Ch 3: Ionic CompoundsKey Vocabulary Terms

•Ion – a charged atom

•Cation – a positively (+) charged ion

•Anion – a negatively (-) charged ion

1/30/13 CHM 101

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 electronsHe 1s2 2

Ne 1s2 2s2 2p6 8

Ar 1s2 2s2 2p6 3s2 3p6 8

Kr 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 8

Octet Rule

Ionic Compounds

Noble gases typically do not form ions or bonds.

Why?

Chemical Bonding

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.

Octet Rule

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

Chemical Bonding

Identify the following compounds as ionic or covalent:

a. Na2S

b. CuCl2

c. CH4

d. PCl3

Chemical Bonding

Ionic

Ionic

Covalent

Covalent

Formation of a Sodium Ion, Na+

Sodium achieves an octet by losing its one valence electron.

1s2 2s2 2p6 3s1 1s2 2s2 2p6

With the loss of its valence electron,the sodium ion has a +1 charge.

Sodium atom Sodium ion 11p+ 11p+

11e- 10e-

0 1+

Ionic Compounds

Formation of Magnesium Ion, Mg2+

Magnesium achieves an octet by losing its two valence electrons.

1s2 2s2 2p6 3s2 1s2 2s2 2p6

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+

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+

Ionic Compounds

Formation of a Chloride Ion, Cl–

Chlorine achieves an octet by adding an electron to its valence electrons.

1s2 2s2 2p6 3s2 3p5

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 3p6

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

Ionic Compounds

Electronegativity

What property determines which atoms will lose electrons and which atoms will gain electrons?

ELECTRONEGATIVITY!

Electronegativity

• Electronegativity is a measure of an atom’s tendency to attract electrons

Increasing

Increasing

Ionic Compounds

Main Group Ions – You must know these charges.

Ionic Compounds

Other ions – You must know these charges.

Some metals have more than one charge when they form cations.

Sodium chloride (NaCl) or “table salt” is an example of an ionic compound.

Ionic compounds consist of positive and negative ions (very often metal cation and nonmetal anion.

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”.

Ionic Compounds

Charge Balance In MgCl2

In magnesium chloride, we need two chloride ions for each magnesium ion.

Formula: MgCl2

We use subscripts to describe the number of ions.

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 Ba2+ and Cl-.

Practice: Write a formula for an ionic compound made of Pb4+ and O2-.

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 - oxideF - fluoride

Ionic Compounds

Metal cation name is same as element name

Nonmetal anion name changes element ending to –ide.

Rules for Naming Ionic Compounds

Ionic Compounds

Write names for the following ionic compounds:

a. MgS

b. FeCl2

c. SnF2

d. Cr2O3

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.

Ionic Compounds

Write the formula for lead (II) fluoride.

A polyatomic ion is a molecular unit of atoms with an overall ionic charge.

Polyatomic Ions

Ionic Compounds

**You MUST know these names and formulas!**

The cation is named first followed by the name of the polyatomic ion.

NaNO3 sodium nitrate

K2SO4 ?

Fe(HCO3)3 ?

(NH4)3PO4 ?

Naming Compounds with Polyatomic Ions

Ionic Compounds

Writing Formulas with Polyatomic Ions

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.

The formula of an ionic compound containing a polyatomic ion must have a charge balance that equals zero (0).

Na+ and NO3− : NaNO3

Ionic Compounds

Use the table below to quiz yourself. Use the formula, write the name. Use the name, write the formula.

Ionic Compounds

Properties of Ionic Compounds

In solid ionic compounds, the ions are held rigidly in place.

H2O

When dissolved in water, ions dissociate, dispersing (+) and (–) charged ions in solution.

KBr (s) K+ (aq) + Br- (aq)

Ionic compounds are electrolytes – substances that conduct electricity when dissolved in water.

Ionic Compounds

No current in distilled water.

Ionic Compounds

No current in solid ionic compound.

Ionic Compounds

Current!!!

Ionic Compounds

Covalent compounds do not dissociate into ions when dissolved in water. Therefore, they are nonelectrolytes.

C6H12O6 (s) C6H12O6 (aq)

Molecular vs. Ionic Compounds

Ionic Compounds