Transcript Naming and Formula Writing

Naming and Formula
Writing
• “The sum of the oxidation numbers must
equal zero.”
• You need to learn the majority of the
symbols and charges on the oxidation
number sheet
• Naming: The basics
• For those elements and ions whose
oxidation numbers that do not
vary, simply name the positive ion and
then the negative one and
You are done.
• Example NaCl is Sodium Chloride.
• Traditional (old) system:
• Is used with those metallic elements that
can have more than one oxidation number.
That would be most of the “d”
block metals.
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FeCl2
is Ferrous Chloride
Use the ion whose oxidation number does not change to determine which
form of iron was used.
Since chlorine is always a negative one and there are two chlorine atoms in
the formula, the iron must be the plus two variety because the sum of the
oxidation numbers must equal zero.
This form of iron is called Ferrous thus the name is
Ferrous Chloride.
• Stock System:
•
Is used with the same elements as the
tradition system, and is easier to use when
going from name to formula. In this system
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FeCl2 would be Iron II Chloride
• The oxidation number of iron is
determined the same as above however in
this system a roman numeral is used to
denote the Oxidation number of the
metal instead of the “ic” or “ous” ending.
Do not use roman numerals with elements
who’s oxidation numbers don’t vary.
• Binary Naming:
• Is used with binary compounds
(containing only two elements)
• Both of whose oxidation numbers can
vary. That makes determining the
oxidation numbers of each difficult.
• There are five simple steps to this system.
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As2O5
Is Diarsenic pentoxide
1. Prefix for the number of atoms of the first element.
In is example its “Di” (never use the prefix mono
For the first element.) It is considered redundant.
2. The full name of the first element “arsenic”
3. Prefix for the number of the atoms of the second
element “pent” (There must be a prefix before the
second element.)
• 4. The root of the name of the second element. “ox”
• 5. Add the ending “ide” and it’s done
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Di arsenic pent ox ide
The prefixes
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One
Two
Three
Four
Five
= mono
= di
= tri
= tetra
= penta
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Six
= hexa
Seven = hepta
Eight = octa
Nine = nona
Ten = deca
• Formula writing is the reverse:
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Calcium Nitrate
is Ca (NO3)2
Ca is a +2 and NO3 is a -1 so two
NO3 groups are needed to make the sum
of the oxidation numbers equal zero.
• To show that put the NO3 group in
parenthesis and add the subscript 2
• I recommend that you write in the charges
when you write formulas it will help you
learn the charges and prevent careless
• mistakes.
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Ca+2(NO3-1)2
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Ca+2(NO3-1)2
• Use the criss-cross method to determine
the subscript numbers. It works most of
the time, but always check for the common
denominator.
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Page 233 Chemistry
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Prentice Hall
The old system
• Ferric Sulfate
With the old system you
have to know that Ferric is Fe +3 and that
sulfate is SO4 -2 in order to start. So you
need to know the oxidation sheet. Again
the oxidation numbers must equal zero. To
do that the common denominator of 6 is
required.
Again criss-cross
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2 x 3 = 6 and 3 x 2 =6
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Fe+32(SO4-2)3
Stock system
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Iron III Sulfate is the same as above
except that you are told in the name that
iron is a + 3 so you did not have memorize
that detail.
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Fe+32(SO4-2)3
• The roman numeral III is the + 3 by the
iron.
Binary System
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Dinitrogen Trioxide
Just write down what the name says.
Two nitrogen and three oxygen
N 2O 3