Lecture 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

Molecular View of Electrolytes and Nonelectrolytes

A pictures showing electrolytes dissociated into ions in water allowing the solution to conduct electricity while nonelectrolytes do not dissociate nor do they allow the solution to conduct electricity.

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 View of Ionic Compounds

An image showing salt in its solid, crystalline form and salt dissociated in water.

Molecular Compounds

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

An image showing crystalline salt along with a molecule of carbon dioxide and a molecule of oxygen.

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

A image of the outline of the Periodic Table with monatomic ions indicated.

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 – \( \chem{NH_4^+} \)

A table of some of the polyatomic ions.

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.

An example of various ionic compounds.

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)

Summary of Main Group Metals

The outline of the Periodic Table with some cation charges overlayed.

How to finish naming ionic compounds

Naming nonmetals
- Monatomic anions
  1. Name according to the periodic table
  2. Drop the ending
  3. Add an –ide
- Polyatomic anions
  - Name according to the Polyatomic Ion Chart (Table 3.4)

Summary of Naming with Transition Metals

A flow chart of naming ionic compounds.

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

Summary of Naming Molecular Compounds

A flow chart of naming molecular compounds.

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: \[ \chem{NaOH(s) \xrightarrow{H_2O} Na^+(aq) + OH^-(aq)} \]

A picture showing dissolving hydrogen chloride gas into water to make hydrochloric acid.

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 1^st 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 (2^nd 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.

Summary of Naming Acids

A flow chart of naming acids.

Summary of Naming Compounds

A flow chart of naming compounds.

A General Summary of Naming Compounds

Type of Compound	Naming
Ionic	Cation named first followed by anion
Molecular	1^st atom in formula (the element farther down or to the left in the periodic table) named 1^st 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.

Lecture 3 Chemical Compounds