Chemical Bonding

1
Chemical Bonding

• Compounds are formed from chemically bound atoms
  or ions.
• Bonding involves only the valence electrons.

2
Chemical Bonding

• Ionic Compounds
• Ionic Radii
• Lattice Energy
• Molecular Compounds
• Covalent bonds
• Bond Order
• Bond Strength
• Lewis Structures

3
Lewis Symbols

• Lewis symbols show the valence electrons as dots
  arranged around the atomic symbol.
• hydrogen
• sodium
• chlorine

4
The Octet Rule

• Atoms tend to gain, lose, or share electrons
  until they have eight valence electrons.

5
Ionic and Molecular Compounds

• Formation of sodium chloride

• Formation of hydrogen chloride

A metal and a nonmetal transfer electrons to form
an ionic compound. Two nonmetals share electrons
to form a molecular compound.
6
Ionic Compounds

• Ionic compounds consist of a lattice of positive
  and negative ions.

7
Ionic Bonds

• An ionic bond is simply the electrostatic
  attraction between opposite charges.

Q2
Ions with charges Q1 and Q2
Q1
The potential energy is given by
8
Ionic Sizes
9
The Lattice Energy

• The lattice energy is the enthalpy change
  required to separate one mole of an ionic
  compound into its ions
• NaCl(s) Na(g) Cl-(g) DH 788 kJ
• Lattice energy increases with increasing ionic
  charges and decreasing ionic sizes.
• KCl(s) K(g) Cl-(g) DH 701
  kJ
• MgCl2(s) Mg2(g) 2 Cl?(g) DH 3795 kJ

10
The Born-Haber Cycle

• The Lattice energy can be calculated with Hesss
  law and the following steps

11
Estimating Lattice Energy

• Arrange with increasing lattice energy
• KCl
• NaF
• MgO
• KBr
• NaCl

701 kJ
910 kJ
3795 kJ
671 kJ
788 kJ
12
Molecular Compounds

• The simplest molecule is H2

The pair of shared electrons constitutes a
covalent bond.
13
Lewis Structures

• Covalent bonding in a molecule is repre-sented
  by a Lewis structure.
• A valid Lewis structure should have an octet for
  each atom except hydrogen.

H2
Cl2
14
Lewis Structures

• Draw Lewis structures for

H F
HF



H2O
NH3
CH4
15
Double and Triple Bonds

• Atoms can share four electrons to form a double
  bond or six electrons to form a triple bond.

O2
N2

• The number of electron pairs is the
• bond order.

16
Electronegativity

• Polarity refers to a separation of positive and
  negative charge. In a nonpolar bond, the bonding
  electrons are shared equally

• In a polar bond, electrons are shared unequally
  because of the difference in Zeff.

17
Electronegativity

• Electronegativity refers to the ability of an
  atom in a molecule to attract shared electrons.
• The Pauling scale of electro- n
  egativity

18
Bond Polarity

• A polar bond can be pictured using partial
  charges

?
??
?? 0.9
2.1
3.0
Electronegativity Difference
Bond Type
0 - 0.5
Nonpolar
0.5 - 2.0
Polar
2.0 ?
Ionic
19
Drawing Lewis Structures

• Sum the valence electrons from all atoms. Add
  one for each negative charge and subtract one for
  each positive charge.
• Draw a skeleton structure with atoms attached by
  single bonds.
• Complete the octets of atoms bound to the central
  atom.
• Place extra electrons on the central atom.
• If the central atom doesnt have an octet, try
  forming multiple bonds.

20
Drawing Lewis Structures



COCl2
24 ves








14 ves
HOCl



?





26 ves
ClO3?






CH3OH
14 ves