IONIC COMPOUNDS

Chapter 8

Forming Chemical BondsSection 8.1

The force that holds two atoms together is called a chemical bond.

Chemical bonds may form by the attraction between a positive nucleus and negative electrons or the attraction between a positive ion and a negative ion

Review… Valence electrons are the electrons in the

outermost energy level. These same electrons are involved in the formation of chemical bonds between two atoms

Electron-Dot Structures

Especially useful when illustrating formation of chemical bonds!!

From Chapter 6… Ionization energy refers to how easily

an atom loses an electron. Noble gases, having high ionization

energies, show a general lack of chemical reactivity

The difference in reactivity is directly related to the valence electrons

Elements tend to react to acquire the stable electron structure of a noble

gas (V.E. 8)

Formation of Positive Ions

A positive ion forms when an atom loses one or more valence electrons in order to attain a noble gas configuration

Positively charged ion is called a

cation

Transition Metals

When forming positive ions, transition metals commonly lose their valence electrons, forming 2+ ions. However, it is also possible for d

electrons to be lost

A useful rule of thumb for these metals is that they form ions with a 2+ or 3+ charge.

Formation of Negative Ions

Nonmetals have a great attraction for electrons and form stable outer electron configuration by gaining electrons

Negatively charged ion is called an

anion

Checkpoint Why do ions form? Describe the formation of positive and

negative ions. Predict the change that must occur to

achieve noble gas stability• Nitrogen• Sulfur• Barium• Lithium

Answers Atoms gain stability by losing or gaining

electrons Positive ions form when atoms lose valence

electrons Negative ions form when valence electrons are

added to an atom Nitrogen- gain 3 electrons (N3-) Sulfur- gain 2 electrons (S2-) Barium- lose 2 electrons (Ba2+) Lithium- lose 1 electron (Li1+)

CW

P.214 #1-5 P.236 #47-50, 60-66

The Formation and Nature of Ionic Bonds (Section 8.2) The electrostatic force

that holds oppositely charged particles together in an ionic compound is referred to as an ionic bond

Ionic bonds form between cations (+) and anions (-)

Binary compounds contain two different elements Metallic cation Nonmetallic anion

Electrons gained = electrons lost

OVERALL CHARGE OF THE COMPOUND FORMED MUST BE ZERO!!!

Properties of Ionic Compounds1. High Melting and boiling points

(indicating strong bond strength)

2. Most are crystalline solids at room temperature

3. ions in a regular, geometric pattern (crystal lattice)

4. hard, brittle5. conduct electricity when

molten or dissolved in water (aka electrolyte)

Homework

P.220 #12-18 P.236 #53,67-73

Names and Formulas for Ionic Compounds

(Very Important!) Section 8.3

Terms to be familiar with: Formula Unit- the simplest ratio of the

ions represented in an ionic compound Monatomic Ion- a one-atom ion (Mg2+ or

Br1-) Oxidation Number- the charge of the

monatomic ion Polyatomic Ion- ions made up of more

than one atom (i.e. Nitrate= NO2-)

Predicting ionic ratios

Based on charge ratios (“formula units” – simplest ratio of the ions)

Cations first, anions second For example

Na 1+ and Cl 1- ; therefore, will combine 1:1 NaCl “sodium chloride”

Na 1+ and S 2-; therefore, will combine 2:1 Na2S “sodium sulfide”

Be 2+ and N 3-; therefore, will combine 3:2 Be3N2 “beryllium nitride”

Write the correct formula for the ionic compound composed of the following pairs of ions

1. Potassium and iodine2. Magnesium and chlorine3. Aluminum and bromide4. Cesium and nitride

Answers

1. Potassium and iodineK+1 and I-1 KI (1:1 ratio)

2. Magnesium and chlorine Mg+2 and Cl-1 MgCl2 (1:2 ratio)

3. Aluminum and bromide Al+3 and Br-1 AlBr3 (1:3 ratio)

4. Cesium and nitride Cs+1 and N-3 Cs3N (3:1 ratio)

Compounds Containing Polyatomic Ions

The charge given to a polyatomic ion applies to the entire group of atoms

The polyatomic ion acts as an individual ion NEVER CHANGE THE SUBSCRIPTS

WITHIN THE ION If more than one polyatomic ion is needed,

place parentheses around the ion and write the appropriate subscript outside the parentheses.

Practice Problems

Calcium and Nitrate Aluminum and Hydroxide Barium and Sulfate Sodium and Phosphate Potassium and Sulfate

Naming Ionic Compounds

Oxyanion- a polyatomic ion composed of an element, usually a nonmetal, bonded to one or more oxygen atoms An ion with more oxygen atoms is named

using the root of the nonmetal plus the suffix –ate (ex. NO3

- nitrate) An ion with fewer oxygen atoms is

named using the root of the nonmetal plus the suffix –ite (ex. NO2

- nitrite )

Chlorine’s 4 Oxyanions

ClO4- perchlorate (most oxygen's)

ClO3- chlorate (one less oxygen)

ClO2- chlorite (two fewer oxygen's)

ClO- hypochlorite (three fewer oxygen's)

Naming Ionic Compounds

1. Name the cation (+) first and the anion (-) second.

2. Monatomic cations use the element name.

3. Monatomic anions take their element name plus the suffix –ide.

4. Transition metals (d-block cations) often have more than one oxidation number. The oxidation number is written as a

Roman numeral in parentheses after the name of the cation

5. If the compound contains a polyatomic ion, simply name the ion.

Practice problems

1. NaBr2. CaCl23. KOH4. Cu(NO3)2

5. Ag2CrO4

Cation + Anion

1. NaBr sodium bromide2. CaCl2 calcium chloride

3. KOH potassium hydroxide4. Cu(NO3)2 copper (II) nitrate

5. Ag2CrO4 silver chromate

Writing a Chemical Formula from the Name

Step 1: Write the element symbol(s) for name of the ion(s).

Step 2: Write the charge of the ion(s). Step 3: If the total charge equals zero,

you are done. If the total charge does not equal zero, you must change the subscripts so that the total charge equals zero (‘drop-n-cross’).

Section Review

AnionCation

Oxide Chloride Sulfate Phosphate

Potassium

Barium

Aluminum

Ammonium

Answers AnionCation

Oxide Chloride Sulfate Phosphate

Potassium K2O KCl K2SO4 K3PO4

Barium BaO BaCl2 BaSO4 Ba3(PO4)2

Aluminum Al2O3 AlCl3 Al2(SO4)3 AlPO4

Ammonium (NH4)2O NH4Cl (NH4)2SO4 (NH4)3PO4

Homework

P.227 #35-36,38-39 P.237 #74-79

Metallic Bonds and Properties of Metals (Section 8.4)

Although metals do not bond ionically, they often form lattices in the solid state.

Electron sea model- all the metal atoms in a metallic solid contribute their valence electrons to form a “sea” of electrons

The electrons present in the outer energy levels of the bonding metallic ions are not held by any specific atom and can move easily from one atom to the next. (Delocalized electrons)

A metallic bond is the attraction of a metallic cation for delocalized electrons

Metal Alloys A mixture of elements that has metallic

properties Substitutional- atoms of the original metallic

solid are replaced by other metal atoms of similar size Brass, pewter, 10-carat gold, and sterling silver

Interstitial- formed when small holes in a metallic crystal are filled with smaller atoms Carbon steel

Homework

P.237 #80-82,84