Post on 29-Dec-2015
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Elements andIonic Compounds
Unit II: Intro to Formulas
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.LPChem1415
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.LPChem1415
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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.
The periodic table
The table is organized so similar
elements are together.
Similar properties are usually due to
similar # of valence electrons.
Groups of similar elements have special names:
# valence electrons
increases, left to right:
12 345678
Sodium has 1 valence electron
Chlorine has 7 valence electrons
12 345678
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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
12 345678
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!
Barium is in column 2 and has 2
valence electrons
Sulfur is in column 16 and has 6
valence electrons
1 2 3 4 5 6 7 8
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+
2+ 3+ 4± 3- 2- 1-
0
Form because opposite charged ions attract each other.
Ionic Compounds
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
2+ oThis is Iron (II)
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
oColumn 16:
o6 valence electrons, 2- charge
S
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C. Ionic Nomenclature
Fe2 S3 = iron ( ? ) sulfide
Fe2 S3
2-
6-
( ) 3
= 06+
( )2 +3+
Iron (III) sulfide
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C. Ionic Nomenclature
Fe2 (CO3)3 = iron ( ? ) carbonate
Fe2 (CO3)3 2-
6-
( ) 3
= 06+
( )2 +3+
Iron (III) carbonate
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C. Ionic Nomenclature
Fe CO3 = iron ( ? ) carbonate
Fe CO3 2-
2-
( ) 1
= 02+
( )1 +2+
Iron (II) carbonate
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C. Ionic Nomenclature
Ni2 CO3 = nickel ( ? ) carbonate
Ni2 CO3 2-
2-
( ) 1
= 02+
( )2 +1+
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
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.
Ionic Names: Anions
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C. Ionic Nomenclature
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!
Overview:
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C. Ionic Nomenclature
NaBr
Na2CO3
FeCl3
sodium bromide
sodium carbonate
iron(III) chloride