1. 1/30/13
CHM 101
Ch 3: Ionic Compounds
Key Vocabulary Terms
•Ion – a charged atom
•Cation – a positively (+)
charged ion
•Anion – a negatively (-)
charged ion
2. Ionic Compounds
Noble gases typically do not form ions or bonds.
Why?
Octet Rule
An octet is 8 valence electrons, and is associated with the stability of the noble
gases.
(Exception: He is stable with 2 valence electrons (duet).)
valence electrons
He 1s2 2
Ne 1s2 2s2 2p6 8
Ar 1s2 2s2 2p6 3s2 3p6 8
Kr 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 8
3. Chemical Bonding
Octet Rule
Atoms form octets to become more stable.
• They do this by losing, gaining, or sharing valence electrons.
• In the process, they form ionic bonds or covalent bonds.
4. Chemical Bonding
Ionic compound – compound consisting of negatively and positively
charged ions. Electrons are not shared between the ions. They are
transferred from atoms of one element to atoms of another element.
NaCl, MgBr2, KI, etc. Ionic compounds are
usually composed of a
metal and a nonmetal
Covalent compound – compound consisting of atoms of different
elements that share electrons in covalent bonds.
H2O, CCl4, C6H12O6, etc. Covalent compounds
are usually composed of
only nonmetals
5. Chemical Bonding
Identify the following compounds as ionic or covalent:
a. Na2S Ionic
b. CuCl2 Ionic
c. CH4 Covalent
d. PCl3 Covalent
6. Ionic Compounds
Formation of a Sodium Ion, Na+
With the loss of its valence electron,
the sodium ion has a +1 charge.
Sodium atom Sodium ion
11p+ 11p+
11e- 10e-
0 1+
1s2 2s2 2p6 3s1 1s2 2s2 2p6
Sodium achieves an octet by losing its one valence electron.
7. Ionic Compounds
Formation of Magnesium Ion, Mg2+
With the loss of two valence
electrons, magnesium forms a
positive ion with a +2 charge.
Mg atom Mg2+ ion
12p+ 12p+
12e- 10e-
0 2+
1s2 2s2 2p6 3s2 1s2 2s2 2p6
Magnesium achieves an octet by losing its two valence electrons.
8. Ionic Compounds
Metals Form Positive Ions
Metals form cations (positive ions) by losing one or
more of their valence electrons to have the electron
configuration of the nearest noble gas.
The ions have fewer electrons than protons.
Group 1A metals → ion 1+
Group 2A metals → ion 2+
Group 3A metals → ion 3+
9. Ionic Compounds
Formation of a Chloride Ion, Cl–
By gaining one electron, the
chloride ion has a -1 charge.
Chlorine atom Chloride ion
17p+ 17p+
17e- 18e-
0 1–
1s2 2s2 2p6 3s2 3p5 1s2 2s2 2p6 3s2 3p6
Chlorine achieves an octet by adding an electron to its valence electrons.
10. Ionic Compounds
Formation of Negative Ions
Nonmetals form anions (negative ions) by gaining
one or more electrons to have the electron
configuration of the nearest noble gas.
The ions formed have more electrons than protons.
Group 6A nonmetals → ion 2−
Group 7A nonmetals → ion −
14. Ionic Compounds
Other ions – You must know these charges.
Some metals have more than one charge when they form cations.
15.
16. Ionic Compounds
Ionic compounds consist of positive and negative ions (very often metal
cation and nonmetal anion.
Sodium chloride (NaCl) or “table salt” is an example of an ionic
compound.
17. Ionic Compounds
An ionic formula has charge balance.
total positive charge = total negative charge
The symbol of the cation is written first followed by the symbol of the
anion. How many anions do you need for each cation?
In sodium chloride, we need one
chloride ion for each sodium ion.
Formula:
NaCl
We use subscripts to describe
the number of ions.
No subscript means “one”.
18. Ionic Compounds
Charge Balance In MgCl2
In magnesium chloride, we need
two chloride ions for each
magnesium ion.
We use subscripts to describe
the number of ions.
Formula:
MgCl2
19. Ionic Compounds
Writing Ionic Formulas
Let’s make an ionic compound from these ions: Na+ and N3−.
For each nitride ion, N3-, how many sodium ions, Na+, do we need?
How do we write the formula?
Practice: Write a formula for an ionic compound made of Ba 2+ and Cl-.
Practice: Write a formula for an ionic compound made of Pb4+ and O2-.
20. Ionic Compounds
Rules for Naming Ionic Compounds
1. The name of the cation comes first, then the name of the anion.
2. For metals that only form 1 cation, the cation name is the same as the metal
name.
Ca2+ - calcium ion
3. For metals that can form more than 1 cation, the charge is indicated with
Roman numerals.
Fe2+ - iron (II)
Fe3+ - iron (III)
4. Monatomic anions are named by adding –ide to the root name.
O2− - oxide
F− - fluoride
21. Ionic Compounds
Rules for Naming Ionic Compounds
Metal cation name is same as Nonmetal anion name changes
element name element ending to –ide.
23. Ionic Compounds
Guide to Writing Formulas from the Name
1. Identify the cation and the anion.
2. Determine their charges (the Roman numeral gives the charge.)
3. Balance the charges.
4. Write the formula with the cation first, use subscripts to indicate
the number of each ion.
Write the formula for lead (II) fluoride.
24. Ionic Compounds
Polyatomic Ions
A polyatomic ion is a molecular
unit of atoms with an overall
ionic charge.
**You MUST know these
names and formulas!**
25. Ionic Compounds
Naming Compounds with Polyatomic Ions
The cation is named first
followed by the name of the
polyatomic ion.
NaNO3 sodium nitrate
K2SO4 ?
Fe(HCO3)3 ?
(NH4)3PO4 ?
26. Ionic Compounds
Writing Formulas with Polyatomic Ions
The formula of an ionic compound containing a polyatomic ion must
have a charge balance that equals zero (0).
Na+ and NO3− : NaNO3
If there are two or more polyatomic ions they must be in parentheses.
Use subscripts to indicate how many are present.
Mg2+ and 2NO3− : Mg(NO3)2
subscript 2 for charge balance
Practice: Write the formula for chromium (II) hydroxide.
27. Ionic Compounds
Use the table below to quiz yourself. Use the formula, write the name.
Use the name, write the formula.
28. Ionic Compounds
Properties of Ionic Compounds
H2 O
In solid ionic compounds, When dissolved in water, ions
the ions are held rigidly in dissociate, dispersing (+) and (–)
place. charged ions in solution.
KBr (s) K+ (aq) + Br- (aq)
Ionic compounds are electrolytes – substances that conduct electricity
when dissolved in water.
