The Chemical Bond
Ionic and Covalent Bonds
Mr. Nelson
Chemistry
Ionic Compounds Overview
 Bonds formed between a metal and a
nonmetal
 Metals form positive ions called cations
 Trick to remember: “ca+ion”
 Non-metals form negative ions called
anions
 Ionic bonds are formed by a transfer of
electrons
Properties of Ionic Compounds
 Ionic compounds dissociate (or break apart) in liquids
 Example: Table salt in water
 Ionic compounds conduct electricity
 If something conducts electricity, then ions/charges
must be able to move
 Solid ionic compounds are rigid, not allowing charges to
move
 Two conditions allow ionic compounds to conduct
electricity:
 Molten (or liquid)
 Dissolved in solution
 Example: Li-ion batteries
Properties of Ionic Compounds
 Ionic compounds tend to have high melting
points
 This is due to the high strength of the ionic
bonds
 Stronger bonds need more energy to break apart!
Formation of Ionic Compounds
 Ionic bonds follow the Octet Rule
 Octet rule – Each element tends to form
compounds based on the easiest way to gain
8 valence electrons
 Example: Na and Cl
 Sometimes combinations are not an easy oneto-one ratio!
 Example: Ca and Cl
Formation of Ionic Compounds
 Examples
 Mg and O
 K and S
 Practice
 Ba and N
 Li and P
Formation of Ionic Compounds
 Transition metal ionic compounds
 All form positive ions (cations), but can form
multiple ions
 Example: FeCl2 and FeCl3
Covalent Compounds Overview
 Covalent bonds are made between
nonmetals only
 Does NOT depend on charges!!
 Covalent bonds will share electrons as
both elements need to gain electrons to
obtain full outer shell (8 valence
electrons)
Properties of Covalent Compounds
 Forms longer bonds because bonds are weaker
than ionic bonds
 Energy is lowered when atoms form a covalent
bond
 This is the main driving force behind their
formation
 There is a balance between their attractive
and repulsive forces
 Potential energy curve for H2 bond
Potential
Energy
Bond Length
Two Types of Covalent Bonds
 Polar covalent bonds are covalent bonds
where electrons are shared unequally
between the atoms
 Non-polar covalent bonds are covalent
bonds where electrons are shared
equally between the atoms
Polarity
 Polarity depends on differences in
electronegativity
 The greater the difference in
electronegativity, the more polar the bond is
 Example: Cl2 and HF
 The more polar the bond, the stronger the
bond
 Polar covalent bonds have stronger bonds
than non-polar bonds
 Stronger bonds give higher boiling points
(just like ionic compounds)
The Chemical Bond Overview
 In order of increasing bond strength:
 In order of increasing bond length:
Naming Ionic Compounds
 Simple Naming Rules
 Identify the compound as Ionic
(Metal and a non-metal)
 Determine charges for each ion
 Overall charge of compound must
be zero
 General formula for names:
 Cation + Anion Root-ide
Examples
 Calcium fluoride
 Calcium phosphide
 Magnesium nitride
 Potassium oxide
Examples
 LiCl2
 SrBr2
 BaI2
Transition Metal Compounds
 Since transition metals form multiple ions, roman
numerals denote charge
Examples
 iron (III) chloride
 copper (II) oxide
 iron (III) oxide
 silver (I) sulfide
Polyatomic Ion Compounds
 Some elements are considered as a
charged group of two or more atoms.
They are considered as a single ion
called a polyatomic ion.
 You will not need to memorize these,
only recognize it when you see them
Examples
 Aluminum chromate
 Potassium hydroxide
 Sodium thiosulfate
 Calcium acetate