
# Chapter 3 Chemical Compounds

Shaun Williams, PhD

## Ionic and Molecular Compounds

### Electrolytes and Nonelectrolytes

• Electrolytes
• substances that release ions when dissolved in water
• This process is also called dissociation or ionization
• conduct electricity
• Nonelectrolytes
• substances that do NOT dissociate in water
• do NOT conduct electricity
• Example: methanol

### Strong and Weak Electrolytes

• Strong electrolytes
• dissociate completely into ions in water
• conduct electricity well
• Examples: NaCl and HCl
• Weak electrolytes
• do not dissociate completely into ions in water
• do not conduct electricity well
• Example: acetic acid

### Ionic Compounds

• Are composed of a metal cation and a nonmetal anion
• Metals cations are
• positively charged ions
• Nonmetals anions are
• negatively charged ions
• Their cations and anions exist in proportions that give electrical neutrality
• These ions are arranged in a crystal lattice
• Also called salts
• Are one of the major categories of chemical compounds

### Molecular Compounds

• Are composed of 2 or more nonmetals
• Have no overall charge
• Are the other major category of chemical compounds

### Ionic and Molecular Compound Properties

Properties of Ionic and Molecular Compounds
Ionic Compounds Molecular Compounds
Crystalline solid Gas, liquid, or solid
Hard, brittle solid Soft solid
Very high melting point Low melting point
Very high boiling point Low boiling point
High density Low density
Strong electrolyte in aqueous solution Weak or nonelectrolyte in aqueous solution
Electrical conductivity is good when compound is molten Electrical conductivity is poor in pure form

## Monatomic and Polyatomic Ions

### Monoatomic Ions

• Are ions of a single atom
• Many are shown below on Figure 3.12 and Table 3.2
• Most main-group elements tend to form their ion charge based on how far away their group is from the noble gases
• Transition metals tend to form multiple charges

### Polyatomic Ions

• An ion containing 2 or more atoms, usually of more than one element
• The most common are oxoanions, anions that contain oxygen attached to another element.
• Many are shown below on Figure 3.17 and Table 3.4
• One polyatomic cation – $$\chem{NH_4^+}$$

### Important Polyatomic Anions

Ions with a $$1-$$ charge Ions with a $$2-$$ charge
Nitrate $$\chem{NO_3^-}$$ Chromate $$\chem{CrO_4^{2-}}$$
Nitrite $$\chem{NO_2^-}$$ Dichromate $$\chem{Cr_2O_7^{2-}}$$
Bicarbonate $$\chem{HCO_3^-}$$ Sulfate $$\chem{SO_4^{2-}}$$
Perchlorate $$\chem{ClO_4^-}$$ Sulfite $$\chem{SO_3^{2-}}$$
Chlorate $$\chem{ClO_3^-}$$ Carbonate $$\chem{CO_3^{2-}}$$
Chlorite $$\chem{ClO_2^-}$$ Oxalate $$\chem{C_2O_4^{2-}}$$
Hypochlorite $$\chem{ClO^-}$$ Peroxide $$\chem{O_2^{2-}}$$
Cyanide $$\chem{CN^-}$$ Ions with a $$3-$$ charge
Hydroxide $$\chem{OH^-}$$ Phosphate $$\chem{PO_4^{3-}}$$
Acetate $$\chem{C_2H_3O_2^-}$$ Phosphite $$\chem{PO_3^{3-}}$$
Permanganate $$\chem{MnO_4^-}$$ Borate $$\chem{BO_3^{2-}}$$

## Formulas for Ionic Compounds

### Writing Formulas for Ionic Compounds

• When writing a formula for an ionic compound, the sum of the positive charges must equal the sum of the negative charges. $\text{Total positive charge} + \text{total negative charge} = \text{zero net charge}$
• The crystal structures or lattices are composed of repeating units called formula units.

## Naming Ionic Compounds

### How to name ionic compounds

• Naming metals
• Monatomic cations are named according to the periodic table
• Transition metals (and Sn and Pb) require a Roman numeral in parenthesis to designate their charge (using the Stock System)

### How to finish naming ionic compounds

• Naming nonmetals
• Monatomic anions
1. Name according to the periodic table
2. Drop the ending
• Polyatomic anions
• Name according to the Polyatomic Ion Chart (Table 3.4)

## Naming and Writing Formulas for Molecular Compounds

### Naming Molecular Compounds

• We will name binary molecular compounds
• Binary Compounds
• A compound containing atoms or ions of only two elements
• To name molecular compounds, we:
• Name the leftmost element as we would a main-group metal – according to the periodic table.
• Name the rightmost element as we would a monatomic anion – drop the ending of the name (from the periodic table) and add an “-ide”.
• Use Greek prefixes to denote the number of atoms of each element.

### Common Greek Prefixes

Prefix Name Prefix Name
mono- 1 hexa- 6
di- 2 hepta- 7
tri- 3 octa- 8
tetra- 4 nona- 9
penta- 5 deca- 10

## Acids and Bases

### What are acids and bases?

• Acids
• Are substances that when dissolved in water provide hydrogen ions ($$\chem{H^+}$$)
• An example of the dissociation (or ionization) of an acid: $\chem{HCl(aq) \xrightarrow{H_2O} H^+ (aq) + Cl^- (aq)}$
• Bases
• Are substances that react with acids in aqueous solution to form water
• An example of the ionization of a base: $\chem{NaOH(s) \xrightarrow{H_2O} Na^+(aq) + OH^-(aq)}$

### Names of Some Common Acids

Formula Name Formula Name
$$\chem{HF(aq)}$$ Hydrofluoric acid $$\chem{H_2SO_4(aq)}$$ Sulfuric acid
$$\chem{HCl(aq)}$$ Hydrochloric acid $$\chem{H_2SO_3(aq)}$$ Sulfurous acid
$$\chem{HI(aq)}$$ Hydroiodic acid $$\chem{HClO_4(aq)}$$ Perchloric acid
$$\chem{H_2S(aq)}$$ Hydrosulfuric acid $$\chem{HClO_3(aq)}$$ Chloric acid
$$\chem{H_2CO_3(aq)}$$ Carbonic acid $$\chem{HClO_2(aq)}$$ Chlorous acid
$$\chem{HNO_3(aq)}$$ Nitric acid $$\chem{HClO(aq)}$$ Hypochlorous acid

### Naming Acids

• Since most acids have a hydrogen as their 1st element in the molecular formula, the acids are named according to the anion, not the cation ($$\chem{H^+}$$).
• Binary acids are named as hydro- followed by the root of the element (2nd element or anion) name with an –ic suffix and the word acid placed at the end of the name.
• Acids containing polyatomic ions (as the anion) are named by taking the root of the polyatomic ion name, replacing –ate with –ic or replacing –ite with –ous and adding the word acid at the end.

### A General Summary of Naming Compounds

Type of Compound Naming
Ionic Cation named first followed by anion
Molecular 1st atom in formula (the element farther down or to the left in the periodic table) named 1st with the second element named as if it were an anion. Greek prefixes are used to designate the number of atoms in a molecule.
Acids Binary acids are named as hydro- followed by the root of the element name with an –ic suffix and the word acid placed at the end of the name. Acids containing polyatomic ions are named by taking the root of the polyatomic ion name, replacing –ate with –ic or replacing –ite with –ous and adding the word acid at the end.

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