Chemical Bonding
Covalent and Ionic Bonding
A Chemical Bond
 A chemical bond is a mutual electrical
attraction between the nuclei and valence
electrons of different atoms that binds the
atoms together.
 Bonds are rarely ever purely ionic or
covalent.
 Electronegativity differences between
bonding elements determine ionic character.
 0  0.3
(Nonpolar covalent)
 0.3 1.7
(Polar covalent)
 1.7  3.3
(Ionic)
Examples
 HCl (3.0 – 2.5) =
 0.5, polar – covalent
 CaCl (3.0 – 1.0) =
 2.0, ionic
 Br-Cl (3.0 – 2.8) =
 0.2, nonpolar – covalent
Covalent Bonding and Molecular
Compounds
 A molecular (molecule-atoms held together
by covalent bonds) compound is a chemical
compound whose simplest units are
molecules.
 The chemical formula of a molecular
compound is referred to as a molecular
formula.
 Covalent bonds result in lower potential
energies from a balance between attractive
and repulsive forces.
Bond Length
 Bond length is the distance between two
bonded atoms at their minimum potential
energy.
 Average bond length results from the balance
between attraction and repulsion in a stable
covalent bond.
 Bond energy is the energy required to break a
chemical bond and form neutral isolated
atoms.
Bond Length vs. Energy
The Octet Rule
 Chemical compounds tend to form so that
each atom, by gaining, losing, or sharing
electrons, has an octet of electrons in its
highest occupied energy level.
 Most main-group elements form covalent
bonds according to the octet rule.
 There are some exceptions, for example,
Boron that has three valence electrons and
tends to bond surrounded by 6 electrons.
Electron-Dot Notation and
Lewis Structures
 Electron-dot notation depicts the valence
electrons surrounding an atom.
 Lewis structures utilizes pairs of dots or
dashes to represent covalent bonds between
atoms.
 Lewis structure
 Structural formula
Lewis Structures
Multiple Bonds
 Double and triple bonds occur when
elements share more than one electron
pair.
 Bonds are generally shorter with higher
energy.
Ionic Bonding and Compounds
 Ionic compounds are composed of positive
and negative ions that are combined so that
the numbers of positive and negative charges
are equal.
 Ions minimize their potential by combining in
an orderly pattern known as the crystal lattice.
Ionic bonding in NaCl
Polyatomic Ions
 A charged group of covalently bonded atoms
is known as a polyatomic ion.
SO3-2
CN-
NO3-
NH4+