Grade 10 Academic Science –– Chemistry

Covalent and Ionic Bonds

Science Perspectives 10 - Section 5.6 Pages 192-195

There are two basic types of compounds. They are distinguished by the manner in which the atoms bind to one another in the compound. These two types are called

molecular compounds

and

salts

(or equivalently

ionic compounds

).

Recall, a

molecule

is the smallest particle of a pure chemical substance that still retains its chemical composition and properties.

Molecular Compound

- These compounds are made up of molecules whose atoms bind to one another through covalent bonds.

Covalent Bond

- The electrons are

shared

between atoms.

An

ion

is an atom or group of atoms that carries a positive or negative charge as a result of having lost or gained one or more electrons.

Ionic bonds

occur due to the mutual attraction between atoms with positive and negative charges.

compound in which ions are held together in a lattice structure by ionic bonds. To form an ionic compound, there needs to be at least one metal and one non-metal. The metal element is usually the positive charge and the non-metal element is a negative charge. Ions can be single atoms, as in common table salt sodium chloride, or more complex groups such as calcium carbonate

NaCl (Sodium chloride)

form the anion (negatively charged ion) Cl − . The salts of hydrochloric acid contain chloride ions and are also called

chlorides

. An example is table salt, which is sodium chloride with the chemical formula NaCl. In water, it dissolves into Na + and Cl − ions.

Molecular Formula for Molecular Compounds

As we know, molecules consist of two or more atoms bonded to one another through covalent bonds.

The identification of these molecules is through their molecular formulas.

most simple ratio

of atoms in the molecule. For example, benzene has six carbon and six hydrogen atoms. Therefore, the ratio of carbon to hydrogen atoms is 6: 6 or simplified to 1:1. The empirical formula for benzene is CH.

Molecular Formula for Ionic Compounds

Positively charged atoms or molecules are called

cations

and negatively charged atoms or molecules are called

anions

.

As suggested, cations and anions attract one another. Conversely, cations repel other cations, as do anions and anions.

one anion and visa versa. The result is that cation-anion attractions form a large array called an ionic compound or salt. The bonds holding these ions together are called ionic bonds. However, this array has a very specific composition completely dictated by the charges on the cations and anions.

The composition of ionic compounds is determined by the requirement that the compounds must be

electrically neutral

. That is, the overall charges of the cations and anions must be zero.

Na and Cl Na is +1 charge and Cl is -1 charge. Thus, one Na cation cancels one Cl anion resulting in the formula NaCl. This formula is called the

formula unit

since it represents only one unit of the vast NaCl array or lattice.

An ionic compounds made up of single atom is a

monatomic ion

Cation Anion Compound

CaCl Br 2 Ba Cr 2+ 3+ O O 2 2 K + Ca 2+ S 2 Cl Fe 3+

ions. Most polyatomic ions are anions with one notable exception - the ammoniun cation (NH4+). The composition of salts with polyatomic ions is determined by the same rule as with monatomic ions.

SO 3 2 NH 4 + NH Li + 4 + CaSO S CO 2 2 SO 4 2 2 3 Ba Fe 2+ 3+ PO 4 2 SO 3 2 H 3 O + NH 4 + PO 4 3 HPO 4 2 CrO 4 2 Be 2+ NO 3 -

Teacher Copy – Answer Sheet

K +

Na and Cl Na is +1 charge and Cl is -1 charge. Thus, one Na cation cancels one Cl anion resulting in the formula NaCl. This formula is called the

formula unit

since it represents only one unit of the vast NaCl array or lattice.

An ionic compounds made up of single atom is a

monatomic ion

Cation Anion Compound

CaCl Fe 3+ 2 Ba 2+ Br O FeBr 3 2 BaO Cr 3+ Ca 2+ K O + 2 Cl S 2 K 2 S Cr 2 O 3

ions

. Most polyatomic ions are anions with one notable exception - the ammoniun cation (NH4+). The composition of salts with polyatomic ions is determined by the same rule as with monatomic ions.

SO 3 2 Ba SO 3 3 (PO 2 (NH 4 ) 2 CO 2 SO 4 2 CrO 4 2 CaSO 3 4 ) 2 Ba NH 4 + Fe 2 (SO 3 ) 3 H 3 O + NH 4 + Be 2+ 2+ S 2 PO 4 2 (NH 4 ) 2 S NH 4 + PO 4 3 HPO 4 2 NO 3 CO 2 2 Li + K + Fe 3+

HOMEWORK

Page 195, Questions 1-8, 12, 13