1. Chapter 4
Chemical Bonding:
Ionic Bond Model

2. Sec 4.1 Chemical Bonds Free atoms are generally not encountered
Atoms form molecules and aggregates
Two broad types of compounds, ionic compounds and molecular compounds
Ionic compounds are the subject of Chap 4
Molecular compounds are the subject of Chap 5

3. Sec 4.1 Chemical Bonds
In general ionic compounds share some similar properties:
High melting points (500 – 2000 oC)
Conduct electricity when in liquid or solution form
Solids (often crystals) at room temperature
Made up by ionic bonds
Ionic bond – a chemical bond formed through the transfer of electrons from one atom to another

4. Sec 4.1 Chemical Bonds Fundamentals of chemical bonds
1. Not all electrons in an atom participate in bonding. Generally only the outermost level are available
These electrons are known as valence (Sec 4.2)
2. Certain arrangements of electrons are very stable. This is referred to by the octet rule (Sec 4.3)

5. Sec 4.2 Valence Electrons
Valence shell: the outermost incomplete shell
Valence electron: an electron in the valence shell
For these definitions we generally refer to the main group elements. Transition metals behave differently
For main group elements, valence electrons are always found in the s and p subshells

6. Sec 4.2 Valence Electrons
We write a shorthand called a Lewis Structure to show the symbol and the valence electrons for an element
Lewis Structure is merely the symbol of an element surrounded by dots equal to the number of valence electrons

7. Sec 4.2 Valence Electrons
Figure 4.1 Page 77 Showing Lewis Structures

8. Sec 4.2 Valence Electrons General Patterns and Rules:
Elements in the same group (column) have the same number of valence electrons
The number of valence electrons is the same as the Roman Numeral numbering system
IA has 1, VIIA has 7, etc
The maximum number of valence electrons for any element (with a few exceptions) is eight

9. Sec 4.3 The Octet Rule
Stable, in the context of electrons and atoms, means that the atom does not easily undergo spontaneous change
The most stable configuration of electrons is the noble gas configuration (s and p filled)
For all but He, this is a filled valence shell with 8 electrons (hence octet). He is filled with 2
Octet Rule: in forming compounds, elements gain, lose, or share electrons in order to produce a stable noble gas configuration for all atoms involved

10. Sec 4.4 The Ionic Bond Model
Isotopes – change the neutrons and mass but not the charge for an atom
Ions – an atom with the normal number of protons and neutrons but a change in electrons that changes the charge

11. Sec 4.4 The Ionic Bond Model
Ions have two possibilities, a positive charge or a negative charge
Anion – atom gains electrons, therefore negative charge (example F-1)
Cation – atom loses electrons, therefore positive charge (example Mg+2)
Why not a change of protons for a change in charge?
Disagree with book as far as notation

12. Sec 4.5 Sign and Magnitude of Ions
What determines the normal ion charge for an element?
Elements tend to gain or lose electrons to reach a full valence shell (octet rule)
Many elements have two pathways to reach a full valence shell. Choose the path of less resistance
For example, losing 2 electrons is easier than gaining 6

13. Sec 4.5 Sign and Magnitude of Ions
Metals containing 1-3 valence electrons (Groups IA, IIA, and IIIA) tend to lose electrons (positive charge)
Nonmetals containing 5-7 valance electrons (Groups VA, VIA, and VIIA) tend to gain electrons (negative charge)
Elements in Group IV would be expected to gain or lose 4 but instead these elements form covalent bonds (Chap 5)

14. Sec 4.5 Sign and Magnitude of Ions
Example, predict Oxygen, Phosphorus, Argon, Potassium, Aluminum, Carbon
Transition metals and series elements are harder to predict, some can form several ions with different charges
In general the charges on transition metals will be given or can be determined by context
Iron (II) ion means Fe+2
Iron (III) ion means Fe+3

15. Sec 4.6 Ionic Compound Formation
Elements don’t lose or gain electrons in a vacuum. Where does a lost electron go?
Ionic bonds involve transfer, one element loses an electron and another gains it
Lewis dot structures often make it easy to visualize the electron transfer process
Examples and how to write the compound out

16. Sec 4.7 Chemical Formulas
“Criss-cross” method for balancing ionic compounds
The overall compound should be neutral
Reduce the subscripts to the lowest ratio of whole numbers
Examples: BaI2 (note charges not written)
Fe(III)2O3
MgO (note reduction of ratio)

17. Sec 4.8 Structure of Ionic Compounds
Ionic compounds in a solid state form a lattice of alternating positive and negative ions
Figure 4.4 (a) through (c) Page 85

18. Sec 4.8 Structure of Ionic Compounds
The lattice extends in 3 dimensions so each positive is surrounded by negative and vice versa
Because of the larger structure, the formula generally refers to a formula unit
Formula unit is the smallest ratio neutral unit that repeats itself in the overall compound

19. Sec 4.9 Naming Ionic Compounds
Binary Ionic Compounds contains only two elements, a metal and a nonmetal
The metal always comes first
Named by using the name of the metal element followed by the stem of the nonmetal with the suffix –ide
Fluoride, Oxide, Bromide

20. Sec 4.9 Naming Ionic Compounds
Table of Nonmetal names and ion charges found Table 4.2 page 88
Examples of naming:
Na2S, Al2O3 , CuBr3 , CaCl2
Examples of formulas:
Iron (III) Oxide, Potassium Iodide, Magnesium Sulfide
Fixed Charge aside on page 90 Green

21. Sec 4.9 Naming Ionic Compounds
Figure 4.7 Page Copper (II) oxide is black, whereas copper (I) oxide is reddish brown. Iron (II) chloride is green, whereas iron (III) chloride is bright yellow.

22. Sec 4.10 Polyatomic Ions
Sometimes ions can be formed by several atoms acting together as one unit
Polyatomic ions behave in the same way as monoatomic ions, treat them as a single unit
Polyatomic ions are not molecules
The vast majority of polyatomic ions are negatively charged (exception being NH4+)

23. Sec 4.10 Polyatomic Ions
Table 4.3
Page 91
Common
Polyatomic ions

24. Sec 4.11 Naming Ionic Compounds II
Naming ionic compounds containing polyatomic ions is similar to naming binary ionic compounds
Metal named first, polyatomic ion named second

25. Sec 4.11 Naming Ionic Compounds II
Two things arise when writing chemical formulas
1. You MUST use parentheses when there is more than one polyatomic ion is required
Examples: Fe(OH)3
2. Keep polyatomic units together, even if the same element appears elsewhere in the formula
Examples: NH4NO3

26. Sec 4.11 Summary of Naming
Chemistry at a Glance Page 94

27. Problems Assigned problems pages 95 - 98 4.1, 4.7, 4.8
4.11, 4.13, 4.19, 4.25, 4.27
4.29, 4.33, 4.39, 4.41, 4.43, 4.49
4.55, 4.57, 4.61
Practice Test page 98