CHEM 107-001
Summer 2017
Dr. Eric C. Booth
Ions part 1
The Octet Rule
 In
reactions, elements try to
combine in a way that gives them
the same electron configuration as
the nearest noble gas
 Elements (in upper rows, L & R
columns) that react this way tend
to surround themselves with 8
valence electrons
 This is called the octet rule
 Exceptions: H, He (2 electrons)
The Octet Rule
 Example:
NaCl
Na
Cl
The Octet Rule
 Example:
NaCl
+
Na
Cl
-
Octets and Electron Dots
 In
a diagram of the compounds that
are formed:
 atoms
that attain a noble-gas
configuration by receiving electrons
get eight dots
 atoms that achieve a noble-gas
configuration by losing electrons get
no dots
 exchange electrons between atoms
Ions
 Electrically
charged atoms
 Ions of metal atoms form noble gas
configuration by losing electrons
 Positive ions also called cations
 Ions of nonmetal atoms gain
electrons to form noble gas
configuration
 Negative ions also called anions
Positive Ions
2
major 1-atom cation classes:
 Alkaline
ions (Li+, Na+, K+, Rb+, Cs+)
Na+,
K+ critical for proper nervous
system function
 Alkaline
earth ions (Mg2+, Ca2+, Sr2+,
Ba2+)
Mg2+,
Ca2+ essential nutrients
Ba2+ toxic when dissolved in body
 You
should know these ions cold
Negative Ions
3
major 1-atom anion classes:
 Halide
ions (F-, Cl-, Br-, I-)
fluoride
used to prevent cavities
chloride has many biological roles
iodide needed for thyroid (metabolism)
(O2-) and sulfide (S2-) ions
 Nitride (N3-) and phosphide (P3-)
ions
 Oxide
 Again,
have these down cold
Group Numbers and Charges
the left-hand “block” of the
periodic table, element’s column
number = number of ion’s
positive charges
 In the right-hand “block” of the
periodic table, number of
columns nonmetallic element is
away from noble gas = number of
ion’s negative charges
 In
S block
Group Numbers and Charges
the left-hand “block” of the
periodic table, element’s column
number = number of ion’s
positive charges
 In the right-hand “block” of the
periodic table, number of
columns nonmetallic element is
away from noble gas = number of
ion’s negative charges
 In
S block
How Ion, Atom Sizes Compare
 When
a positive ion forms, atom
loses electrons from its upper,
outer energy level
 this
makes positive ions smaller than
the atoms they form from
How Ion, Atom Sizes Compare
How Ion, Atom Sizes Compare
 When
a positive ion forms, atom
loses electrons from its upper,
outer energy level
 this
makes positive ions smaller than
the atoms they form from
 When
a negative ion forms, atom
gains electrons in its upper level
 since
electrons repel each other,
negative ions are larger than the
atoms they form from
How Ion, Atom Sizes Compare
Ionic Compound Properties
 Drastically
different from the
elements that form them
 Ionic compounds form crystals
at room temperature
 hard
and brittle (e.g. rock salt)
 Melting,
boiling points very high
melts @ 800 °C: Na, 98 °C
 due to very strong attractive
forces between cations and anions
 NaCl
How Many Of Each Ion?
 An
anion must always combine w/
some cation (opposites attract)
 The total charge of an ionic
compound is always zero
 # of positive charges contributed
all the cations must = # of negative
charges contributed by all anions
 Adjust the numbers of anions and
cations until their charges cancel
From Charges To Formulas
 Given
the charge on one ion,
you can determine how many
of the oppositely-charged ions
will be needed to make a
compound
+2
Mg
Cl
From Charges To Formulas
 Given
the charge on one ion,
you can determine how many
of the oppositely-charged ions
will be needed to make a
compound
+2
Mg
Cl2
Ionic Formula Examples
 What
is the formula of the
compound that is created when
you combine ions of:
 potassium
 barium
and iodine?
and fluorine?
 aluminum
and oxygen?
2-element Ionic Compound
Names
 Find
anion, cation
 Write down the cation’s name first
 The cation’s name is name of the
corresponding element
 Write anion’s name second
2-element Ionic Compound
Names (cont’d)
 To
get the anion’s name:
 take
corresponding element name
 subtract the ending
 add -ide in place of the ending
If Multiple + Ions Possible…
 Some
metals (especially transition
metals) form more than one cation
 If ionic compound has such metal,
can’t get formula from name only
 Example: “iron chloride” could be
FeCl2 or FeCl3 (or even both)
 Write these cations’ charges in
Roman numerals following names
 iron
(II) chloride = FeCl2
 iron (III) chloride = FeCl3
From Names To Formulas:
Demonstration
 Lead
(IV) chloride
 In this specific compound, any lead
atom will have 4 positive charges
 Chloride ion always has one
negative charge
 To get a compound where all
charges cancel, use one 1 Pb and
four Cl: PbCl4
Name To Formula: Examples
 Give
the formulas of the following
compounds:
 gold
(III) nitride
 lead
(II) oxide
 nickel
(II) phosphide