Right !!
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The Ionic Model

• The Model
• Structures and Formulas
• Naming
• Polyatomic Ions

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The Ionic Model
Polyatomic Ions
A monoatomic ion comes from a single atom gaining
or losing electrons. Cu1 or S-2 are monoatomic
ions.
Polyatomic ions are groups of atoms, held
together by covalent bonds, that have gained or
lost electrons.
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The Ionic Model
Polyatomic Ions
Polyatomic ions are groups of atoms, held
together by covalent bonds, that have gained or
lost electrons.
Sulfate ion is example of a polyatomic ion.
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The Ionic Model
Polyatomic Ions
Sulfate ion is example of a polyatomic ion.
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The Ionic Model
Polyatomic Ions
The two extra electrons are shared among the
atoms. This will be explained in the covalent
model.
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The Ionic Model
Polyatomic Ions
Polyatomic ions dont generally lose their
identity during a chemical reaction.
Polyatomic ions can have a positive charge or
negative charge or both a positive and negative
charge.
See the table in your textbook.
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The Ionic Model
Polyatomic Ions
Polyatomic ions are not compounds by themselves
they have to have particles of the opposite
charge to make a neutral compound.
See the table in your textbook.
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The Ionic Model
Polyatomic Ions
Most common polyatomic ions have negative
charges. The only positive one of interest at
this point are NH4 and H3O.
See the table in your textbook.
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The Ionic Model
Polyatomic Ions
Hydronium, H3O, and ammonium, NH4, end in -ium
as if they were metals.
See the table in your textbook.
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The Ionic Model
Polyatomic Ions
Phosphate, PO43-, is the only common polyatomic
ion with a -3 charge.
See the table in your textbook.
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The Ionic Model
Polyatomic Ions
Cyanide,CN-, and hydroxide, OH-, are the only
common polyatomic ions that end with -ide.
See the table in your textbook.
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The Ionic Model
Polyatomic Ions
Several polyatomic ions can have different
numbers of oxygen.
Sulfate is SO42-Sulfite is SO32-
-ate goes with more oxygen
-ite goes with less oxygen
See the table in your textbook.
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The Ionic Model
Polyatomic Ions
-ate goes with more oxygen
Sulfate is SO42-Sulfite is SO32-
-ite goes with less oxygen
Both ions have the same charge.
If I memorize the -ate ions, then -ite ions are
one less oxygen.
See the table in your textbook.
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The Ionic Model
Polyatomic Ions
Although hydrogen is a nonmetal, it generally
loses an electron to become H.
The hydrogen ion, H, can be attracted to the
negative polyatomic ions.
See the table in your textbook.
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The Ionic Model
Polyatomic Ions
If the carbonate ion, CO32-, picks up one
hydrogen ion, it becomes hydrogen carbonate ion,
HCO3-.
Notice the charge of the ion has decreased by 1.
See the table in your textbook.
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The Ionic Model
Polyatomic Ions
Hydrogen carbonate ion can also be called
bicarbonate ion. The bi- refers to the hydrogen.
Sodium bicarbonate - NaHCO3 would be an example.
See the table in your textbook.
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The Ionic Model
Polyatomic Ions
If ammonium, NH4, is part of a compound, it is
named first has if it were a metal.
NH4Cl - ammonium chloride
See the table in your textbook.
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The Ionic Model
Polyatomic Ions
You need to memorize the polyatomic ions.
Put the formula on one side of a index card and
the name on the other side.
And Practice, Practice, Practice.
See the table in your textbook.
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The Ionic Model
Polyatomic Ions
When there is more than one polyatomic ion of a
given type in a compound then parenthesizes are
put around polyatomic ion and the subscript is
put outside the parenthesizes.
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The Ionic Model
Polyatomic Ions
The identity of the polyatomic ion has to be
preserved.
If the same element is in two different
polyatomic ions they are written separately.
NH4NO3 - ammonium nitrate
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The Ionic Model
Polyatomic Ions
What is the formula unit for iron(III) nitrate?
Hint
FeN3O9
FeNO2
Fe3N
Fe3NO3
Fe(NO3)3
FeN
See the table in your textbook.
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The Ionic Model
Polyatomic Ions
Fe is iron and iron is in Group VIIIB
Nitrate is a polyatomic ion, NO3-
I know because I memorized it.
See the table in your textbook.
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The Ionic Model
Polyatomic Ions
N3O93- means a polyatomic ion containing three
ntrogens and 9 oxygens.
This is NOT the same as 3 nitrate ions.
See the table in your textbook.
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The Ionic Model
Polyatomic Ions
Nitrate is NO3-
See the table in your textbook.
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The Ionic Model
Polyatomic Ions
What is the charge on the iron ion and on the
nitrate ion?
See your textbook.
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The Ionic Model
Polyatomic Ions
Fe3 and NO 3- form Fe(NO3)3
WOW!
It contains one iron ion and 3 nitrate ions.
That's Right !!