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Chapter 15 Ionic Bonding and Ionic Compounds

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Title: Chapter 15 Ionic Bonding and Ionic Compounds


1
Chapter 15Ionic Bonding and Ionic Compounds
  • Charles Page High School
  • Dr. Stephen L. Cotton

2
Section 15.1Electron Configuration in Ionic
Bonding
  • OBJECTIVES
  • Use the periodic table to infer the number of
    valence electrons in an atom, and draw its
    electron dot structure.

3
Section 15.1Electron Configuration in Ionic
Bonding
  • OBJECTIVES
  • Describe the formation of cations from metals,
    and of anions from nonmetals.

4
Valence Electrons
  • The electrons responsible for the chemical
    properties of atoms are those in the outer energy
    level.
  • Valence electrons - The s and p electrons in the
    outer energy level
  • the highest occupied energy level
  • Core electrons -those in the energy levels below.

5
Keeping Track of Electrons
  • Atoms in the same column...
  • Have the same outer electron configuration.
  • Have the same valence electrons.
  • Easily found group number on the periodic table
    for representative elem.
  • Group 2A Be, Mg, Ca, etc.
  • 2 valence electrons

6
Electron Dot diagrams
  • A way of keeping track of valence electrons.
  • How to write them?
  • Write the symbol.
  • Put one dot for each valence electron
  • Dont pair up until they have to (Hunds rule)

X
7
The Electron Dot diagram for Nitrogen
  • Nitrogen has 5 valence electrons.
  • First we write the symbol.

N
  • Then add 1 electron at a time to each side.
  • Until they are forced to pair up.

8
Write electron dot diagrams
  • Na
  • Mg
  • C
  • O
  • F
  • Ne
  • V

9
Electron Configurations for Cations
  • Metals lose electrons to attain noble gas
    configuration.
  • They make positive ions (cations)
  • If we look at the electron configuration, it
    makes sense to lose electrons
  • Na 1s22s22p63s1 1 valence electron
  • Na1 1s22s22p6 noble gas configuration

10
Electron Dots For Cations
  • Metals will have few valence electrons (usually 3
    or less)

Ca
11
Electron Dots For Cations
  • Metals will have few valence electrons
  • These will come off

Ca
12
Electron Dots For Cations
  • Metals will have few valence electrons
  • These will come off
  • Forming positive ions

Ca2
Pseudo-noble gas configuration
Now make Sc an ion.
13
Electron Configurations for Anions
  • Nonmetals gain electrons to attain noble gas
    configuration.
  • They make negative ions (anions)
  • Halide ions- ions from chlorine or other halogens
    that gain electrons
  • S 1s22s22p63s23p4 6 valence electrons
  • S2- 1s22s22p63s23p6 noble gas configuration.

14
Electron Dots For Anions
  • Nonmetals will have many valence electrons
    (usually 5 or more)
  • They will gain electrons to fill outer shell.

P
P3-
15
Stable Electron Configurations
  • All atoms react to achieve noble gas
    configuration.
  • Noble gases have 2 s and 6 p electrons.
  • 8 valence electrons .
  • Also called the octet rule.

Ar
16
Section 15.2Ionic Bonds
  • OBJECTIVES
  • List the characteristics of an ionic bond.

17
Section 15.2Ionic Bonds
  • OBJECTIVES
  • Use the characteristics of ionic compounds to
    explain the electrical conductivity of ionic
    compounds when melted and when in aqueous
    solution.

18
Ionic Bonding
  • Anions and cations are held together by opposite
    charges.
  • Ionic compounds are called salts.
  • Simplest ratio is called the formula unit.
  • The bond is formed through the transfer of
    electrons.
  • Electrons are transferred to achieve noble gas
    configuration.

19
Ionic Bonding
Na
Cl
20
Ionic Bonding
Na
Cl-
21
Ionic Bonding
  • All the electrons must be accounted for!

Ca
P
22
Ionic Bonding
Ca
P
23
Ionic Bonding
Ca2
P
24
Ionic Bonding
Ca2
P
Ca
25
Ionic Bonding
Ca2
P 3-
Ca
26
Ionic Bonding
Ca2
P 3-
Ca
P
27
Ionic Bonding
Ca2
P 3-
Ca2
P
28
Ionic Bonding
Ca
Ca2
P 3-
Ca2
P
29
Ionic Bonding
Ca
Ca2
P 3-
Ca2
P
30
Ionic Bonding
Ca2
Ca2
P 3-
Ca2
P 3-
31
Ionic Bonding
Ca3P2
Formula Unit
Sample Problem 15-1, page 421
32
Properties of Ionic Compounds
  • Crystalline structure, usually solids
  • A regular repeating arrangement of ions in the
    solid Fig. 15.9, p.423
  • Ions are strongly bonded together.
  • Structure is rigid.
  • High melting points
  • Coordination number- number of ions of opposite
    charge surrounding it

33
Crystalline structure
34
Do they Conduct?
  • Conducting electricity is allowing charges to
    move.
  • In a solid, the ions are locked in place.
  • Ionic solids are insulators.
  • When melted, the ions can move around.
  • Melted ionic compounds conduct.
  • NaCl must get to about 800 ºC.
  • Dissolved in water they conduct (aqueous)

35
Section 15.3Bonding in Metals
  • OBJECTIVES
  • Use the theory of metallic bonds to explain the
    physical properties of metals.

36
Section 15.3Bonding in Metals
  • OBJECTIVES
  • Describe the arrangements of atoms in some common
    metallic crystal structures.

37
Metallic Bonds
  • How atoms are held together in the solid.
  • Metals hold on to their valence electrons very
    weakly.
  • Think of them as positive ions (cations) floating
    in a sea of electrons Fig. 15.13, p.427

38
Sea of Electrons
  • Electrons are free to move through the solid.
  • Metals conduct electricity.

39
Metals are Malleable
  • Hammered into shape (bend).
  • Also ductile - drawn into wires.
  • Both malleability and ductility explained in
    terms of the mobility of the valence electrons
  • Fig. 15.14, p.427

40
Malleable
41
Malleable
  • Electrons allow atoms to slide by.

42
Ionic solids are brittle
43
Ionic solids are brittle
  • Strong Repulsion breaks crystal apart.

44
Crystalline structure of metal
  • If made of one kind of atom, metals are among the
    simplest crystals
  • Note Fig. 15.16, p.428 for types
  • 1. Body-centered cubic
  • every atom has 8 neighbors
  • Na, K, Fe, Cr, W

45
Crystalline structure of metal
  • 2. Face-centered cubic
  • every atom has 12 neighbors
  • Cu, Ag, Au, Al, Pb
  • 3. Hexagonal close-packed
  • every atom also has 12 neighbors
  • different pattern due to hexagonal
  • Mg, Zn, Cd

46
Alloys
  • We use lots of metals every day, but few are pure
    metals
  • Alloys - mixtures of 2 or more elements, at least
    1 is a metal
  • made by melting a mixture of the ingredients,
    then cooling
  • Brass an alloy of Cu and Zn
  • Bronze Cu and Sn

47
Why use alloys?
  • Properties often superior to element
  • Sterling silver (92.5 Ag, 7.5 Cu) is harder and
    more durable than pure Ag, but still soft enough
    to make jewelry and tableware
  • Steels are very important alloys
  • corrosion resistant, ductility, hardness,
    toughness, cost

48
Why use alloys?
  • Table 15.3, p.429 - common alloys
  • Types? a) substitutional alloy- the atoms in the
    components are about the same size
  • b) interstitial alloy- the atomic sizes quite
    different smaller atoms fit into the spaces
    between larger
  • Amalgam- dental use, contains Hg
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