Valence Electron Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Valence Electron.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

An electron residing in the outermost (highest-energy) occupied shell of an atom, available for participation in chemical bonding through sharing, gaining, or losing. The number of valence electrons determines an element's bonding behavior and chemical reactivity.

The electrons that 'reach out' to other atoms. These do the bonding.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Valence electrons determine chemical reactivity and bonding capacity.

Common stuck point: Only outer shell electrons are valence electrons—inner ones are 'core' electrons.

Sense of Study hint: When finding valence electrons for a main-group element, use the periodic table. First locate the element's group number. Then for groups 1-2, the group number equals valence electrons. For groups 13-18, subtract 10 from the group number. Finally, remember that transition metals have more complex valence electron counts.

Worked Examples

Example 1

easy
How many valence electrons does nitrogen (Z = 7) have?

Solution

  1. 1
    Nitrogen has atomic number 7, so it has 7 electrons. Write the electron configuration by filling subshells in order of energy.
  2. 2
    Electron configuration: 1s^2\,2s^2\,2p^3. Verify: 2 + 2 + 3 = 7 electrons total.
  3. 3
    Identify valence electrons as those in the outermost shell (n = 2): 2s^2 and 2p^3 contribute 2 + 3 = 5 valence electrons.

Answer

5\text{ valence electrons}
Valence electrons occupy the highest principal energy level. For main-group elements, the group number in the periodic table indicates the number of valence electrons.

Example 2

medium
Explain why elements in Group 17 (halogens) are highly reactive, using the concept of valence electrons.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy
Determine the number of valence electrons for: (a) carbon, (b) sulfur, (c) argon.

Example 2

medium
Sodium has electron arrangement 2,8,1. How many valence electrons does it have, and is it more likely to lose one electron or gain seven?
← Back to Valence Electron Practice Mode

Background Knowledge

These ideas may be useful before you work through the harder examples.

electronelectron shell