Study Notes: Ionic and Molecular Compounds (Chapter 6, GOB Chemistry)

Ionic and Molecular Compounds

Molecular Compounds: Sharing Electrons

Molecular compounds are formed when atoms of two or more nonmetals share electrons, resulting in covalent bonds. The sharing of valence electrons allows nonmetal atoms to achieve stability, and the resulting molecule is a discrete group of atoms in a definite proportion.

• Covalent Bond: A chemical bond formed by the sharing of electrons between nonmetal atoms.

• Molecule: A group of atoms bonded together in a specific ratio.

• Example: Water (H2O) is a molecular compound formed by sharing electrons between hydrogen and oxygen.

Naming Molecular Compounds

The names of molecular compounds require prefixes because several different compounds can be formed from the same two nonmetals. The naming process follows specific rules:

• First Nonmetal: Named by its element name.

• Second Nonmetal: Named using the first syllable of the element name followed by ide.

• Prefixes: Indicate the number of atoms of each element (see Table 6.10 below).

Prefixes Used in Naming Molecular Compounds

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

Examples of Naming Molecular Compounds

• NCl3: Nitrogen trichloride (no prefix for one nitrogen, 'tri' for three chlorines).

• B2O3: Diboron trioxide ('di' for two borons, 'tri' for three oxygens).

• NO: Nitrogen monoxide (the prefix 'mono' is often omitted for the first element).

Common Molecular Compounds

Name	Formula
Carbon dioxide	CO2
Carbon monoxide	CO
Dinitrogen oxide	N2O
Water	H2O
Ammonia	NH3
Methane	CH4
Sulfur trioxide	SO3
Dinitrogen tetroxide	N2O4
Dichlorine heptoxide	Cl2O7

Writing Formulas from Names

To write the formula from the name of a molecular compound, use the symbol for each element and a subscript if a prefix indicates two or more atoms.

• Example: Diphosphorus pentoxide: 'di' = 2 phosphorus atoms, 'penta' = 5 oxygen atoms. Formula: P2O5.

Distinguishing Ionic and Covalent Compounds

A compound is usually ionic if the first element in the formula or name is a metal or a polyatomic ion. It is covalent if the first element is a nonmetal.

• Ionic Compound Example: Potassium oxide (K is a metal).

• Covalent Compound Example: Dinitrogen oxide (N is a nonmetal).

Flowchart for Naming Compounds

To name chemical compounds, first determine if it is molecular (two nonmetals) or ionic (a metal and a nonmetal). For molecular compounds, use prefixes and end the second element with ide. For ionic compounds, name the cation (metal or ammonium) and the anion (monatomic or polyatomic).

• Molecular: Prefix + element name (first nonmetal), prefix + element name + 'ide' (second nonmetal).

• Ionic: Name of metal or ammonium (with Roman numeral if necessary), name of anion (ending in 'ide' for monatomic, or polyatomic ion name).

Learning Checks and Solutions

• Example 1: Name B2O3: Diboron trioxide.

• Example 2: Write the formula for diphosphorus pentoxide: P2O5.

• Example 3: Identify compound as ionic or covalent and give its correct name:

  • Sulfur trioxide: Covalent

  • Barium chloride: Ionic

  • Ammonium phosphite: Ionic

  • Dinitrogen tetroxide: Covalent

Summary Table: Ionic vs. Covalent Compounds

Type	Elements Involved	Naming Rule
Ionic	Metal + Nonmetal or Polyatomic Ion	Name cation, then anion (use Roman numeral if needed)
Covalent	Nonmetal + Nonmetal	Use prefixes, end second element with 'ide'

*Additional info: The textbook cover is included as it directly identifies the source and context for the chapter and study notes.*