Section 2.6: Molecular and Ionic Compounds

By Doba Jackson, Ph.D.

Molecules, Ions, and Chemical Bonds

Covalent Bond: A bond that results from the sharing of electrons between atoms.

Ionic Bond: A bond that results from oppositely charged ions that are electrostaticlly attracted to each other.

Definitions of Molecules, Ions, and Chemical Bonds

Ionic Bond: An electrostatic attraction between charged particles. Typically a metal bonded to a nonmetal.

Ion: A charged atom or molecule.

Cation: A positively charged particle. Most cations are metals.

Anion: A negatively charged particle. Nonmetals tend to form anions.

Ions, and Chemical Bonds

In the formation of sodium chloride, one electron is transferred from the sodium atom to a chlorine atom.

Na+1 + Cl-1Na + Cl2

11 protons10 electrons

17 protons18 electrons

11 protons11 electrons

17 protons17 electrons

1

2

Evidence for existence of ions

We can predict many element’s ionic charge based on its location on the

periodic table

Naming Ionic Compounds

+1+2 +3 -3 -2 -1Naming (IUPAC)

Cation Anion

Na+1 Cl-1

Sodium Chloride

Metals tend to form Cations

Nonmetals tend to form Anions

Naming Ionic Compounds

Ionic Compound: A neutral compound in which the total number of positive charges must equal the total number of negative charges.

Some binary Ionic Compounds

Cation – Anion(ide) Cation AnionIonic

Compound

cation anion(ide) C+x A-y CyAx

aluminum sulfide: Al2S3Al+3 S-2

sodium chloride NaClNa+1 Cl-1

magnesium oxide MgOMg+2 O-2

Determine the charge on each ionic compound and name the compound

MgS

BaF2

AlP

Ga2O3

Li2O

Mg3N2

CaS

Fe+3 O-2

Pb+4 O-2

Ni+2 Br-1

Manganese (IV) Oxide

Tungsten (VI) bromide

Mg+2

Ba+2

Al+3

Ga+3

Li+1

Mg+2

Ca+2

Mn+4

W+6

S-2

F-1

P-3

O-2

O-2

N-3

S-2

O-2

Br-1

Magnesium sulfide

Barium flouride

Aluminum Phosphide

Gallium oxideLithium oxide

Magnesium nitride

Calcium sulfide

Iron (III) oxide

Lead (IV) oxide

Nickel Bromide

Fe2O3

PbO2

NiBr2

MnO2

WBr6

Some transition metals have more than one stable charge

What happens when the cation has more than one oxidation state

Some binary Ionic Compounds

Cation Anion(ide) Cation AnionIonic

Compound

cation (x) anion(ide) C+x A-y CyAx

lead (II) flouride PbF2Pb+2 F-1

iron (III) oxide Fe2O3Fe+3 O-2

tin (II) chloride SnCl2Sn+2 Cl-1

Use Roman numerals in parentheses to indicate the charge on metals that form more than one kind of cation.

Molecules, Ions, and Chemical Bonds

Covalent Bond: A bond that results from the sharing of electrons between atoms.

Ionic Bond: A bond that results from oppositely charged ions that are electrostaticlly attracted to each other.

Definitions of Ionic and Covalent compounds

• Ionic bonds are a result of a combination of a metal (electropositive element) and a non-metal (electronegative element).

• In ionic bonds, atoms are attracted to each other by opposite charges.

• Covalent bonds are a result of the combination of two non-metals (two electronegative elements).

• In covalent bonds, atoms are attracted to each other by a shared pair of electrons.

A Comparison of Ionic and Covalent Bonds

Points to consider: Ionic verses Covalent compounds

Point 1: Ionic compounds are usually solids (when pure)

Point 2: Ionic compounds have very high boiling and

melting points

Point 3: Covalent compounds can be either solids, liquids

or gases

Point 4: Covalent compounds have relatively lower boiling

and melting points

Why does NaCl have such high boiling and melting points?

A chemical representation of a covalent compound (ethanol)

Predict whether each compound is an ionic or molecular compound.

• KI, component in table salt

• H2O2, antioxidant

• CHCl3, anesthetic

• Li2CO3, antidepressants

Ionic: 1 metal 1 nonmetal

Molecular: 2 nonmetals

Molecular: 3 nonmetals

Ionic: 1 metal 2 nonmetals

To name nonmetals, we first have to understand a concept called Electronegativity

Electronegativity: The ability of an atom in a molecule to attract the shared electrons in a covalent bond.

Naming Covalent Compounds: Must know these prefixes

Choose which compound is more electronegative, then change the suffix to -ide

- Write the name: electropositive - electronegative

- Add the suffix “ide” to the end of the electronegative atom.

- Use the prefixes to indicate the multiplicity of the both atoms.

Example: naming N2O4

N2O4

The second element (Oxygen) is more electronegative and takes the name of the element with an “ide” modification to the ending.

The first element (Nitrogen) is more electropositive and takes the name of the element.

The prefix is added to the front of each to indicate the number of each atom.

dinitrogen tetraoxide

WORKED EXAMPLE

Give systematic names for the following compounds

Solution(a) PCl3

(b) N2O3

(c) P4O7

(d) BrF3

Phosphorus trichloride

Dinitrogen trioxide

Tetraphosphorus heptoxide

Bromine trifluoride