Bonding: General Concepts

1
Bonding General Concepts

• Chapter 8

2
Words to know

• chemical bond
• ionic bond
• covalent bond
• metallic bond
• Lewis Symbol
• Octet rule

3
Practice

• Classify the following compounds as ionic or
  covalent. Justify your answer. Which compounds
  contain both types of bonds?
• - KBr - SO2
• - H2SO4 - CH3COOH
• - Na3PO4 - CaCO3

4
Lewis Symbol

• Element symbol with valence electrons written
  around it as dots
• Elements want to gain, lose, or share electrons
  to look like a noble gas (isoelectronic)

5
Place the following chemical species into
isoelectronic groups

• N3-, K, Ca2, O2-, F-, Ne, Br, Kr, Sc3, Na,
  Al3, Se2-, Mg2

6
Ionic Bonding

• electrons are transferred from an atom with low
  electronegativity to one with high EN
• electrostatic attraction between the two
  oppositely charged ions
• arranged in a crystal lattice (lattice energy,
  DHL, is energy required to completely separate
  solid ionic compound into gaseous ions)

7
Lattice Energies?

• Lattice energy increases when the atoms are
  smaller or have a higher charge (exchanging more
  electrons)
• higher lattice energy means the ionic compound is
  more strongly bonded
• high lattice energies also explains why ionic
  compounds are brittle and hard

8
In each of the following pairs of compounds,
identify the one with the higher lattice energy

• KCl, CaS
• LiF, NaCl
• Fe2O3, MnO2
• CaO, CaCl2

9
Ions

• Representative elements follow the hill of
  oxidation numbers when in ionic compounds
• transition metals (including lead tin) are a
  little weird
• Their valence electrons are the highest filled s
  sublevel and occasionally 1 or more of their d
  electrons

10
Transition Metal Ions

• Iron
• Fe Ar 4s23d6
• Fe2 Ar 3d6
• Fe3 Ar 3d5
• Lead
• Pb Xe 6s24f145d106p2
• Pb2 Xe 6s24f145d10
• Pb4 Xe 4f145d10

11
Write the electron configurations for Cr3 and
Sn4
12
Covalent Bonding

• 2 atoms sharing electrons
• Lewis structures show shared and lone pairs of
  electrons
• polar or non-polar determined by difference in EN
  values for the 2 bonding elements
• 0-0.4 NPC
• .4-1.0 PC
• 1.0-2.0 really PC
• gt2.0 ionic

13
Dipoles

• With polar covalent bonds, there is a dipole (one
  end of the bond hogs the shared electrons a
  little more than the other)
• symbolized with d and d- and are not whole
  number charges

14
Drawing Lewis Structures

1. Add up the total valence electrons of all bonding
   atoms
2. Use one pair of electrons to bond each outer atom
   to the central atom (usually the least EN or the
   one present in the least abundance)
3. Complete octets around all of the outer atoms
4. Place any remaining electrons around the central
   atom
5. If there arent enough electrons to give the
   central atom an octet, make multiple bonds

15
Practice

• Write the Lewis structures for each of the
  following compounds
• NO3-
• CO2
• PCl5
• NO3

16
Resonance Structures

• used when 2 Lewis structures are equally good
  representations of the bonds
• actual structure is kind of an average of all the
  possibilities
• examples include ozone nitrate ion

17
Exceptions to Octet Rule

• When there is an odd of electrons, one atom
  will only have 7 electrons around it. (NO, NO2)
• When the compound has a group 2 or 3 element as
  the central atom, the number of electrons around
  the central atom will be twice the group number
• If central element is big, it can have an
  expanded octet (PCl5)

18
Covalent Bond Strength

• Multiple covalent bonds are stronger than single
  covalent bonds (they are also shorter)
• Higher the number of electrons shared, the
  stronger the bond