Main Group Elements

Valence and Core Electrons

Main group elements are those found in groups 1, 2, and 13-18 of the periodic table. Understanding their electron arrangement is essential for predicting chemical behavior.

• Valence Electrons: The electrons in the outermost shell of an atom. These electrons are involved in forming chemical bonds.

• Inner Core Electrons: Electrons that are not in the outermost shell. They do not participate directly in chemical bonding.

• Total Electrons: The sum of valence and inner core electrons, equal to the atomic number (Z).

Formula:

• Number of valence electrons for main group elements = Group number

• Number of inner core electrons = Total electrons Valence electrons

Example:

How many inner core electrons would a silicon atom possess?

• Silicon atomic number (Z) = 14

• Group number = 4 (so, 4 valence electrons)

• Inner core electrons =

Electron Arrangement Example:

Chlorine (Cl), Group 7A, Z = 17

• Valence electrons = 7

• Inner core electrons =

Practice Questions

• How many valence electrons does the carbon atom possess? Answer: 4 (Group 4A)

• How many inner core and valence electrons does the nitrogen atom possess? Atomic number (Z) = 7 Group number = 5 (so, 5 valence electrons) Inner core electrons =

Summary Table: Electron Arrangement in Main Group Elements

Additional info: The concept of valence and core electrons is fundamental for understanding chemical reactivity and periodic trends in GOB Chemistry.