Unit II: Intro to Formulas
Elements and
Ionic Compounds
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A. Element OR Compound?
Elements:
Formulas only contain ONE symbol
Which means only ONE capital letter.
Names are only ONE word long.
Compounds:
Formulas contain two or more symbols.
Which means more than one capital
letter.
Names are TWO words long.
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Elements: A Review
We already learned that:
Most element formulas consist of the
element symbol and nothing more.
(Al, Cu, Ne, Au, etc.)
Seven elements are “diatomic” and always
pair up in the elemental state:
(H2, N2, O2, F2, Cl2, Br2, I2)
Elements go by their own names
But sometimes Carbon is sneaky.
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Compounds
There are different types of chemical
compound. For this unit, we are only
learning IONIC compounds:
Ionic compounds form by transfer of
valence electrons.
Valence electrons are the
outermost electrons in an atom.
This atom has lots of electrons.
But only ONE in its VALENCE.
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The periodic table
The table is organized so similar
elements are together.
Similar properties are usually due to
similar # of valence electrons.
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Groups of similar elements have special names:
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# valence electrons
increases, left to right:
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Sodium has 1 valence electron
Chlorine has 7 valence electrons
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Lewis Dot Structures
Show ONLY valence electrons
Each electron is shown as a dot.
Electrons come in pairs– top, bottom, left,
& right of symbol.
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Valence Electrons & Stability
Eight valence electrons = a “full octet”
Atoms with a full octet are the most stable
This is why the noble gases are “noble”
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Valence Electrons & Stability
All other elements work to achieve a
“full octet” by gaining, losing, or
sharing electrons:
Atoms are like onions– the electrons come in layers.
The sodium now has zero electrons in the diagram, but there was
already a full octet in the next lower layer, so it is stable now.
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Valence Electrons & Stability
Gaining or losing electrons gives the
atom a charge.
Charged particles are called IONS.
If one atom loses electrons, another must gain
them.
Even tiny electrons are matter, and can’t be
created or destroyed!
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Valence Electrons & Stability
An atom that loses electrons becomes
positively charged.
This is a cation.
(Subtracting a negative
makes a positive!)
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Cations are Positive
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Valence Electrons & Stability
An atom that gains electrons becomes
negatively charged.
This is an anion.
Note: the name changes
to the “–ide” form when it
becomes negative!
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Barium is in column 2 and has 2
valence electrons
Sulfur is in column 16 and has 6
valence electrons
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To get full octets:
Barium must lose TWO electrons
Sulfur must gain TWO electrons
Key Point: Ion charge is based on how
many electrons must be gained or lost to
get a full octet.
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Valence Electrons & Stability
Main Group Ion Charges
1+
0
2+
3+ 4± 3- 2- 1-
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Ionic Compounds
Form because opposite charged ions
attract each other.
Cations and anions arrange themselves in
a “crystal lattice.”
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Ionic Crystals
A “crystal lattice”
Is a 3-D grid of ions– the
general structure of ionic
compounds
Is hard to melt
due to attraction
between anions
and cations
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C. Ionic Nomenclature
Ionic Names: Cations
Write the name of the cation first.
Stock System: Use Roman numerals to
show the cation’s charge if more than one
is possible.
D-block (transition metals)
Poor metals
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C. Ionic Nomenclature
How do you know the Roman numeral?
Math! (The overall charge must equal
zero.)
oFeCl2
•Cl gets a charge of: 1- (because it is in column 17)
•Fe must have a charge of ____ to make the
compound = 0
oThis is Iron (II)
2+
Chloride
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C. Ionic Nomenclature
Fe2 S3
There are only two capital letters, so no
polyatomic ion to worry about.
I look up S on the periodic table
S
oColumn 16:
o6 valence electrons, 2- charge
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C. Ionic Nomenclature
Fe2 S3 = iron ( ? ) sulfide
6+
6-
=0
( 3+)2 + (2- ) 3
Fe2 S3
Iron (III) sulfide
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C. Ionic Nomenclature
Fe2 (CO3)3 = iron ( ? ) carbonate
6+
6-
=0
(3+)2 + (2- ) 3
Fe2 (CO3)3
Iron (III) carbonate
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C. Ionic Nomenclature
Fe CO3 = iron ( ? ) carbonate
2+
2-
=0
( 2+)1 + (2- ) 1
Fe CO3
Iron (II) carbonate
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C. Ionic Nomenclature
Ni2 CO3 = nickel ( ? ) carbonate
2+
2-
=0
(1+)2 + (2- ) 1
Ni2 CO3
Nickel (I) carbonate
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C. Ionic Nomenclature
Ionic Names: Cations
Roman numerals are NOT needed for:
Group 1 & 2
o(1+, 2+)
Ag, Zn, Al
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C. Ionic Nomenclature
Ionic Names: Anions
Monatomic anion names are the first
syllable of the element name, then -ide.
(Chloride, oxide, phosphide, nitride, etc)
Polyatomic ions have special names.
(Chart on the back of your periodic table.)
Do NOT change the ending of
polyatomic ions.
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C. Ionic Nomenclature
Overview:
Consider the following:
Does it contain a polyatomic ion?
o2 elements  no; ending is “-ide”
o3+ elements  yes; ending is -ate -ite
Does it contain a Roman numeral?
oCheck the table: is the metal NOT in
Groups 1 or 2 (or Ag, Zn, Al)?
NO numerical prefixes!
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C. Ionic Nomenclature
NaBr
sodium bromide
Na2CO3
sodium carbonate
FeCl3
iron(III) chloride
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