Chapter 7
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An ion is an atom that has gained or lost
electrons from the valence shell.
Valence electrons are the electrons contained
in the highest occupied energy level
◦ These electrons will mostly determine the chemical
properties of the element
◦ For representative elements, group # = # valence
electrons
◦ Exception is Helium with 2 valence e-
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Diagrams that show the number of valence
electrons
Also called Lewis Dot Diagrams
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Gilbert Lewis recognized that Noble Gases are
inert.
These elements have a full s and p sublevel and
with the exception of Helium have 8 valence e-.
He realized that atoms will bond in order to
achieve noble gas e- configuration.
Atoms of metals tend to lose their valence e-,
leaving a complete octet in the next lowest
energy level. Atoms of nonmetals tend to gain
e- or to share e- with one another to complete
an octet.
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An atom’s loss of valence e- produces a
cation, or (+) charged ion.
Metals have relatively low ionization energy.
It requires less energy to remove 1,2,3, or 4
valence electrons.
Metals have relatively low electronegativity
and are not likely to gain electrons.
Metals will typically lose all valence electrons
and have a charge equal to the number of
electrons lost.
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Atoms will lose valence e- in order to achieve
the electron configuration of the nearest
noble gas.
1
Na 1s 2 s 2 p 3 s  Na 1s 2 s 2 p
2
2
6
Na  Na
.
1

e

2
2
6
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Transition metals do not always form Noble
gas electron configuration when forming
cations.
Because of the partially filled d sublevel, they
form pseudo noble gas configurations
Silver will form a +1 ion
Copper can form +1 or +2
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Once electrons are removed from a neutral
atom a positive charge will exist.
For cations, the name of the metal is the
same as the name of the cation.
Al is called aluminum.
Al+3 is still called aluminum.
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The gain of negatively charged electrons by a
neutral atom produces an anion.
Most nonmetals have more than 4 e- in the
valence shell.
They will gain e- in order to achieve the noble
gas configuration of the nearest noble gas.
 e-
Cl 1s 2 s 2 p 3 s 3 p   Cl 1s 2 s 2 p 3 s 3 p
2
2
6
2
5
-
2
2
6
2
6
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When atoms from group 7A gain e-, they will
have a charge of -1. These anions are called
halide ions.
Once a nonmetal gains electrons, the name of
the ion will be different from the name of the
neutral ion.
For monatomic anions, drop the ending and
add –ide.
Ex: Oxide, Phosphide, Sulfide, Fluoride,
Chloride
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Compounds composed of cations and anions
are called ionic compounds.
Ionic compounds are typically neutral.
The electrostatic forces that hold ionic
compounds together are called ionic bonds.
Just like when forming ions, ionic compounds
consist of cations and anions seeking a
complete octet.
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A chemical formula shows the kinds and
numbers of atomic in the smallest
representative unit of a substance.
Ionic compounds are not typically found as
just one unit. Typically a regular, repeating
pattern of ionic bonds will exist.
In other words, a compound like NaCl will be
connected to several other NaCl units.
A formula unit is the lowest whole-number
ratio of ions in an ionic compound.
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Write the formula for both the cation and the
anion.
Eliminate the (+) and (-) charges.
“Drop and drag” the numbers remaining as
subscripts for the formula unit.
No charges will remain in the final formula.
Mg
2
Cl
MgCl
1
2
Al
3
S
2
Al 2 S 3
Atoms
Combining
Sodium and
Sulfur
Barium and
Oxygen
Calcium and
Phosphorus
Potassium and
Nitrogen
Aluminum and
Oxygen
Lithium and
Iodine
Ion Formulas
Formula
Name
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Most ionic compounds are crystalline solids
at room temperature.
◦ Arranged in regular, repeating, 3-D patterns
◦ Structure is related to coordination number
(number of oppositely charged ions surrounding an
ion.)
◦ See some examples here.
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Ionic compounds have high melting points.
Ionic compounds conduct an electric current
when melted or dissolved in water.
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Metals are made up of closely packed cations
rather than neutral atoms.
The valence electrons of metals can be
modeled as a sea of electrons.
◦ Valence e- are mobile and can drift freely
◦ Metals are ductile and malleable
◦ Metals conduct electricity
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Metal atoms are arranged in very compact
and orderly patterns.
Check out this cool Nova Explanation of
metals!
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Alloys are mixtures composed of two or more
elements, at least one of which is a metal.
Alloys are important because their properties
are often superior to those of their
component elements.
◦ Sterling silver: silver and copper
◦ Bronze: copper and tin
◦ Steel: iron, carbon, boron, chromium, manganese,
molybdenum, nickel, tungsten, and vanadium