Technical Science
Introduction to Chemistry
Chemical Formulas
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In this tutorial you will…
–
Analyze a Chemical Formula
–
Determine Formulas for Simple Salts
–
Name Salts with Multivalent Metals
–
Examine Salts with Polyatomic Ions
–
Examine Chemical Formulas for Acids
–
Examine Chemical Formulas for Bases
Analyze a
Chemical Formula
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The type of element is expressed by the chemical
symbol of the element.
●
You know that the compound NaCl is composed of
Sodium and Chlorine because the chemical
formula includes both of their symbols.
●
A Chemical Formula tells which elements make up
a compound and how many atoms of each element
are needed to make a single molecule.
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Home
NaCl
Symbol for Sodium
Analyze a
Chemical Formula
2 of 8
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The more metallic element is written first in a
chemical formula.
NaCl
Sodium Metal
Chlorine Nonmetal
MgO
Magnesium Metal
Oxygen Nonmetal
CO
Carbon Nonmetal
Oxygen Nonmetal
Although Carbon is a nonmetal,
Analyze a
Chemical Formula
3 of 8
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The subscript tells you the number of atoms that are
bonded together to make one molecule.
MgCl
2
Subscript
The subscript 2 tells us that there are two Chlorine ions involved in bonds to make a
molecule of Magnesium Chloride. There is no subscript on the Magnesium
ion. This is because there is only one Magnesium ion in this molecule. Subscripts of 1 are not written out. This formula tells us that one molecule of
Analyze a
Chemical Formula
●
What do the following chemical formulas tell you?
4 of 8
NaCl
Li
2
S
Fe
2
O
3
= 1 Sodium bonded to 1 Chlorine
= 2 Lithiums bonded to 1 Sulfur
Analyze a
Chemical Formula
5 of 8
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Subscripts are extremely important in a chemical
formula because they determine the compound.
CO
2
A molecule with 1 Carbon bonded to 2 Oxygens.CO2 is the formula for Carbon Dioxide. Carbon Dioxide is the gas you exhale all day long.CO
A molecule with 1 Carbon bonded to 1 Oxygen.CO is the formula for Carbon Monoxide.Carbon Monoxide is a deadly gas in your car’s exhaust.
When you change the subscript, you change the number of atoms involved in bonds to make the molecule and therefore you change the compound.
Analyze a
Chemical Formula
6 of 8
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There is another number that you may see written
in front of a chemical formula.
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This number is called the Coefficient.
●
The Coefficient is used to tell how many molecules
of the compound are present.
3MgCl
2
Coefficient
This tells us there are three molecules of Magnesium Chloride (MgCl2).
Each molecule has
Analyze a
Chemical Formula
7 of 8
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Coefficients only tell the number of molecules
of a compound.
CO
2
2CO
2
3CO
2
= 1 molecule of Carbon Dioxide
= 2 molecules of Carbon Dioxide
= 3 molecules of Carbon Dioxide
Changing the Coefficient doesn’t change the compound. All the formulas above are carbon dioxide.
Analyze a
Chemical Formula
8 of 8
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Interpret the following chemical formulas.
CaCl
2
2N
2
3Al
2
S
3
=
1 molecule of Calcium Chloride (CaCl
2)
The molecule has 1 Calcium bonded
to 2 Chlorines.
=
2 molecules of Nitrogen Gas (N
2)
Each molecule has 2 Nitrogen atoms
bonded to each other.
=
3 molecules of Aluminum Sulfide (Al
2S
3)
Each molecule has 2 Aluminum atoms
bonded to 3 Sulfurs.
Determine Formulas
for Simple Salts
1 of 12
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You know what the subscript in a chemical
formula means but how do you know what those
subscripts should be?
Home
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Why is sodium chloride always NaCl (one sodium
bonded to one chlorine)? Why is water always
H
2O (2 hydrogens bonded to one oxygen)?
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Again, we need to go back to “what atoms want”.
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Atoms gain or lose electrons to fill the S & P
orbitals of their outer level.
Determine Formulas
for Simple Salts
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In order to determine chemical formulas, we need
to have some compounds with which to work.
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We are going to concentrate on compounds that are
composed of metals bonded to nonmetals.
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These compounds are classified as Salts.
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When you think of salt, you probably think of
Sodium Chloride (table salt). But this is just one
member of very large group of compounds.
Determine Formulas
for Simple Salts
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Let’s start with the atoms from the Groups that
tend to do the same thing every time.
1 H 1.0 2 He 4.0 3 Li 7.0 4 Be 9.0 5 B 11.0 6 C 12.0 7 N 14.0 8 O 16.0 9 F 19.0 10 Ne 20.0 11 Na 23.0 12 Mg 24.5 13 Al 27.0 14 Si 28.0 15 P 31.0 16 S 32.0 17 Cl 35.5 18 Ar 40.0 19 K 39.0 20 Ca 40.0 21 Sc 45.0 22 Ti 48.0 23 V 51.0 24 Cr 52.0 25 Mn 55.0 26 Fe 56.0 27 Co 59.0 28 Ni 58.5 29 Cu 63.5 30 Zn 65.5 31 Ga 69.5 32 Ge 72.5 33 As 75.0 34 Se 79.0 35 Br 80.0 36 Kr 84.0 Group 1
2 3 4 5 6 7
8
Group e- in outer
S&P orbitals Reaction Resulting Ions 1 2 6 7 8 +1
+2 -2 -1
1 Lose 1 e- +1
2 Lose 2 e- +2
6 Gain 2 e- -2
7 Gain 1 e- -1
8 No
Reaction
Determine Formulas
for Simple Salts
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Remember, atoms can’t take electrons unless they
can find someone to give. Atoms can’t give
electrons unless they can find someone to take.
Na
Sodium, from Group 1, has 1 electron in its outer energy level.
Chlorine, from Group 7, has 7 electrons in its outer energy level.
Cl
Sodium wants to give one electron.
Chlorine wants to take one electron.
Since sodium wants to give one electron and chlorine wants to take one electron, a molecule of Sodium Chloride is made up of
one sodium bonded to one chlorine.
Na Cl
We can get the same information by looking at the charges the atoms take on after they
react. These charges are sometimes called the valence or the oxidation number and they result from a gain or loss of electrons.
Sodium in Group 1 takes on a +1 charge.
Chlorine in Group 7 takes on a –1 charge.
+1 -1
A molecule, by definition, must have an overall charge of Zero.
This means all the positive charges must equal all the negative charges.
(electrons lost = electrons gained)
One sodium atom with a +1 charge balances out one chlorine atom with a –1 charge. So, a molecule of sodium chloride has one sodium atom bonded to one chlorine atom
Determine Formulas
for Simple Salts
5 of 12
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Write the chemical formula for Magnesium Oxide.
The name of the molecule is Magnesium Oxide.
So we know there must be at least one Magnesium atom and
at least one Oxygen atom.
Mg O
Magnesium in Group 2 takes on a +2 charge.
Oxygen in Group 6 takes on a –2 charge.
+2 -2
One magnesium with a +2 charge balances out one oxygen with a –2 charge.
So, a molecule of Magnesium Oxide has one magnesium atom bonded
to one oxygen atom
The formula for Magnesium Oxide is MgO. One Magnesium balances out one Oxygen
for an overall charge of zero.
Notice: the charges on the atoms are not included in the chemical formula.
Determine Formulas
for Simple Salts
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Write the chemical formula for Lithium Sulfide.
The name of the molecule is Lithium Sulfide.
So we know there must be at least one Lithium atom and
at least one Sulfur atom.
Li S
Lithium in Group 1 takes on a +1 charge. (Lithium wants to give 1e-)
Sulfur in Group 6 takes on a –2 charge. (Sulfur wants to get 2 e-)
Will one lithium react with one sulfur?
+1 -2
One Sulfur has a -2 charge but one Lithium has only a +1 charge. So…
To make a molecule with an overall charge of zero we need another positive charge. That means we need another lithium atom.
The formula for Lithium Sulfide is Li2S. It takes two Lithiums to balance out one Sulfur for an overall charge of zero. Notice: the charges on the atoms are not
included in the chemical formula.
Determine Formulas
for Simple Salts
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Write the chemical formula for Calcium Chloride.
The name of the molecule is Calcium Chloride.
So we know there must be at least one Calcium atom and
at least one Chlorine atom.
Ca Cl
Calcium in Group 2 takes on a +2 charge. (Calcium wants to give 2e-)
Chlorine in Group 7 takes on a –1 charge. (Chlorine want to get 1 e-)
Will one Calcium react with one Chlorine?
+2 -1
One Calcium has a +2 charge but one Chlorine has only a -1 charge. So…
To make a molecule with an overall charge of zero we need another negative charge. That means we need another chlorine atom. The formula for Calcium Chloride is CaCl2.
It takes two Chlorines to balance out one Calcium for an overall charge of zero.
Notice: the charges on the atoms are not included in the chemical formula.
CaCl
2
Determine Formulas
for Simple Salts
8 of 12
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Write the chemical formulas for the following salts
then click for the answers.
Name
Formula
Name
Formula
Sodium
Bromide
Potassium
Sulfide
Beryllium
Oxide
Calcium
Bromide
Lithium
Oxide
Cesium
Oxide
Barium
Fluoride
Strontium
Chloride
NaBr
BeO
Li
2O
BaF
2K
2S
CaBr
2Cs
2O
9 of 12
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You have written chemical formulas when given the
name of the compound .
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Next you will name compounds given the chemical
formula
●
Once again, we will be concentrating on salts that
are composed of metal atoms from Groups 1 & 2
bonded to nonmetal atoms from Groups 6 & 7
●
Let’s start with a familiar salt: NaCl.
10 of 12
Determine Formulas
for Simple Salts
●
Determine the name of the following salt: NaCl
This molecule is composed of two different elements: Sodium & Chlorine.
Write the name of the metal atom first.
Sodium Chlorine
Write the name of the nonmetal with the suffix - ide
Chlor
ide
That’s it!
Naming is easy for salts that are composed of metals from Groups 1 & 2.
That’s because these metals react the same way every time.
Sodium always gives up one electron. Chlorine will accept one electron. So, sodium and chlorine will only react
11 of 12
Determine Formulas
for Simple Salts
●
Determine the name of the following salt: CaCl
2This molecule is composed of two different elements: Calcium & Chlorine.
Write the name of the metal atom first.
Calcium Chlorine
Write the name of the nonmetal with the suffix - ide
Chlor
ide
That’s it!
Naming is easy for salts that are composed of metals from Groups 1 & 2.
That’s because these metals react the same way every time.
Calcium always gives up two electrons. Chlorine will accept one electron. So, calcium and chlorine will only react
Determine Formulas
for Simple Salts
12 of 12
●
Write the name of the salt given the chemical
formula then click for the answers.
Formula
Name
Formula
Name
NaF
K
2O
MgO
BeI
2Li
2S
BaBr
2Sodium
Fluoride
Magnesium
Oxide
Lithium
Sulfide
Potassium
Oxide
Beryllium
Iodide
Barium
Bromide
1 of 13
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So far we have concentrated on salts whose metals
came from Groups 1 & 2.
●
These salts were easy to name and it was fairly
easy to determine their chemical formulas.
●
This is because the metals from Groups 1 & 2 are
very predictable. They do the same thing every
time they react.
●
Group 1 metals lose 1e- and take on a +1 charge.
Group 2 metals lose 2e- and take on a +2 charge.
●
But, what about all the other metals? What will
they do when they react and form salts?
Name Salts with
2 of 13
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All metals give up electrons when they react. (This
is characteristic of metals.) However, the metals
outside Groups 1 & 2 aren’t nearly as predictable.
Name Salts with
Multivalent Metals
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Some of these metals, like those in Groups 1 & 2,
will always give the same number of electrons.
Zinc always gives 2e- and takes on +2 charge
●
Other metals can give different numbers of
electrons in different situations.
Iron can give 2e- or 3e- and take on a +2 or +3 charge.
Name Salts with
Multivalent Metals
3 of 13
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When working with salts made up of metals outside
Groups 1 & 2, we have to make sure we know
which form of the atom we are dealing with.
●
In other words, we need to know the charge on the
atoms that make up the compound. (especially the
metals)
●
What would you do if you were asked to find the
charge on the Sodium ion in NaCl.
●
This is easy. Sodium is in Group 1. It’s always +1.
Name Salts with
Multivalent Metals
4 of 13
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Determine the charge on the nickel in the
compound NiBr
3.
Ni Br
3
Since Nickel is not in Group 1 or 2, we can’t be immediately sure of its charge.
But, we have some information that will help us figure it out.
First: NiBr3 is a molecule and by definition a molecule must have an
overall charge of zero
Overall Charge = Zero
Second: We don’t know how nickel reacted but we do know how
bromine reacted.
Nickel is a metal so it will give e-. That means bromine must take electrons.
Bromine is in Group 7 so it will
probably take 1 electron. Bromine takes 1 e-With these two pieces of information
we can begin to determine the charge on nickel in this compound.
Step1: Write the charge on one of the atoms in which you have the most confidence (Bromine in this case).
The charge on one Bromine = -1
- 1
Step2: Write the total charge on all of the bromines in this molecule.
There are 3 bromines in this molecule. One bromine is -1. So, three are –3.
- 3
Step 3: Balance out the total negative charges with positive charges.
We have 3 negative charges total. The charge on the whole atom is zero.
So, we must have 3 positive charges.
+ 3
Step 4: Distribute the positive charges to the remaining atoms.
We have 3 positive charges and only 1 nickel so all three positive charges must have come from the one nickel.
+ 3
The nickel ion, in this particular compound NiBr
3,
must have a positive 3 charge.
Charge on one Bromine
Charge on all 3 Bromines Total positive charge
Name Salts with
Multivalent Metals
5 of 13
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Determine the charge on one copper in the
compound Cu
2O.
Cu
2
O
Since copper is not in Group 1 or 2, we can’t be immediately sure of its charge.
But, we have some information that will help us figure it out.
First: Cu2O is a molecule and by definition a molecule must have an
overall charge of zero
Overall Charge = Zero
Second: We don’t know how copper reacted but we do know how
oxygen reacted.
Copper is a metal so it will give e-. That means oxygen must take e-.
Oxygen is in Group 6
so it will take 2 electrons. Oxygen takes 2 e-With these two pieces of information
we can begin to determine the charge on copper in this compound.
Step1: Write the charge on one of the atoms in which you have the most
confidence (Oxygen in this case). The charge on one Oxygen = -2
- 2
Step2: Write the total charge on all of the oxygens in this molecule.
There is only one oxygen in this molecule. One oxygen is -2.
- 2
Step 3: Balance out the total negative charges with positive charges.
We have 2 negative charges total. The charge on the whole atom is zero.
So, we must have 2 positive charges.
+ 2
Step 4: Distribute the positive charges to the remaining atoms.
We have 2 positive charges and two coppers so each copper must be +1
+ 1
Each copper, in this particular compound, Cu
2O,,
must have a positive 1 charge.
Charge on one Oxygen
Charge on all the Oxygens Total positive charge
Name Salts with
Multivalent Metals
6 of 13
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Determine the charge on the silver in the compound
AgF.
Ag F
Since silver is not in Group 1 or 2, we can’t be immediately sure of its charge.
But, we have some information that will help us figure it out.
First: AgF is a molecule and by definition a molecule must have an
overall charge of zero
Overall Charge = Zero
Second: We don’t know how silver reacted but we do know how
fluorine reacted.
Silver is a metal so it will give e-. That means fluorine must take e-.
Fluorine is in Group 7
so it will take 1 electron. Fluorine takes 1 e-With these two pieces of information
we can begin to determine the charge on silver in this compound.
Step1: Write the charge on one of the atoms in which you have the most confidence (Fluorine in this case).
The charge on one Fluorine = -1
- 1
Step2: Write the total charge on all of the fluorines in this molecule.
There is only one fluorine in this molecule. One fluorine is -1.
- 1
Step 3: Balance out the total negative charges with positive charges.
We have 1 negative charge total. The charge on the whole atom is zero.
So, we must have 1 positive charge.
+ 1
Step 4: Distribute the positive charges to the remaining atoms.
We have 1 positive charge and one silver so that silver must be +1
+ 1
Each silver, in this particular compound, AgF,
,
must have a positive 1 charge.
Charge on one Fluorine
Charge on all the Fluorines Total positive charge
Name Salts with
Multivalent Metals
7 of 13
●
Determine the charge on one iron in the compound
Fe
2S
3.
Fe
2
S
3
Since Iron is not in Group 1 or 2, we can’t be immediately sure of its charge.
But, we have some information that will help us figure it out.
First: Fe2S3 is a molecule and by definition a molecule must have an
overall charge of zero
Overall Charge = Zero
Second: We don’t know how iron reacted but we do know how
sulfur reacted.
Iron is a metal so it will give e-. That means sulfur must take electrons. Sulfur is in Group 6 so it will probably
take 2 electrons. Sulfur takes 2 e-With these two pieces of information
we can begin to determine the charge on iron in this compound.
Step1: Write the charge on one of the atoms in which you have the most
confidence (Sulfur in this case). The charge on one Sulfur = -2
- 2
Step2: Write the total charge on all of the sulfurs in this molecule.
There are 3 sulfurs in this molecule. One sulfur is -2. So, three are –6.
- 6
Step 3: Balance out the total negative charges with positive charges.
We have 6 negative charges total. The charge on the whole atom is zero.
So, we must have 6 positive charges.
+ 6
Step 4: Distribute the positive charges to the remaining atoms.
We have 6 positive charges and two irons so each iron must be +3
+ 3
Each iron, in this particular compound Fe2S3,
must have a positive 3 charge.
Charge on one Sulfur
Charge on all 3 Sulfurs Total positive charge
Name Salts with
Multivalent Metals
8 of 13
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Determine the charge on one of the metal atoms in
salts listed below.
Formula
Charge
Formula
Charge
Li
2O
Co
2O
3SnO
MnCl
3Cu
2S
HgCl
PbO
2CrO
3Li = +1
Sn = +2
Cu = +1
Pb = +4
Co = +3
Mn = +3
Hg = +1
Name Salts with
Multivalent Metals
9 of 13
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Dealing with these unpredictable metals is more
difficult than dealing with the Group 1 & 2 metals.
●
Naming salts composed of these metals is also a bit
more difficult.
●
A simple salt like NaCl is called Sodium Chloride.
●
Sodium will only give 1 electron. When chlorine
takes, it only takes one electron. Therefore, there is
only one way that sodium can react with chlorine.
●
Before we can name salts with unpredictable
Name Salts with
Multivalent Metals
10 of 13
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Let’s name two salts that are composed of a
multivalent metal.
Fe
2
O
3
Fe O
Both of these salts are composed of Iron (Fe) and Oxygen (O).
Iron Oxide
Iron Oxide
We can’t call both compounds Iron Oxide because they are two different compounds
with different formulas.
To properly name these two compounds, we have to know the form of the metal.
In other words, we have to find the charge on one metal atom in each compound.
Remember:
The overall charge on a molecule is zero. Start with the atom in which you have the most confidence. Oxygen in Group 6 is -2
Step 1:
Write the charge on one Oxygen.
Oxygen from Group 6 wants 2 electrons so it will take on a –2 charge.
- 2
- 2
Step 2:
Write the total charge on all the Oxygens. 1st Molecule 3 Oxygens each is –2 2nd Molecule 1 Oxygen which is -2
- 6
- 2
Step 3:
Balance out the total negative charges with an equal number of positive charges. The overall charge on a molecule is zero
+ 6
+ 2
Step 4:
Divide the total positive charge among the metal atoms.
1st Molecule 2 Fe 2nd Molecule 1Fe
+ 3
+ 2
The rest of the names for these two molecules is determined
by the charge on the metal.
Each iron atom in the first molecule has a +3 Charge.
This molecule is called Iron III Oxide (say: iron three oxide)
III
Each iron atom in the second molecule has a +2 Charge.
This molecule is called Iron II Oxide (say: iron two oxide)
Name Salts with
Multivalent Metals
11 of 13
●
Let’s name two salts that are composed of a
multivalent metal.
Cu
2
S
Cu Cl
2
Both of these salts are composed of Copper (Cu). One combines with Sulfur (S). The other combines with Chlorine (Cl).
Copper Sulfide Copper Chloride
We can’t just call these compounds Copper Sulfide and Copper Chloride because we don’t know which form of
copper is in which molecule.
To properly name these two compounds, we have to know the form of the metal.
In other words, we have to find the charge on a copper atom in each compound.
Remember:
The overall charge on a molecule is zero. Start with the atom in which you have the most confidence. Sulfur = -2 Chlorine = -1
Step 1:
Write the charge on 1 Sulfur & 1 Chlorine. Sulfur (Group 6) wants 2 e- –2 charge. Chlorine (Group 7) wants 1 e- -1 charge.
- 2
- 1
Step 2:
Write the total charge on all the nonmetals. 1st Molecule 1 Sulfur which is –2
2nd Molecule 2 Chlorines each is -1
- 2
- 2
Step 3:
Balance out the total negative charges with an equal number of positive charges. The overall charge on a molecule is zero
+ 2
+ 2
Step 4:
Divide the total positive charge among the metal atoms.
1st Molecule 2 Cu 2nd Molecule 1Cu
+ 1
+ 2
The rest of the names for these two molecules is determined
by the charge on the metal.
Each Copper atom in the first molecule has a +1 Charge.
This molecule is called Copper I Sulfide (say: copper one sulfide)
I
Each copper atom in the second molecule has a +2 Charge.
This molecule is called Copper II Chloride (say: copper two chloride)
Name Salts with
Multivalent Metals
12 of 13
●
Write the name of the salt given the chemical
formula then click for the answers. (Remember to
check charge on the metal).
Formula
Name
Formula
Name
SnF
2NiBr
3Au
2O
Au
2S
3PbS
2CrO
3HgCl
2Mn
2O
7Tin II
Fluoride
Gold I
Oxide
Lead IV
Sulfide
Nickel III
Bromide
Gold III
Sulfide
Chromium VI Oxide
Mercury II
Chloride
Name Salts with
Multivalent Metals
13 of 13
●
Why don’t we call NaCl; Sodium I Chloride
Α
Sodium is in Group 1. The metals in Group 1
always react the same way. They will only give up
one electron. So…
Sodium will always take on a positive 1 charge
(Na
+1). Since the charge on sodium is always +1,
there is no reason to include it in the name.
The same is true for Group 2 metals. They are
always +2. So, we can just write Calcium Oxide.
We don’t have to say Calcium II Oxide.
Examine Salts with
Polyatomic Ions
1 of 14
●
To this point, when we talked about forming
chemical bonds, we always said these bonds link
two or more atoms together to form a molecule.
●
A molecule has an overall charge of zero.
●
However, it is possible for atoms to form bonds but
still have a positive or negative overall charge.
●
These groups of bonded atoms can’t be called
molecules because they don’t balance out to zero.
●
The groups of bonded atoms are Polyatomic Ions.
Examine Salts with
Polyatomic Ions
2 of 14
●
Let’s look at the term Polyatomic Ion.
●
A Polyatomic Ion is two or more atoms that are
bonded together that have a charge.
●
The next slide contains some examples of
polyatomic ions. It includes the formula, the
charge, and the name.
“Poly-” means Many
“-Atomic” refers to atoms
Examine Salts with
Polyatomic Ions
3 of 14
●
Common Polyatomic Ions
Name
Formula
Charge
Ammonium
NH
4++1
Nitrite
NO
2--1
Nitrate
NO
3--1
Sulfate
SO
4-2-2
Phosphate
PO
4-3-3
Carbonate
CO
3-2-2
Bicarbonate
HCO
3--1
Examine Salts with
Polyatomic Ions
4 of 14
●
Polyatomic Ions can bond with other atoms to
form molecules.
●
Notice, most of the polyatomic ions have negative
charges and are composed of nonmetals.
●
These negative polyatomic ions often form bonds
with positive metal ions creating molecules that we
will classify as salts.
Examine Salts with
Polyatomic Ions
5 of 14
●
Write the formula for Calcium Sulfate.
The name of the molecule is Calcium Sulfate.
So we know there must be at least one Calcium atom.
Ca
We know what Calcium means in Calcium Sulfate, but what does Sulfate stand for?
Sulfate is the name of a polyatomic ion. SO
4 -2
SO
4
Calcium in Group 2 takes on a +2 charge.
The Sulfate ion always has a –2 charge.
+2 -2
One calcium with a +2 charge balances out one sulfate ion with a –2 charge.
So, a molecule of Calcium Sulfate has one Calcium ion bonded
to one Sulfate ion
The formula for Calcium Sulfate is CaSO4. One Calcium balances out one Sulfate
for an overall charge of zero.
Notice: the charges on the ions are not included in the chemical formula.
CaSO
4
How did we know that the formula for Calcium Sulfate was CaSO4 and not CaS.
CaS is Calcium Sulfide.
Polyatomic ions generally have names that end with something other than –ide. You can usually recognize the name of a
polyatomic ion because it ends with -ate, -ite, -ium.
Examine Salts with
Polyatomic Ions
6 of 14
●
Write the formula for Lithium Carbonate.
The name of the molecule is Lithium Carbonate.
So we know there must be at least one Lithium atom and at least one Carbonate ion (CO3-2).
Li CO
3
Lithium in Group 1 takes on a +1 charge. (Lithium wants to give 1e-)
Carbonate is the name of a polyatomic ion (CO3) that always has a –2 charge.
Will one lithium react with one Carbonate?
+1 -2
One Carbonate ion has a -2 charge but one Lithium has only a +1 charge. So…
To make a molecule with an overall charge of zero we need another positive charge.
That means we need another lithium. Lithium Carbonate has the formula Li2CO3.
It takes two Lithiums to balance out one Carbonate for an overall charge of zero.
Note: Carbonate refers to the CO3-2 ion Carbonide would refer to plain Carbon (C)
Examine Salts with
Polyatomic Ions
7 of 14
●
Write the chemical formula for Copper II Nitrate.
The name of the molecule is Copper II Nitrate.
So we know there must be at least one Copper atom and at least one Nitrate ion (NO3-1) .
Cu NO
3
The fact that it is Copper II tells us that we are dealing with Copper with a +2 charge.
Nitrate (NO3) is a polyatomic ion that always has a –1 charge.
Will one Copper react with one Nitrate?
+2 -1
One Copper has a +2 charge but one Nitrate has only a -1 charge. So…
To make a molecule with an overall charge of zero we need another negative charge. That means we need another Nitrate Ion.
Copper II Nitrate is Cu(NO3)2.
It takes two nitrate ions to balance out one Copper for an overall charge of zero. Notice: The nitrate ion is put in parentheses
with the subscript behind. Why?
Cu NO
3
NO
3
-1( )
2
It is written this way to show that we are involving two nitrate groups.
The parentheses show that the subscript goes with the entire polyatomic ion not just
Examine Salts with
Polyatomic Ions
8 of 14
●
Write the chemical formula for Iron II Phosphate.
The name of the molecule is Iron II Phosphate.
So we know there must be at least one Iron atom and at least one Phosphate ion (PO4-3) .
Fe PO
4
The fact that it is Iron II tells us that we are dealing with Iron with a +2 charge.
Phosphate (PO4) is a polyatomic ion that always has a –3 charge.
Will one Iron react with one Phosphate?
+2 -3
One Iron has a +2 charge but one Phosphate has a -3 charge. So…
To make a molecule with an overall charge of zero, we need more ions of each type.
Fe PO
4
PO
4
-3( )
2
In cases like these, look at the ion with the larger charge (PO4-3). One phosphate has a –3 charge.
You can’t balance that out with Fe+2 ions. One isn’t enough two is too many. So…
Since it won’t balance using only one Phosphate ion (PO4-3), try two phosphates. Two phosphate ions (PO4-3) will give you a
total of 6 negative charges.
Can you balance out a –6 with Fe+2 ions?
-6
You can you balance six negative charges with three with Fe+2 ions which equals +6.
This makes the charge
on the whole molecule equal to zero.
Fe
+2Fe
+2+6
Iron II Phosphate is Fe
3(PO4)2.
It takes three Irons to balance two
Phosphate ions for an overall charge of zero. Notice: The phosphate ion is put in
parentheses but the iron isn’t. Why?
3
It is written this way to show that we are involving two phosphate groups and three iron ions.
The parentheses show that the subscript goes with the entire polyatomic ion
Examine Salts with
Polyatomic Ions
9 of 14
●
Write the chemical formulas for the following
compounds then click for the answers.
Name Formula Name Formula
Lithium Bicarbonate
Chromium VI Nitrate Potassium
Sulfate
Cobalt II Phosphate Beryllium
Nitrite
Nickel III Carbonate Calcium
Acetate
Tin IV Phosphate
LiHCO
3
K2SO4
Be(NO
2)2
Ca(C
2H3O2)2
Cr(NO3)6
Co3(PO4)2
Ni2(CO3)3
Sn
3(PO4)4
Ion Formula
Ammonium NH4 +1
Nitrite NO2 -1
Nitrate NO3 -1
Sulfate SO4 -2
Phosphate PO4 -3
Carbonate CO3 -2
Bicarbonate HCO3 -1
Examine Salts with
Polyatomic Ions
10 of 14
●
You have been writing chemical formulas for salts
composed of polyatomic ions.
●
Next you will write the names of these salts when
given the chemical formula.
●
The good news is that most of the rules you learned
to this point still apply.
−
Name the most metallic element first
−
If the metal is mulitvalent, its charge will be in the name.
11 of 14
Examine Salts with
Polyatomic Ions
●
Name of the following salt: Mg(NO
3)
2This molecule is composed of Magnesium & Nitrate ions.
Write the name of the metal atom first.
Magnesium Nitrate
Write the name of the Polyatomic Ion That’s it!
Naming is simple for salts that are composed of metals from Groups 1 & 2.
That’s because these metals react the same way every time.
Magnesium always gives up 2 electrons. It always has a –2 charge.
The Nitrate ion always has a –1 charge. Since the charges are always the same, there
Examine Salts with
Polyatomic Ions
12 of 14
●
Name the following salt: Cu
3(PO
4)
2Cu
3
(PO
4
)
2
This salt is composed of
Copper (Cu) and Phosphate ions (PO4-3).
Copper Phosphate
We can’t just call this compound
Copper Phosphate because Copper is one of those unpredictable metals.
To properly name this compound, we have to know the form of the metal.
In other words, we have to find the charge on one copper atom in this compound.
Remember:
The overall charge on a molecule is zero. Start with the atom in which you have the
most confidence. PO4 has a –3 charge Step 1:
Write the charge on one Phosphate. The Phosphate ion always
has a negative three charge
- 3
Step 2:
Write the total charge on all the Phosphates There are two phosphates each has a –3 charge which gives a total of -6
- 6
Step 3:
Balance out the total negative charges with an equal number of positive charges. The overall charge on a molecule is zero
+ 6
Step 4:
Divide the total positive charge among the metal atoms.
There are three copper ions.
+ 2
The rest of the name for this molecule is determined by the charge on the metal.
Each Copper atom has a +2 Charge. This molecule is Copper II Phosphate
(say: copper two phosphate)
Examine Salts with
Polyatomic Ions
13 of 14
●
Write the name of the salt given the chemical
formula then click for the answers. (Remember to
check charge on the metal).
Formula Name Formula Name
Ba(NO2)2 NaC2H3O2
CuNO3 Au2(SO4)3
Sn
3(PO4)4 Cr(CO3)3
Hg(HCO3)2 Mn2(SO4)7 Barium
Nitrite
Copper I Nitrate
Tin IV Phosphate
Sodium Acetate
Gold III Sulfate
Chromium VI Carbonate
Mercury II
Bicarbonate Manganese VIISulfate
Ion Formula
Ammonium NH4 +1
Nitrite NO2 -1
Nitrate NO3 -1
Sulfate SO4 -2
Phosphate PO4 -3
Carbonate CO3 -2
Bicarbonate HCO3 -1
Examine Salts with
Polyatomic Ions
14 of 14
●
So far in this tutorial we have explored the group of
compounds called salts.
●
We determined chemical formula from the name.
●
We determined the name from the formula.
●
We found the charges on the ions in a salt.
●
We made salts using polyatomic ions.
●
Remember: Salts are composed of a metal and a
nonmetal and they tend to be ionically bonded.
●
In the rest of the tutorial we will explore three other
groups, Acids, Bases, and Nonmetal compounds.
Home
Examine Chemical
Formulas for Acids
1 of 9
●
In this section we wills study a group of compounds
called acids.
●
Acids are compounds that dissolve in water to
release Hydrogen Ions (H
+1).
●
Hydrogen has 1 proton & 1 electron. It must lose
that electron to form a hydrogen ion (H
+1).
●
A hydrogen ion, then, is just a proton which is very
reactive.
Examine Chemical
Formulas for Acids
2 of 9
●
Let’s analyze the formula for a simple acid.
H Cl
You can recognize an acid when you see its formula because it starts with an H.
When an acid is dissolved in water it breaks up into ions.
It is the Hydrogen ions that give an acid its acidic properties.
H
+1
Cl
-1
The formula for this acid was determined in the same way that
we found the formulas for salts.
Hydrogen ions always have a +1 charge. Chlorine will get 1e- so it has a –1 charge.
One positive Hydrogen Ion balances one negative Chlorine Ion. So…
The acid molecule shown above is formed from
one hydrogen and one chlorine. Naming a simple acid is
slightly different from naming salts. The name of a simple acid has three parts.
The name of a simple acid starts with the prefix
Hydro-Hydro
Next you name the nonmetal (chlorine in this case)
with the suffix -ic
chloric
Last, you add the word Acid
at the end.
Acid
Hydrochloric Acid (HCl) is a common strong acid.
Examine Chemical
Formulas for Acids
3 of 9
●
Are the formulas for these simple acids correct?
H F
H Br
Acids are composed of Hydrogen Ions. Both of these compounds
start with an H.
Hydrogen Ions always have a +1 charge. Both Fluorine & Bromine are in Group 7.
They both want to get 1 electron so they both tend to take on a –1 charge.
H
+1
F
-1
H
+1
Br
-1
One positive Hydrogen Ion balances one negative Fluorine in the 1st molecule.
One positive Hydrogen Ion balances one negative Bromine in the 2nd molecule. One hydrogen ion with one fluorine ion is
the correct formula for the 1st molecule. One hydrogen ion with one bromine ion is
the correct formula for the 2nd molecule. The formulas for both
Examine Chemical
Formulas for Acids
4 of 9
●
How would you name these simple acids?
H F
H Br
Both of these compounds start with H
so we know they are acids. The name of a simple acid starts with the prefix
Hydro-Hydro
Hydro
Next, name the nonmetal (Fluorine and Bromine)
with the suffix -ic
fluoric
bromic
Last, add the word Acid
to the end.
Acid
Acid
Hydrofluoric Acid is a very strong acid. It is so reactive,
it can be used to etch glass.
Hydrobromic Acid is a very strong acid. It is used to generate other organic compounds and in the manufacture of
Examine Chemical
Formulas for Acids
5 of 9
●
Acids can also be formed from hydrogen ions
bonding to negative polyatomic ions.
●
We will call these acids complex as opposed to the
simple acids we just studied.
●
Just like simple acids, complex acids release
hydrogen ions when they are dissolved in water.
●
The more hydrogen ions an acid releases, the
Examine Chemical
Formulas for Acids
6 of 9
●
Determine the correct formulas for two complex
acids made from the Nitrate and Phosphate ions.
NO
3
PO
4
Acids release hydrogen ions so these formulas must include
Hydrogen.
H
H
Now we know the types of ions that will compose these two molecules but to determine their formulas, we need
to know the charge on the ions. Hydrogen = +1
Nitrate (NO
3) = -1
Phosphate (PO
4) = -3
+1 -1 +1 -3
Just like any other molecule, an acid must have an overall charge of zero.
Will one H+1 balance one NO
3 -1?
Will one H+1 balance one PO
4 -3?
One positive hydrogen ion balances one negative nitrate ion.
So the correct formula is HNO
3
HNO
3
It will take three hydrogen ions (each +1) to balance one Phosphate ion (-3)
so the correct formula is H
3PO4
H
+1
H
+1
Examine Chemical
Formulas for Acids
7 of 9
●
Determine the correct formula for complex acids
created from the polyatomic ions below.
Polyatomic Ion
Formula for the Acid
Sulfate
SO
4-2Carbonate
CO
3-2Acetate
C
2H
3O
2-1Examine Chemical
Formulas for Acids
8 of 9
●
The table below shows the formula, names, and
uses for some common complex acids.
Formula
Name
Use
HNO
3H
2SO
4H
3PO
4H
2CO
3HC
2H
3O
2Nitric Acid
Strong Acid used tomake other chemicals
Sulfuric
Acid
Strong Acid Used as battery acid
Phosphoric
Acid
Weak Acid Used in Pickling
Carbonic
Acid
Weak Acid
In carbonated drinks
Acetic Acid
Weak Acid VinegarNotice:
The prefix Hydro- is dropped from
the names of complex acids
Examine Chemical
Formulas for Acids
9 of 9
●
What is it about an acid that gives it its acidic
properties?
Α
A compound is considered to be an acid if it
releases hydrogen ions H
+1when dissolved in
water. The more hydrogen ions that are released
the stronger is the acid. Hydrogen ions are very
reactive particles which makes acids very reactive
compounds.
Home
1 of 6
Examine Chemical
Formulas for Bases
●
In this section we will study a group of compounds
called Bases.
●
The term base may be new but the terms alkaline or
caustic may be familiar. They all refer to bases.
●
Bases are compounds that dissolve in water to
release a particular polyatomic ion (OH
–1)
●
The OH
-1ion is called the Hydroxide Ion. Notice it
ends with –ide, this is an exception to our rule.
Examine Chemical
Formulas for Bases
2 of 6
●
Let’s analyze the formula for a Base.
Na OH
You can recognize a base when you see its formula because it ends with an OH. When a base is dissolved in water
it breaks up into ions.
It is the hydroxide ions (OH-1) that give a base its basic properties.
Na
+1
OH
-1
The formula for this base was determined in the same way that
we found the formulas for salts.
Hydroxide ions always have a -1 charge. Sodium will give 1e- so it has a +1 charge.
One positive Sodium Ion balances one negative Hydroxide Ion. So…
The base molecule shown above is formed from
one sodium and one hydroxide. Naming a base is the same
as naming salts composed of polyatomic ions.
Name the metal first.
Sodium
Next name the polyatomic ion. The polyatomic ion
associated with bases is the Hydroxide ion.
Hydroxide
Sodium Hydroxide (NaOH) is a common strong base.
Examine Chemical
Formulas for Bases
3 of 6
●
Determine the correct formula for the base
Calcium Hydroxide
Ca
OH
If the name is Calcium Hydroxide, then we must have
at least one Calcium and at least one Hydroxide ion. To determine the correct formula,
we have to know the charges
on the ions that make up the molecule. Ca (Group 2) = +2 OH = -1
+2
-1
Molecules have an overall charge of zero.
Will one calcium balance one hydroxide?
One Ca is +2 while one OH is –1. So, we will need two Hydroxide ions
to balance each Calcium.
OH
-1
The formula for Calcium Hydroxide
is Ca(OH)2
Ca(OH)
2
Remember the parentheses. They tell you that we need
Examine Chemical
Formulas for Bases
4 of 6
●
Name the base that was formed from the
multivalent metal shown in the compound below.
Fe (OH)
3
This base is formed from Iron and the Hydroxide ion.
Iron
Hydroxide
We can’t just call this base Iron Hydroxide because iron is multivalent.
We need to know the charge on this particular iron.
To find the charge on iron, start with the charge on the hydroxide ion.
Remember, the overall charge must be zero. Step 1
Write the charge on one hydroxide ion. Hydroxide is always has a –1 charge.
-1
Step 2
Write the total charge on all the hydroxide ions
Three hydroxides each has a –1 charge = -3.
-3
Step 3
Balance the three negative charges with three positive charges for an overall charge of zero.
+3
Step 4
Divide the positive charges among the remaining atoms. There is only one iron so
that iron must have a +3 charge.
+3
The name for Fe(OH)
3
is Iron III Hydroxide (say: iron three hydroxide)
Examine Chemical
Formulas for Bases
5 of 6
●
Fill in the missing pieces of the table below.
Name
Formula
LiOH
Potassium Hydroxide
Magnesium Hydroxide
Ni(OH)
2Copper II Hydroxide
Aluminum Hydroxide
(Al is not multivalent.) (What charge will it take on?)
Lithium Hydroxide
KOH
Mg(OH)
2Nickel II Hydroxide
Cu(OH)
2Al(OH)
3Examine Chemical
Formulas for Bases
6 of 6
●
What is it about a base that gives it its basic
properties?
Α
A compound is considered to be a base if it releases
hydroxide ions OH
-1when dissolved in water. The
more hydroxide ions that are released the stronger
is the base. Hydroxide ions are very reactive
particles with makes bases very reactive
compounds. Bases are sometimes called alkaline
or caustic. They are used in cleaning compounds,
for fertilizer, and as antacids.
Name Nonmetal
Compounds
1 of 6
●
In this section, we will look at a few compounds
that are composed entirely of nonmetals.
●
We will learn the basics of naming nonmetal
compounds.
●
We won’t determine the chemical formulas for
nonmetal compounds from the charges.
●
This is because many nonmetals are multivalent.
●
Even those nonmetals in Groups 6 & 7 that we
counted on to be –2 and –1, can do many different
things when they react with other nonmetals.
Name Nonmetal
Compounds
2 of 6
1 H 1.0 2 He 4.0 3 Li 7.0 4 Be 9.0 5 B 11.0 6 C 12.0 7 N 14.0 8 O 16.0 9 F 19.0 10 Ne 20.0 11 Na 23.0 12 Mg 24.5 13 Al 27.0 14 Si 28.0 15 P 31.0 16 S 32.0 17 Cl 35.5 18 Ar 40.0 19 K 39.0 20 Ca 40.0 21 Sc 45.0 22 Ti 48.0 23 V 51.0 24 Cr 52.0 25 Mn 55.0 26 Fe 56.0 27 Co 59.0 28 Ni 58.5 29 Cu 63.5 30 Zn 65.5 31 Ga 69.5 32 Ge 72.5 33 As 75.0 34 Se 79.0 35 Br 80.0 36 Kr 84.0 37 Rb 85.5 38 Sr 87.5 39 Y 89.0 40 Zr 91.0 41 Nb 93.0 42 Mo 96.0 43 Tc 98.0 44 Ru 101.0 45 Rh 103.0 46 Pd 106.5 47 Ag 108.0 48 Cd 112.5 49 In 115.0 50 Sn 118.5 51 Sb 122.0 52 Te 127.5 53 I 127.0 54 Xe 131.0 55 Cs 133.0 56 Ba 137.5 57 La 139.0 72 Hf 178.5 73 Ta 181.0 74 W 184.0 75 Re 186.0 76 Os 190.0 77 Ir 192.0 78 Pt 195.0 79 Au 197.0 80 Hg 200.5 81 Tl 204.5 82 Pb 207.0 83 Bi 209.0 84 Po 209.0 85 At 210.0 86 Rn 222.0 Group 1
2 3 4 5 6 7
8
Noble Gases
Metals
Nonmetals
Name Nonmetal
Compounds
3 of 6
●
Name the two familiar nonmetal compounds below.
CO
CO
2
Naming nonmetal compounds is different from naming the salts, acids, and bases.
We will use Greek prefixes to show the number of each atom in the molecule.
Prefix Number
Mono - One Di - Two Tri - Three Tetra - Four Penta - Five Hexa - Six
Both of these compounds are composed of
Carbon and Oxygen.
Carbon
Oxygen
Carbon
Oxygen
The least metallic atom, Oxygen in this case,
gets the suffix –ide Oxygen becomes Oxide
ide
ide
Use the Greek prefixes, at the right, to show
how many atoms of each element are in the molecule.
In the first molecule (CO), there is one Oxygen =
Mono-In the second molecule (CO2), there are two Oxygens =
Di-Mono
Di
o
There is one Carbon in each molecule. When there is only one of the first atom
we don’t use the mono prefix.
It is understood that there is one carbon. The first molecule (CO) is called
Carbon Monoxide