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Molecular vs Ionic Compounds

Name a molecular compound given its formula and write formulas given compound names

Lesson Objectives

This study guide reviews:

  • • Ionic vs molecular compounds
  • • Properties of each type
  • • Naming rules for molecular compounds
  • • Common prefixes and their meanings
  • • Worked multiple-choice and true/false examples

1. Ionic Compounds

Key Characteristics

  • • Made of positive (cations) and negative (anions) ions
  • • Electrons are transferred, not shared
  • • Exist as extended crystal lattices, not individual molecules
  • • Represented by empirical formulas

Example Question:

One of the following statements about ionic compounds is not correct.

  1. 1. ionic compounds are represented by empirical formulas
  2. 2. ionic compounds take the form of individual molecules
  3. 3. ionic compounds exist in extended arrays
  4. 4. ionic compounds are made up of alternating positive and negative ions

✅ Correct answer: 2

Ionic compounds do not exist as individual molecules.

2. Molecular (Covalent) Compounds

Key Characteristics

  • • Formed between nonmetals
  • • Electrons are shared
  • • Exist as individual molecules
  • • Molecules in a pure sample are identical

Example Question:

One of the following statements about molecular compounds is not true

  1. 1. molecular compounds share valence electrons
  2. 2. molecular compounds form bonds between pairs of atoms
  3. 3. molecular compounds lose electrons to nonmetal atoms
  4. 4. all the molecules in a sample of a given molecular compound are identical

✅ Correct answer: 3

Losing electrons describes ionic, not molecular, bonding.

3. True / False Concept Checks

Carbon dioxide consists of a central carbon atom bonded to two oxygen atoms.

✅ True

Water is an ionic compound.

❌ False

Water is a molecular (covalent) compound.

4. Binary Molecular Compounds

Definition

  • • Binary = two different elements
  • • Molecular = nonmetals bonded covalently

Example Question:

Binary molecular compounds are usually composed of

  1. 1. two metals
  2. 2. a metal and a non-metal
  3. 3. two nonmetals
  4. 4. three or more different elements

✅ Correct answer: 3

5. Prefixes Used in Molecular Naming

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

Example Question:

The prefix _____ could be used to indicate a molecule with eight carbon atoms

  1. 1. penta
  2. 2. hexa
  3. 3. hepta
  4. 4. octa

✅ Correct answer: 4

6. Interpreting Names with Prefixes

Example Question:

The compound ethane pentabromide would contain _____ bromine atoms.

  1. 1. five
  2. 2. three
  3. 3. seven
  4. 4. four

✅ Correct answer: 1

7. Writing Molecular Formulas (Order Matters)

Element Order Rules

  • • The less electronegative element is written first
  • • The more electronegative element is written second

Example Question:

The nonmetal ___ would follow S when writing binary compound formulas

  1. 1. Cl
  2. 2. I
  3. 3. H
  4. 4. P

✅ Correct answer: 1

8. Naming Molecular Compounds (True / False)

P2O5 is named phosphorus pentaoxide.

❌ False

Correct name: diphosphorus pentoxide

N and O can combine with each other in a variety of ratios.

✅ True

CO would be named carbon monoxide.

✅ True

CCl4 is the formula for carbon trichloride.

❌ False

Correct name: carbon tetrachloride

9. Naming Compounds from Formulas

NO →

nitrogen monoxide

N2O5 →

dinitrogen pentoxide

H2O →

dihydrogen monoxide
(technical name)

C2F6 →

dicarbon hexafluoride

SiO2 →

silicon dioxide

NH3 →

nitrogen trihydride
(technical name)

10. Writing Formulas from Names

Example Question 1:

The formula for xenon hexachloride is

  1. 1. XeCl4
  2. 2. XeCl6
  3. 3. XeCl8
  4. 4. XeCl5

✅ Correct answer: 2

Example Question 2:

The formula for carbon tetrachloride is

  1. 1. CCl
  2. 2. CCl2
  3. 3. CCl3
  4. 4. CCl4

✅ Correct answer: 4

Example Question 3:

Boron trihydride has the following formula

  1. 1. BH3
  2. 2. B2H3
  3. 3. B2H6
  4. 4. B3H6

✅ Correct answer: 1

11. Final True / False Practice

The formula for dinitrogen tetroxide is N2O2.

❌ False

Correct: N2O4

The formula for sulfur trioxide is SO3.

✅ True

The formula for selenium tetrahydride is SeH5.

❌ False

Correct: SeH4

12. Writing Formulas (Practice Set)

bromochloride →

BrCl

arsenic triiodide →

AsI3

disilicon tetroxide →

Si2O4

tellurium difluoride →

TeF2

diboron hexahydride →

B2H6

triphosphorus octoxide →

P3O8

Key Takeaways

  • • Molecular compounds involve shared electrons between nonmetals
  • • Prefixes tell you exact numbers of atoms (mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-)
  • • Ionic compounds do not form molecules—they exist as crystal lattices
  • • Always check element order and prefix meaning when writing formulas

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