5.1-2 Valence Electrons and Valency

5.1 Valence Electrons

• Definition: Valence electrons are the electrons in the outermost energy level of an atom.

• Example:

• Potassium (K): The outermost energy level has 1 electron.

• Oxygen (O): The outermost energy level has 6 electrons.

Electronic Configuration of Potassium and Oxygen:

• Potassium (K): 1 valence electron.

• Oxygen (O): 6 valence electrons.

• Table of Valence Electrons for Some Elements:

Element Electronic Configuration Valence Electrons

Nitrogen (N) 2, 5 5

Fluorine (F) 2, 7 7

Phosphorus (P) 2, 8, 5 5

Chlorine (Cl) 2, 8, 7 7

Calcium (Ca) 2, 8, 8, 2 2

• Explanation:

• Nitrogen has 5 valence electrons because its outermost energy level is the L orbit, which contains 5 electrons.

• The valence electrons are critical in chemical bonding as they are the electrons involved in the formation of bonds with other atoms.

Student Activity: Find out the number of valence electrons for F (Fluorine), P (Phosphorus), Cl (Chlorine), and Ca (Calcium).

5.2 Valency

• Definition: Valency is the bonding capacity of an atom, which refers to the number of bonds an atom can form with other atoms.

• Valency of Hydrogen (H): Hydrogen’s valency is usually 1. It can form one bond with another atom.

• Determination of Valency:

• The valency of an element is determined by how many atoms of hydrogen (H) or chlorine (Cl) it can bond with.

Examples:

• Hydrogen (H) bonds with chlorine (Cl) to form HCl. Therefore, the valency of hydrogen is 1 and the valency of chlorine is also 1.

• Oxygen (O) bonds with 2 hydrogen atoms to form H2O. Therefore, the valency of oxygen is 2.

• Sodium (Na) bonds with chlorine (Cl) to form NaCl. Therefore, the valency of sodium is 1.

• Calcium (Ca) bonds with oxygen (O) to form CaO. Therefore, the valency of calcium is 2 (1 * 2 = 2).

• Variable Valency: Some elements exhibit more than one possible valency. This is known as variable valency.

• Example: Iron (Fe) has a variable valency of 2 and 3.

• Latent Valency: This refers to the difference between the highest possible valency and the active valency of an element.

• Example: In FeCl2, the active valency of iron is 2 and the highest possible valency is 3, so the latent valency is (3 - 2) = 1.

Examples:

• FeCl3: Iron has an active valency of 3 here, so there is no latent valency.

• Valency of Different Elements:

Element Valency

Na (Sodium) 1

F (Fluorine) 1

K (Potassium) 1

Cl (Chlorine) 1

Fe (Iron) 2, 3

Cu (Copper) 1, 2

Zn (Zinc) 2

Mg (Magnesium) 2

Al (Aluminum) 3

• Compounds Formed by Elements with Specific Valencies:

Element Compound Element Compound

H (Hydrogen) HCl Ag (Silver) AgCl

Li (Lithium) LiCl Na (Sodium) NaCl

Na (Sodium) NaF K (Potassium) KCl

Mg (Magnesium) MgCl2 Ca (Calcium) CaCl2

Al (Aluminum) AlCl3 Fe (Iron) FeCl2, FeCl3

Cu (Copper) CuCl, CuCl2 Pb (Lead) PbCl2, PbCl4

• Additional Explanation:

• The valency determines how an atom interacts and bonds with other atoms, influencing the types of compounds formed.

• Some elements like iron and copper can have multiple valencies, which can result in different types of compounds based on the bonding.

This concludes the section on valence electrons and valency!