Chemical Bonding
Ionic Bonding in Review
• Ionic compounds tend to form as crystals
– These crystals have a specific shape
• Arrangement of the ions that make up the ionic
compound
• Ratio of the ions in the compound
• Size of the ions themselves
– NaCl – cubic
– Al2O3 – Ruby – Hexagonal
Crystal Structure
Crystal Structure
Properties of Ionic Compounds
• High Melting Points
• Poor conductor when they are in the solid
state
• Good conductor when they are melted
• Tend to shatter when they are struck with
a hammer
Covalent Bonding
• A transfer of electrons does not tend to take
place between nonmetals
• These nonmetals tend to share their electrons to
complete their valence (outer) shells
• When atoms share electrons they form a
covalent bond
– One pair shared – single bond (hydrogen)
– Two pairs shared – double bond (oxygen)
– Three pairs shared – triple bond (nitrogen)
Molecules
• A molecule is a neutral group of atoms
that are joined by one or more covalent
bonds
– They are held together by the attraction
between the shared electrons and the protons
in each nucleus
Covalent Bonding
• Ways to represent covalent bonds
– Electron Dot
– Structural Formula
– Space-filling model
– Electron Cloud Model
Models for Covalent Molecules
Unequal Sharing
• Elements to the right have a greater attraction
for electron than those on the left
• Elements at the top of the group have a greater
attraction for electrons than those below
• Polar Covalent Bond – covalent bond in which
the electrons are not shared equally
– The atom with the greater attraction for the electrons
has a partial negative charge and the atom with the
weaker attraction for electrons has a partial positive
charge
Unequal Sharing
How Do we Know?
• If a molecule has only two atoms (different
elements) it will always be polar
• If a molecule has more than two atoms
then the answer is not obvious
– If the molecules are linear they will be
nonpolar (usually contain double or triple
bonds)
Attraction between molecules
• The attraction between polar molecules is
stronger than the attraction between
nonpolar molecules
– Water
Naming Molecular Compounds
• The name of a molecular compound
describes the type and number of atoms in
a molecule of the compound
– Most metallic element appears first (further
left or if in the same group closer to the
bottom
– Name of second element changed to end in
IDE
– Use prefix to indicate the number atoms of
each element
Prefixes to use
Examples
• We never use a prefix on the first element
if it contains only one atom (never use
mono at the beginning)
• CO2 - Carbon Dioxide
• P2F4 – Diphorphorous tetrafluoride
• CO – Carbon monoxide
• CF4 – Carbon tetrafluoride
Naming Binary Ionic Compounds
• Give the name of the cation (metal) first
– No change to the name – just the name of the element
• Give the name of the anion (nonmetal) second changing
the end to “ide”
–
–
–
–
–
–
–
–
Chlorine = chloride
Fluorine = fluoride
Bromine = bromide
Oxygen = oxide
Nitrogen = nitride
Phosphorous = phosphide
Iodine = iodide
Sulfur = sulfide
• NOTE – THE NUMBERED SUBCRIPTS AREN’T USED
WHEN NAMING BINARY IONIC COMPOUNDS!
Practice Naming
• Give the correct name to the following
binary ionic compounds
– Li2S
– MgO
– CaCl2
– SrF2
– KBr
– Na3P
– Al2O3
Answers
•
•
•
•
•
•
•
Li2S – Lithium Sulfide
MgO – Magnesium Oxide
CaCl2 – Calcium Chloride
SrF2 – Strontium Fluoride
KBr – Potassium Bromide
Na3P – Sodium Phosphide
Al2O3 – Aluminum Oxide
Practice Formula Writing
• Write the chemical formula for the following
binary ionic compounds
–
–
–
–
–
–
–
–
Lithium Nitride
Rubidium Fluoride
Sodium Iodide
Beryllium Nitride
Magnesium Sulfide
Calcium Bromide
Aluminum Nitride
Barium Oxide
Answers
•
•
•
•
•
•
•
•
Lithium Nitride – Li3N
Rubidium Fluoride - RbF
Sodium Iodide - NaI
Beryllium Nitride – Be3N2
Magnesium Sulfide - MgS
Calcium Bromide – CaBr2
Aluminum Nitride - AlN
Barium Oxide - BaO
Naming when there are transition
metals
• Some of the transition metals exist as
ions with more than one charge
– Copper can be + 1 or + 2
– Iron can be + 2 or + 3
– Lead can be +2 or +4
– Chromium can be +2 or + 3
– Titanium can be +2, +3, or + 4
– Mercury can be +1 or +2
Continued
• When these elements appear in an ionic
compound we must use a Roman numeral after
the name of the cation to indicate which form
(charge) of the ion it is when we are naming
these ionic compounds. The Roman number
tells us the number of the positive charge
(Again remember we must have a total net
charge of zero)
– Copper (I) oxide = Cu2O
– Copper (II) oxide = CuO
Now the tricky part continued
• When asked to give the formula remember
that the Roman numeral tells us the
charge on the cation.
– Iron (III) oxide
– Mercury (II) chloride
– Lead (IV) nitride
Polyatomic ions
SiO3-2 - Silicate
Naming Ionic Compounds
Containing Polyatomic Ions
• Works the same as simple binary ionic
compounds except that in place of the
single element anion you give the name of
the polyatomic anion
• CaCO3
• Calcium Carbonate
• NaOH
• Sodium Hydroxide
Writing Formulas for Ionic Compounds
containing polyatomic ions
• The net charge must be zero for the ions
involved
• Work it the same way as the others
• List the cation and the polyatomic ion
involved with their charges
• If you need more than one polyatomic ion
to balance out the compound you must
place the polyatomic ion in parenthesis
and put the subscript after the parenthesis
Examples
•
•
•
•
•
•
Potassium Carbonate
K2CO3
Calcium Hydroxide
Ca(OH)2
Copper (II) Sulfate
CuSO4