Physical Science SHS 4.1 Counting Valence Electrons

Lesson Overview

• Lesson Topic: Counting Valence Electrons

Objectives

• Determine the number of valence electrons of an atom.

Valence Electrons

• Definition: Electrons in the outermost shell of an atom.

• Role: Participate in chemical bond formation.

• Periodic Table: Provides mass number and atomic number information.

The Periodic Table of Elements

• Organized by IUPAC rules.

• Divided into sections based on electron configurations: Representative Elements, Transition Metals, Lanthanides, and Actinides.

Representative Elements

• Located in the s- and p-blocks of the periodic table.

• Valence electrons in the outermost shell with the highest principal quantum number (n).

• Examples:

  • Silicon: 1s² 2s² 2p⁶ 3s² 3p² → 4 valence electrons (n=3).

  • Beryllium: 1s² 2s² → 2 valence electrons (n=2).

Group Number Systems

• CAS and IUPAC Group Numbers with Valence Electrons:

  • 1A: 1, 2A: 2, 3A: 3, 4A: 4, 5A: 5, 6A: 6, 7A: 7, 8A: 8.

Transition Metals

• Located in the d-block; groups 3-12.

• Valence electrons vary as d subshells fill.

• Example:

  • Zinc (Group 12): 2 valence electrons.

  • Copper (Group 11): 1-2 valence electrons.

Inner Transition Metals

• Rare earth metals (Lanthanides and Actinides).

• Vary in oxidation states; all are radioactive.

Determining Valence Electrons

• For individual atoms: Refer to group number.

• For compounds: Total the valence electrons of each atom.

  • Example for Ca: Group 2A → 2 valence electrons.

  • Example for NO₂: N (5) + 2*O (6) = 17 valence electrons total.

Key Points

1. Valence electrons found in the outermost shell.

2. Periodic table categorizes elements by their electron configurations.

3. Representative elements have a clear pattern for determining valence electrons.

4. Transition and inner transition metals have varying valence electron counts based on specific characteristics.

5. The total valence electrons in a compound is the sum of the individual atoms' valence electrons.