Transcript Bond Energies part I

Bond Energies
Types of Chemical Bonds
Chapter 8
Bond Energy
• The strength of the
interaction between
atoms can be
measured by the
amount of energy it
takes to break that
bond.
• Atoms form
ions.
• Ions are
attracted to
oppositely
charged
ions.
• Cations and
anions form
ionic
compounds
Ionic Bonds
Ionic Bonding
• Metals and non
metals form ionic
bonds.
• The degree of ionic
bonding depends on
the nature of the
elements in the
compound.
• Ionic compounds are
often called salts.
Coulomb’s Law
• The energy of an
interaction between a
pair of ions can be
calculated.
• k= 2.31 x 10-19 Jnm
Why do ions form?
• The ion pair in a
compound has
lower energy that
the separated ions.
• What is the energy
of NaCl when the
distance between
the nuclei is 2.76 A
or 0.276 nm?
Answer:
• E=(2.31 x 10-19 Jnm)[(+1)(-1)/(0.276 nm)2]
• = -3.03 x 10-18 J
• Coulomb’s Law may also be used to find
the Energy of the repulsion between two
like charged ions.
Covalent Bonding
• What about atoms
with like charges?
• When two H’s are
brought together, they
actually repulse.
• Under what
conditions will they
bond?
Covalent Bonds
• When they are too
close the repulsive
force of the nuclei
increases the energy.
• When they are too far
apart the energy is
zero.
• At the bond length,
the energy is lowest
and bonding occurs.
Covalent bonding
• When two or more elements share electrons.
• When the electrons are shared equally, it is non
polar covalent.
Polar covalent bonding
• When there is an unequal sharing of electron in
a covalent bond.
• Due to the relative electronegativity of the
elements.
Electronegativity
Polar molecules
• When there is an
unequal sharing of
electrons, partial
charges form on the
compound.
• If that compound may
align in an electric
field, it is polar.
Polar molecules
Not in magnetic field & in magnetic field
What makes a molecule polar?
• Unequal sharing of electrons is due to differences
in electronegativity.
Relative polarities
• Order the following bonds according to
their polarity.
• H-H; O-H; Cl-H; S-H & F-H
• Answer:
• H-H < S-H < Cl-H < O-H< F-H
• 2.1-2.1; 2.5-2.1, 3.0-2.1, 3.5-2.1, 4.0-2.1
• 0
0.4
0.9
1.4 1.9
• Covalent  Polar Covalent Bond