Lesson 2: Ionic and Molecular Compounds (2023)

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Table of contents

  • 1. Ionic and Molecular Compounds
  • 2. Intramolecular Bonding in Ionic Compounds
  • 3. Naming Ionic Compounds
  • 4. Naming Molecular Compounds
  • 5. Acids and Bases
  • 6. Self-Check Assessment

1. Ionic and Molecular Compounds

Ionic compounds are defined as being compounds where two or more ions are held next to each other by one of the ions has a positive charge, called a cation, and others have a negative charge called an anion. Cations are usually metal atoms and anions are either non-metals or polyatomic ions.

Ionic compounds have high melting and boiling points and are very hard and very brittle. This is due to the strong bond formed between positive and negative ions. It takes a lot of energy to break these charges apart from each other. Ionic compounds conduct electricity when they dissolve in water.

Water and diamonds- totally different materials. However, they have at least one thing in common. The atoms in these two materials are held together by the type of bond: covalent bonds. These bonds consist of electron shared between two or more atoms. Unlike ionic bonds, where electrons are either lost or gained by an atom to form charged ions, electrons in covalent compounds are shared between the two atoms.

Ionic compounds are formed when metal atoms lose one or more of their electrons to non-metal atoms. The resulting cations and anions are electrostatically attracted to each other. The molecular compound is, on the other hand, formed when the atoms of non-metals share their valence electrons in such a way that they become more stable.Example: CO, CO 2, H 2O, I 2

Key Concepts

Valence electrons
Ionic compounds
Molecular compounds
Acids and Bases

Lesson 2: Ionic and Molecular Compounds (2)

Learn more go to Textbook p.29-36

Polyatomic Ions

A combination of two or more non-metal atoms that have a net charge not equal to zero. Ex. BaCO3

Ionic Hydrates

A substance contaning loosely bonded water molecules. Ex. BaCl2·2H2O

Binary Ionic Compounds

A compound that contains only two kinds of monoatamic ions. Ex. MgBr2

Multi-Valent Metals

The ability of an atom to exist as ions with differnt charges. Ex. UO3, UO2

(Video) Naming Ionic and Molecular Compounds | How to Pass Chemistry

2. Intramolecular Bonding in Ionic Compounds

Electronegativity(EN) is a value that describes the relative attraction of an element to electrons. When two elements form a bond, the electronegativity values for each will indicate how ionic or covalent the bond will be. The larger the difference in EN, the more the intramolecular bond will be.

Valence electrons (ve) are electrons in the highest or outermost, the energy level of the atom. These electrons are the ones that involve in a chemical reaction.

Ionic bondingis found between metals and nonmetals. In general, metals have low EN whereas non-metals have high EN values. When forming an ionic bond, metals lose one or more of their valence electrons. The resulting positively charged cation will have the same electron configuration as the nearest noble gas has.

Na-e---> Na+has the same number of ve as Ne(10).
Cl+e- --> Cl_ has gained one electron to have the same ve as Ar to become more stable. The ionic bond that for between a Na and Cl ions is due to an attraction between opposite charges.

Lesson 2: Ionic and Molecular Compounds (3)

The intramolecular forces within the crystal lattices of ionic solids are the electrostatic attractions between oppositely charged ions.

Ionic compounds consist of ions held together by strong ionic bonding forming a lattice structure. A significant amount of energy is needed to split the lattice. Therefore, ionic compounds have high melting points, are solid at room temperature.

Most ionic compounds dissociate in water due to water molecule's partially positive and negative ends. These opposite ends will be attracted to cations and anions to break the bond. This process will require energy to break bonds.

When the energy released, as the ionic bond breaks, is greater than the energy used to break apart an ionic solid into individual ions, the ionic solid will dissolve in water. Otherwise, it will be insoluble in water.

Ionic compounds react as individual ions. In crystalline form, ionic compounds don't react easily. In an aqueous state, the ionic compound exists as individual ions. Therefore, ionic compounds dissolved in water react more easily than solid ionic compounds.

(Video) Chemistry Lesson: Identifying Ionic vs. Molecular Compounds

3. Naming Ionic Compounds

Multivalent Metals: Transition metals show more than one charge. For example, iron shows charges of 3+ and 2+. When it reacts with a nonmetal such as oxygen, it can form two compounds, Fe2O3 or FeO
a) Stock System(IUPAC system):
Name the metal followed by the size of the charge on the metal followed by the name of the nonmetal.

Fe2O3: iron (III) oxide (red as iron three oxide).
FeO: Iron (II) oxide.
b) Classical System: Latin naming system in which the ion with the grater charge receives an -ic ending, the smaller charge has an -ous ending.
Ex Fe2O3: ferric oxide
FeO: ferrous oxide
Cu2O: copper (I) oxide
CoN: cobalt (III) nitride
PtCl2: platinum (II) chloride

Polyatomic ions stay together in most chemical reactions and are treated in the same way that individual ions are treated when making an ionic compound. Most polyatomic ions are negatively charged but for ammonium. Most names for most of the complexion end in 'ate.
Lithium carbonate:
Li+ CO32- = Li2CO3

Nickel (II) hydrogen carbonate:
Ni2+ HCO3- = Ni(HCO3)2

Ammonium: NH4
Borate: BO3-
Chlorate: ClO3-
dihydrogen phosphate: H2PO4-

Your textbook and data booklet will have the most common polyatomic ions so, no need to memorize them.

Compounds with endings other than -ate
Many compounds can be formed by adding oxygen or hydrogen or by taking away oxygen.
chlorate- ClO3-
perchlorate: ClO4-
chlorite: ClO2-
hypochlorite: ClO-

Diatomic Molecules:
All group 17 elements plus oxygen, nitrogen and hydrogen are diatomic. Their formulas as follows:

F2, Cl2, Br2, I2, At2, N2, O2, H2
There are two polyatomic molecules; sulfur (S8) and phosphorus (P4).

There are some molecules have become known by common names.
ozone: O3
ammonia: NH3
glucose: C6H12O6

(Video) How To Name Ionic Compounds With Transition Metals

4. Naming Molecular Compounds

Binary molecular compounds are named using a system of prefixes which indicate the number of first atoms in the compound. The second atom in the formula gets an -ide ending. The prefix mono is used on the second atom only.


Ex. CCl4: carbon tetrachloride
As2O3: diarsenic trioxide
H2O: dihydrogen monoxide (water)

Non-binary molecular compounds, mostly organic, has a different system of nomenclature.

  • Write out the symbol of the elements in the compound.
  • The first element keeps its name, the second element ends with -ide.
    Ex. NF3: Nitrogen trifluoride

Molecular compounds are composed of non-metals. The atoms within molecules are held together by covalent bonds where atoms share electrons.

The chemical formula for a molecular compound represents the actual number of atoms that form the molecule. For instance, CO2 contains 1 atom of carbon and 2 atoms of oxygen. A covalent on is the attraction of two nuclei for a pair or pairs electrons that they share.
If one pair of election is shared, a single covalent bond is formed. If two pairs of electrons are shared, then a double covalent bond is formed.

Lesson 2: Ionic and Molecular Compounds (4)

5. Acids and Bases


Empirically, acids are aqueous molecular compounds of hydrogen that form electrically conductive solutions. Acids;

  • turn blue litmus paper red
  • react with most metals (Zn and Mg) to produce H2(g) and neutralize bases
  • taste sour

Acids are named in several different ways based on anion endings (-ide, -ate, -ite).

FormulaTheoretical Ionic NameTraditional Name
HClhydrogen chloridehydrochloric acid
H2SO4hydrogen sulfatesulfuric acid
HNO2hydrogen nitritenitrous acid

IUPAC updates suggest that acids be named simply by putting the word 'aqueous' in front of the theoretical ionic name.

FormulaTheoretical Ionic nameUPACTraditional name
HClOhydrogen hypochloriteaqueous hydrogen hypochloritehypochlorous acid
HClhydrogen chlorideaqueous hydrogen chloridehydrochloric acid


Empirically, bases are aqueous ionic hydroxides that form electrically conductive solutions and turn red litmus paper blue.Bases;

  • turn red litmus paper blue
  • taste bitter and feel slippery
  • neutralize acids

Bases are present in the form of alkali metal or alkaline-earth hydroxides. They are named in a very similar way to ionic compounds. Study the following examples.
Ca(OH)2: calcium hydroxide
NaOH: sodium hydroxide
KOH: potassium hydroxide
Bases are present in the form of transition metal hydroxides, the name will use different suffixes since transition metal has two oxidation states. The state with the lower number is given an -ous, the state with the greater number is given -ic suffix.

(Video) CHEM104_Chapter 6 Ionic and Molecular Compounds Part 1

FormulaClassis NameUPAC
CuOHCuprous hydroxideCopper (I) hydroxide
Cu(OH)2Cupric hydroxideCopper(II) hydroxide

Be sure to study textbook p. 34-35

6. Self-Check Assessment

SC1. Ionic Compound: Write the chemical formulas: Potassium iodide, Sodium fluoride, Sodium bicarbonate, Sodium carbonate, Calcium carbonate, Aluminum hydroxide, Magnesium hydroxide, Sodium hydroxide, Potassium phosphate, Magnesium sulfate

Lesson 2: Ionic and Molecular Compounds (5)

SC2. Transition Ionic Compound: Write formulas: Iron (III) chloride, Iron (II) oxide, Iron (III) oxide, Mercury (I) oxide, Mercury (II) oxide, Copper (II) phosphate, Tin (IV) Fluoride, Gallium (III) nitride

Lesson 2: Ionic and Molecular Compounds (6)

SC3. Molecular compounds: Write the common names: SO2, SO3, NO2, N2O4, BCl3, PF5, IF7, Cl2O6

Lesson 2: Ionic and Molecular Compounds (7)

SC4. Study formulas and names of the most common acids and bases.

(Video) CHEM 104 Lecture - Chapter 6 - Ionic and Molecular Compounds Part 1

Lesson 2: Ionic and Molecular Compounds (8)


1. Introduction to Ionic Bonding and Covalent Bonding
(The Organic Chemistry Tutor)
2. Elements, Atoms, Molecules, Ions, Ionic and Molecular Compounds, Cations vs Anions, Chemistry
(The Organic Chemistry Tutor)
3. Ionic vs. Molecular
(Tyler DeWitt)
4. Chapter 2 The Chemical Level of Organization
(AnatomyGMC- Making Anatomy & Physiology Easy)
5. Chapter 2 Ionic Bonds
6. Chapter 2 - Ionic & Covalent bonds
(Stephanie Dufort)
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