Chemical Bonding
Objectives
 Define the key terms
 Distinguish between ionic and molecular
compounds
 Define cation and anion and relate them to
metal and nonmetal
 Distinguish among chemical formulas,
molecular formulas, and formula units
 Use experimental data to show that a
compound obeys the law of definite
proportions
Key Terms
 Monatomic – consist of a single atom
In nature, only the noble gases tend to exist
as isolated atoms.
 Molecule – two or more atoms; smallest
electrically neutral unit of a substance that
still has the properties of that substance
 Molecular compound – compounds
composed of molecular units
The Noble Gases
 Helium – less dense than air; often used to
inflate balloons
 Passing an electric current through a noble
gas produces neon lights:
Neon (orange-red)
Helium (yellowish)
Argon (lavender)
Krypton (whitish)
Xenon (blue)
Molecules
 Diatomic – consist of two atoms
O2 (oxygen) and carbon monoxide (CO)
 Triatomic – consist of three atoms
O3 (ozone) and water (H2O)
Properties of Molecular Compounds
 Low melting and boiling points
 Exist as gases or liquids at room
temperature
 Composed of atoms of two or more
nonmetals
 Proteins and hormones in the body
Ions
 Ion – an atom or group of atoms that has a
positive or negative charge
Formed when an atom or group of atoms
loses or gains electrons
Two Types:
1. Anion – negative charge
2. Cation – positive charge (Circle the top
of the t in the word cation and it looks
like a positive sign.)
Cation
Charge
Anion
Positive
Negative
(Circle the top of
the “t” - it’s a +)
Metal/Nonmetal Metal (Cation
Nonmetal
and Metal both
have a “t” as the
3rd letter of the
word)
Name
Same as
element
Ends in “ide”
Ionic Compounds
 Contain both cations and anions
 Electrically neutral because the total positive
charge of the cations is equal to the total negative
charge of the anions
 Properties:
1. Exist as solid crystals at room
temperature
2. Have relatively high melting points
3. Composed of a metallic element
combined with a nonmetallic element
 Salts in body fluids
Examples




Atoms
Molecules
Cations
Anions
Ne
CH4
Ca2+
F-
He
O2
Na+
O2-
C
H2O
Fe3+
Cl-
 Cations lose electrons and thus gain a
positive charge
 Anions gain electrons and thus gain a
negative charge
Key Terms
 Chemical formula – shows kinds and
numbers of atoms in the smallest
representative unit of the substance
Two Types:
1. Molecular formula – shows kinds and
numbers of atoms present in a molecule of a
compound
2. Formula unit – smallest whole number
ratio of ions in the compound
Examples of Formula Units




NaCl (one Na+ to one Cl-)
MgCl2 (one Mg2+ to two Cl-)
What is the ratio of AlCl3?
1:3
Law of Definite Proportions
 In samples of any chemical compound, the
masses of the elements are always in the
same proportions
 Describes the composition of one compound
 Consistent with Dalton’s atomic theory: If
atoms combine in simple whole-number
ratios, their proportions by mass must
always be the same
Law of Multiple Proportions
 Whenever two elements form more than one
compound, the different masses of one
element that combine with the same mass
of the other element are in the ratio of small
whole numbers.
 Compares the compositions of two different
compounds containing the same elements
Objectives
 Know key terms
 Use the periodic table to determine the
charge on an ion
 Determine the names and formulas of the
most common polyatomic ions
Key Terms
 Monatomic ion – ions consisting of only one
atom
 Polyatomic ions – tightly bound groups of
atoms that behave as a unit and carry a
charge
Ionic Charges of Monatomic Ions
 Metallic elements tend to lose electrons to
form cations
 Group 1A: 1+ Charge
 Group 2A: 2+ Charge
 Group 3A: 3+ Charge
Note: Aluminum is the only common Group
3A metal.
Charges of Group A Nonmetals
 Subtract the group number from 8
 Nonmetals tend to gain electrons and form
anions
 Group 5A: 3- Charge
Note: The three nonmetals are N, P, and Bi.
 Group 6A: 2- Charge
 Group 7A: 1- Charge
 The majority of elements in groups 14 (4A)
and 18 (0) usually do not form ions.
 The elements in Group 18 rarely form
compounds
 Ordinarily, the two nonmetals in Group 14,
carbon and silicon, are found in molecular
compounds.
Summary of Ionic Charges








Group 1A: 1+ Charge
Group 2A: 2+ Charge
Group 3A: 3+ Charge
Group 4A: none (generally)
Note: Cations of tin and lead have more than one
ionic charge.
Group 5A: 3Group 6A: 2Group 7A: 1Group 0 : none
Cations of Transition Metals
 Many have more than one common ionic
charge
 Example: Fe2+ and Fe3+
 Two methods of naming such cations:
1. Stock system: A Roman numeral in
parenthesis indicates the numerical value of
the charge; there is no space between the
element name and the first parenthesis
Examples: iron(II) ion and iron(III) ion
 2. Root word with different suffixes
(Older method and less preferred
because it does not give the charge)
Example: Ferrum is Latin for iron. Use
ferr as root word and ous (smaller) or ic
(larger)
Fe2+ ferrous ion
Fe3+ ferric ion
 A few transition metals have only one ionic
charge:
 Silver: Ag+
 Cadmium and Zinc: Cd2+ and Zn2+
 Note: Many transition metal compounds are
used as pigments.
Polyatomic Ions
 Grouped by charge
 Most names end in ite or ate
Exceptions:
1. Ammonium cation (NH4+)
2. Cyanide anion (CN-)
3. Hydroxide anion (OH-)
 ite ending indicates one less oxygen atom
than the ate ending
Examples
SO32-
ite
sulfite
SO42-
ate
sulfate
NO2-
nitrite
NO3-
nitrate
ClO2-
chlorite
ClO3-
chlorate
Formulas beginning with Hydrogen
 Imagine the H to represent a hydrogen ion
(H+) combined with another polyatomic ion
 Example: HCO3A combination of H+ and CO32Hydrogen carbonate
Note that the charge on the ion
(HCO3- ) is the algebraic sum of the ionic
charges.
Facts to Know
 The hydrogen carbonate anion, hydrogen
phosphate anion and the dihydrogen
phosphate anion are all essential
components of living systems
 The cyanide ion is extremely poisonous to
living systems because it blocks a cell’s
means of producing energy.
 Most laundry and household bleaches
contain the hypochlorite anion.