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 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 Electron starts by naming the element, charge, and relevant protons, neutrons, or electrons.

Common stuck point: Students often know a formula related to valence electron but skip the recognition step: Am I using particle counts, nuclear charge, mass number, electron arrangement, or isotope notation to describe an atom or ion? That leads to a correct-looking substitution attached to the wrong chemical model.

Sense of Study hint: Ask: Am I using particle counts, nuclear charge, mass number, electron arrangement, or isotope notation to describe an atom or ion?

Worked Examples

Example 1

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

Answer

5 valence electrons5\text{ valence electrons}

First step

1
Nitrogen has atomic number 7, so it has 7 electrons. Write the electron configuration by filling subshells in order of energy.

Full solution

  1. 2
    Electron configuration: 1s2 2s2 2p31s^2\,2s^2\,2p^3. Verify: 2+2+3=72 + 2 + 3 = 7 electrons total.
  2. 3
    Identify valence electrons as those in the outermost shell (n=2n = 2): 2s22s^2 and 2p32p^3 contribute 2+3=52 + 3 = 5 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.

Example 3

medium
Why does Ca2+\text{Ca}^{2+} have the same electron arrangement as argon?

Example 4

hard
Predict the formula of the compound formed between magnesium and nitrogen using 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?

Example 3

easy
How many valence electrons does oxygen (group 16) have?

Example 4

easy
How many valence electrons does sodium (group 1) have?

Example 5

easy
How many valence electrons does neon (group 18) have?

Example 6

easy
How many valence electrons does carbon (group 14) have?

Example 7

easy
Which group contains elements with 7 valence electrons?

Example 8

easy
How many valence electrons does magnesium (group 2) have?

Example 9

easy
Does helium have 8 valence electrons like other noble gases?

Example 10

easy
How many valence electrons does aluminum (group 13) have?

Example 11

medium
Nitrogen is in group 15. State its valence electrons and predict the ion charge it forms.

Example 12

medium
An atom has 2 electrons in shell 1, 8 in shell 2, and 7 in shell 3. How many valence electrons does it have, and what element is it?

Example 13

medium
Why do potassium (group 1) and sodium (group 1) have similar chemical behavior?

Example 14

medium
Phosphorus (group 15) forms covalent bonds. How many bonds does it typically form, based on valence electrons?

Example 15

medium
Calcium loses electrons to bond. Using its group (2), how many electrons does it lose and what is its ion?

Example 16

medium
Sulfur (group 16) and oxygen (group 16) behave similarly. How many valence electrons drive this, and what anion charge results?

Example 17

medium
An element forms a 1+ ion by losing one electron. Which group is it in and how many valence electrons did it start with?

Example 18

medium
Why do transition metals like iron not always follow the simple group-number valence rule?

Example 19

medium
Bromine is in group 17. How many valence electrons does it have, and how many bonds or what ion charge does it adopt?

Example 20

challenge
Atom X forms an ion with charge -2 and is in period 3. Identify X, give its valence electrons, and its electron configuration as an ion.

Example 21

challenge
Element Q in period 2 forms 4 covalent bonds and has no lone pairs in QH4QH_4. How many valence electrons does Q have, and what is Q?

Example 22

challenge
Compare the energy needed to form an octet for sodium (group 1) versus chlorine (group 17). Which path (lose vs gain) does each take and why?

Example 23

easy
How many valence electrons does fluorine (group 17) have?

Example 24

easy
How many valence electrons does silicon (group 14) have?

Example 25

easy
How many valence electrons does potassium (group 1) have?

Example 26

easy
Which group has elements with 2 valence electrons?

Example 27

easy
Hydrogen has how many valence electrons?

Example 28

easy
How many valence electrons does phosphorus (group 15) have?

Example 29

medium
Write the electron configuration of sulfur and state its valence electron count.

Example 30

medium
Which element has 5 valence electrons in period 3?

Example 31

medium
Predict the charge of the most stable ion formed by aluminum.

Example 32

medium
Why are oxygen and sulfur similar in chemical behavior?

Example 33

medium
An atom has electron arrangement 2, 8, 4. How many valence electrons does it have, and what element is it?

Example 34

medium
Bromine forms Br−Br^-. Why is this charge favored?

Example 35

medium
How many bonds does carbon usually form, and why?

Example 36

medium
Sodium and magnesium are both metals in period 3. Compare their valence electron counts and likely ion charges.

Example 37

medium
Which has more valence electrons: N3−\text{N}^{3-} or N?

Example 38

hard
An ion X2−\text{X}^{2-} has electron configuration [Ne]3s23p6[Ne]3s^2 3p^6. Identify X and its valence electrons in neutral form.

Example 39

hard
Why is the second ionization energy of sodium so much higher than the first?

Example 40

hard
Element Y is in period 3 and has 3 valence electrons. Identify Y and predict its most stable cation.

Example 41

hard
How many valence electrons does the NH4+\text{NH}_4^+ ion have in total?

Example 42

hard
Determine the total valence electrons in the CO32−\text{CO}_3^{2-} ion.

Example 43

challenge
Explain why noble gases like Ne are chemically inert in terms of valence electrons.

Example 44

challenge
An element forms an oxide X2O\text{X}_2\text{O} and a chloride XCl. How many valence electrons does X have?
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Background Knowledge

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

electronelectron shell