1. Ch. 6.3
Ions
Ionic Bonding

2. POINT > Review ion basics
POINT > Describe ionic bonds
POINT > Distinguish between molecular formulas and formula units
POINT > Describe the arrangement of ions in crystals
POINT > Describe the properties of ionic compounds
POINT > Define polyatomic ions

3. POINT > Review ion basics
Valence electrons are electrons in the highest occupied energy level of an atom
Number of valence e- is the same as Group number for main group elements (Groups – Subtract 10)

4. POINT > Review ion basicsCa Ne
Valence electrons determine chemical properties of the element
Valence e- are the only electrons directly involved in chemical bonds
Valence e- are shown by Electron Dot (Lewis) Structure diagrams

5. POINT > Review ion basics

6. Gilbert Lewis (1875 – 1946) POINT > Review ion basics
Used stability of noble gases to explain why atoms form certain kind of ions & molecules
Called explanation the Octet Rule

7. POINT > Review ion basics
Octet rule: When forming compounds, atoms tend to achieve the electron configuration of a noble gas
Configurations will end in ns2np6

8. POINT > Review ion basics
Metals tend to lose valence e- to form positive charged cations
Nonmetals tend to gain valence e- to form negative charged anions

9. POINT > Review ion basics
Cation name matches that of the atom (a lithium atom forms a lithium cation)
Cations are usually metals (atoms that have 1-3 valence electrons)

10. POINT > Review ion basicsMg
2e-
Mg2+ +

11. POINT > Review ion basics
Transition metals are less predictable: charges produced may vary
Ex. Iron (Fe) often forms 2+ or 3+ cations
Ex. Copper (Cu) forms 1+ or 2+ cations

12. POINT > Review ion basics
The anion name differs from that of its atom, typically ending in –ide
Ex. chlorine atoms form chloride anions
sulfur atoms form sulfide anions
oxygen atoms form oxide anions, etc

13. POINT > Review ion basics+

14. WB CHECK:
Which would form an anion?
strontium
calcium
aluminum
sulfur
chromium

15. WB CHECK:
Which would form a cation?
lithium
potassium
aluminum
sulfur
oxygen
a-c
d-e

16. POINT > Describe ionic bonds
Ionic compounds are composed of metal cations & nonmetal anions
Ionic compounds are electrically neutral as a whole, even though they are made of ions
Positive charges must equal negative charges

17. POINT > Describe ionic bonds
Ionic bonds result from electrostatic forces between ions of opposite charge The ions that form follow the octet rule

18. POINT > Distinguish between molecular formulas and formula units
A chemical formula shows the numbers of atoms in the smallest representative unit of a substance
Ex. H2O, C6H12O6, NaCl, MgBr2
For covalent compounds the unit is a molecule and the chemical formula is a molecular formula

19. POINT > Distinguish between molecular formulas and formula units
Ionic compounds do not exist as discrete units Exist as a crystal lattice—not as discrete molecules

20. POINT > Distinguish between molecular formulas and formula units
The formula unit is the lowest whole-number ratio of ions in an ionic compound (ex NaCl, CaCl2)
For ionic compounds, chemical formulas are written as formula units because there is no discrete unit (the arrangement just repeats indefinitely)

21. WB CHECK:
Which of these is a molecular formula?
MgF2
SrO
CF4
Li2S
all of the above

22. WB CHECK:
Which of these is a formula unit?
CO2
CaCl2
CF4
SO2
all of the above

23. WB CHECK:
Which of these is a chemical formula?
CO2
CaCl2
CF4
SO2
all of the above

25. WB CHECK:
The atoms in an ionic compound are held together by
a) shared electrons
b) differences in electronegativity
c) electrostatic attraction
d) electron affinity
e) magic

26. POINT > Describe the arrangement of ions in crystals
Most ionic compounds are crystalline solids at room temp
Coordination number is the number of oppositely-charged ions that surround an ion of interest
Each type of ion has its own number

27. POINT > Describe the arrangement of ions in crystals
Coordination Number:
Chloride is 6
Oxide is 3
Chloride is 8
Titanium is 6
Sodium is 6
Cesium is 8

28. POINT > Describe the properties of ionic compounds
Ionic compounds have high melting & boiling points (compared to molecular compounds)
Due to strong attractions between charged ions
Good conductors when molten or dissolved in H2O
Brittle (easily broken) because planes repel each other when dislocated

29. POINT > Define polyatomic ions
A polyatomic ion: a charged group of covalently bonded atoms; e.g. NH4+ or CO32-
Note the Lewis structures: brackets, charge shown, and number of electrons

30. Homework
Read pages F.A. page 184 #1-4