Ionic Bonding and Ionic Compounds

1
Chapter 15

• Ionic Bonding and Ionic Compounds

2
Electron Configuration in Ionic Bonding

• Valence Electrons
• The electrons in the highest occupied energy
  level of an elements atoms.
• The of valence electrons determines chemical
  properties
• Elements within each group have the same of
  valence electrons
• See table 15.1 p. 414
• Electron dot structures are diagrams that show
  valence electrons as dots.

3
Electron Dot Structures
4
Electron Configuration in Ionic Bonding (cont)

• Electron Configurations for Cations
• Octet rule In forming compounds, atoms tend to
  achieve the electron configuration of a noble gas
  (an octet is a set of eight).
• The most common cations are those produced by the
  loss of valence electrons from metal atoms.
• Some transition metals are exceptions to the
  octet rule.

5
Electron Configuration in Ionic Bonding (cont)

• Electron Configurations for Anions
• Nonmetallic atoms have relatively full valence
  shells and they achieve the octet more easily by
  gaining electrons.
• Halide ions are the ions produced when the
  halogens gain electrons. All halogen ions have
  seven valence electrons and need to gain only one
  electron to achieve the electron configuration of
  a noble gas.

6
Ionic Bonds

• Anions cations have opposite charges and they
  attract one another by electrostatic forces.
• The forces of attraction that bind these
  oppositely charged ions are called ionic bonds.
• The total of positive charges must equal the
  total negative charges
• The maximum charge an ion is likely to have is 3.
• Sample problem 15-1 p. 421.

7
Properties of Ionic Compounds

• At room temperature, most ionic compounds are
  crystalline solids.
• The coordination number of an ion is the number
  of ions of opposite charge that surround the ion
  in a crystal.
• Ionic compounds are salts.

8
Bonding in Metals

• Metals often form lattices in the solid state.
• In such a lattice, 8-12 other metal atoms closely
  surround each metal atom.
• Within the crowded lattice, the outer energy
  levels of the metal atoms overlap.
• This is a unique arrangement that is described by
  the electron sea model.
• The electron sea model proposes that all the
  metal atoms in a metallic solid contribute their
  valence electrons to form a sea of electrons.
  This sea of electrons surrounds the metal cations
  in the lattice.

9
Bonding in Metals

• The electrons can move easily from one atom to
  the next.
• Because they are free to move, they are often
  referred to as delocalized electrons.
• When the atoms outer electrons move freely
  throughout the solid, a metallic cation is
  formed.
• A metallic bond is the attraction of a metallic
  cation for delocalized electrons.

10
Electron Sea Model
11
B. Free electrons can move rapidly in response to
electric fields, hence metals are a good
conductor of electricity. C. Free electrons can
transmit kinetic energy rapidly, hence metals are
good conductors of heat. D. The layers of atoms
in metal are hard to pull apart because of the
electrons holding them together, hence metals are
tough. But individual atoms are not held to any
other specific atoms, hence atoms slip easily
past one another. Thus metals are ductile.
Metallic Bonding is the basis of our industrial
civilization.
12
Properties of Metals

• Metals have moderately high melting points
  boiling points.
• Metals are malleable which means they can be
  hammered into sheets they are ductile which
  means they can be drawn into wires.
• Metals are generally durable.
• The delocalized electrons move heat from one
  place to another much more quickly than the
  electrons in a material that does not contain
  mobile electrons.
• Mobile electrons easily move as part of an
  electric current when an electric potential is
  applied to a metal.
• As the number of delocalized electrons increases,
  so do the properties of hardness strength.

13
Metal Alloys

• An alloy is a mixture of elements that has
  metallic properties.
• Due to the nature of metallic bonds, it is
  relatively easy to introduce other elements into
  the metal crystal.
• Stainless steel, brass, and cast iron
• Properties of alloys
• They differ somewhat from the properties of the
  elements they contain.
• Steel has some properties of iron but has
  additional properties, such as increased strength.

14
Types of Alloys

• Substitutional alloys
• Some of the atoms in the original metallic solid
  are replaced by other metals of similar atomic
  size.
• Interstitial alloys
• Small holes (interstices) in a metallic crystal
  are filled with smaller atoms.

15
(No Transcript)
16
Commercial Alloys

• Alnico magnets
• 50 Fe, 20 Al, 20 Ni, 10 Co
• Brass plumbing, hardware, lighting
• 67-90 Cu, 10-33 Zn
• Bronze bearings, bells, medals
• 7095 Cu, 1-25 Zn, 1-18 Sn
• Cast iron casting, cookware
• 96-97 Fe, 3 4 C
• Gold, 10K jewelry
• 42 Au, 12-20 Ag, 37.46 Cu
• Lead shot shotgun shells
• 99.8 Pb, .2 As
• Pewter tableware
• 70-95 Sn, 5-15 Sb, 0-15 Pb
• Stainless steel instruments, sinks, cookware
• 73-79 Fe, 14-18 Cr, 7-9 Ni
• Sterling silver tableware, jewelry
• 92.5 Ag, 7.5 Cu

17
Everyday Chemistry

• Costume jewelry, particularly pieces made in
  developing countries, could have high levels of
  lead.
• When lead gets wet, a certain amount of it
  dissolves, becoming lead (II) ions. Inside the
  body, these ions can replace calcium ions and
  cause learning disabilities, coma or death.
• Leaded gasoline was phased out in the mid 1970s
  and as a result lead levels in Americans blood
  dropped.

18
(No Transcript)