SCH4U – UNIT 1
STRUCTURE AND
PROPERTIES
CHAPTER 4 – CHEMICAL BONDING
Activity
• With a partner discuss everything you remember about
chemical bonding
• Eg. Types of bonds? why? What happens?
4.1 Types of Chemical Bonds
• What are the two main types of chemical bonds?
• Ionic: chemical bond between oppositely charged ions
• Electrostatic attraction
• Covalent: a chemical bond in which atoms share bonding electrons
• Bonding Electron Pair: electron pair that is involved in bonding
• Bond type depends on the attraction for electrons of the
atoms involved
• i.e. electronegativity
Ionic Compounds
How do these work?
Metal + Non-Metal  Metal+ + Non-MetalLow IE
Low EA
High IE
High EA
Isoelectronic with noble gases
Opposites attract in no particular direction, considered nondirectional
Ions cling together in clusters known as crystals
• Get a lattice structure
• Lattice energy: energy change when one mole of an ionic
substance is formed from its gaseous ions
• Depends on:
• Charge on the ions
• Size of the ions
Ionic Compounds and Bonding
• Properties – WHY?
• Do not conduct electric current in the solid state
• Conduct electric current in the liquid state
• When soluble in water, form good electrolyte
• Relatively high MP and B
• Brittle, easily broken under stress
Covalent Bonds
Balance of attractive and repulsive forces
What are the forces acting here?
Octet Rule
• Atoms share electrons so that they are surrounded by 8
electorns
• # bonds = 8 - # valence electorn
• Example: Carbon, Oxygen, Nitrogen
• Two covalent bonds = double bond
• Three covalent bonds = triple bond
Polar Covalent Bonds
• When electrons are shared unevenly
• Example: HF, H2O
Coordinate Covalent Bonds
• Both electrons are contributed by one atom
• Example:
• NH4+
• H 3 O+
• CO
• N 2O
• NHO3
Resonance Structures
• Single bonds are longer than double bonds, which are
longer than triple bonds
• Example: SO3
• Resonance Structure: Electron pair is shared over three
bond evenly
• Delocalized electrons
Less than 8
• BeH2
• BCl3
More than 8
• Octet rule only applies to the first two periods
• After that, can have expanded octets
• Example:
• PF5
• BrF5
• SiF63-
Lewis Structures
• Atoms and ions are stable if they have a full valence shell
• Electrons are most stable when they are pair
• Atoms form chemical bonds to achieve full valence shells
of electrons
• Full valence shell may occur by an exchange or by
sharing electrons
• Sharing – covalent; exchange - ionic