How do you calculate valence electrons from the periodic table?

For main-group elements (groups 1–2 and 13–18), the group number tells you the number of valence electrons: group 1 has 1, group 2 has 2, group 13 has 3, up to group 18 with 8 (except helium, which has 2). For transition metals, you must look at the electron configuration and count electrons in the outermost s and d subshells that participate in bonding.

How many valence electrons does carbon have?

Carbon is in group 14 and has the electron configuration 1s2 2s2 2p2. The outer shell (n = 2) has 2 + 2 = 4 electrons, so carbon has 4 valence electrons.

Why are valence electrons important in chemistry?

Valence electrons are the electrons involved in forming chemical bonds. They determine how atoms interact, what kinds of bonds they form, the shape of molecules, and many physical and chemical properties such as reactivity, polarity, and ion formation.

Valence Electrons Calculator

Q: Are valence electrons always the same as the outer-shell electrons?

For many main-group elements, valence electrons are the same as the electrons in the outermost shell. For transition metals and inner transition metals, some electrons in an inner d or f subshell can also behave as valence electrons, so the simple outer-shell rule does not always apply.

Type an element symbol (H, C, Fe), name (oxygen), or atomic number (8) to instantly see its valence electrons, electron configuration, and Lewis dot diagram.

Interactive Valence Electrons Finder

Element (symbol, name, or atomic number)

Works for all 118 elements. For transition metals, typical valence electron counts are shown (may vary by oxidation state).

Valence definition

Use “Main-group rule” for quick chemistry class answers; “Outer-shell electrons” for a more configuration-based view.

Element summary

Element: –
Symbol: –
Atomic number (Z): –
Period: –
Group: –
Block: –

Valence electrons

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Electron configuration

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Lewis dot diagram (simplified)

Enter an element to see its Lewis dots

Quick table: valence electrons for common elements

Element	Symbol	Group	Valence electrons

What are valence electrons?

Valence electrons are the electrons in an atom that can participate in chemical bonding. For most elements you meet in general chemistry, these are the electrons in the outermost electron shell (highest principal quantum number n).

Because chemical bonds involve sharing, gaining, or losing electrons, valence electrons largely determine an element’s reactivity, the types of bonds it forms, and the structure of molecules.

How to determine valence electrons from the periodic table

For main-group elements (s- and p-block, groups 1–2 and 13–18), you can use the group number:

Group 1 (alkali metals): 1 valence electron (e.g., H, Li, Na)
Group 2 (alkaline earth metals): 2 valence electrons (e.g., Be, Mg, Ca)
Group 13: 3 valence electrons (e.g., B, Al)
Group 14: 4 valence electrons (e.g., C, Si)
Group 15: 5 valence electrons (e.g., N, P)
Group 16: 6 valence electrons (e.g., O, S)
Group 17 (halogens): 7 valence electrons (e.g., F, Cl)
Group 18 (noble gases): 8 valence electrons (except He, which has 2)

Rule of thumb (main-group elements):

\[ \text{Valence electrons} = \begin{cases} \text{Group number} & \text{for groups 1–2} \\ \text{Group number} - 10 & \text{for groups 13–18} \end{cases} \]

Example: carbon

Carbon is in group 14 and period 2. Its electron configuration is \(1s^2 2s^2 2p^2\). The outer shell is \(n = 2\), which contains \(2 + 2 = 4\) electrons, so carbon has 4 valence electrons.

Valence electrons vs. outer-shell electrons

For many main-group elements, valence electrons are simply the electrons in the outermost shell. However, for transition metals and inner transition metals, some electrons in an inner d or f subshell can also behave as valence electrons.

That’s why our calculator offers two modes:

Main-group rule: Uses group number; matches most textbook and exam conventions.
Outer-shell electrons: Counts electrons in the highest n shell from the full configuration.

Lewis dot diagrams and valence electrons

A Lewis dot diagram represents valence electrons as dots around the element symbol. For example, oxygen (6 valence electrons) is drawn with six dots arranged around “O”.

Our calculator automatically generates a simple Lewis dot pattern based on the valence electron count you choose. This is especially helpful when learning how to draw Lewis structures for molecules and ions.

Common pitfalls and special cases

Helium: Group 18 but only 2 electrons total → 2 valence electrons.
Hydrogen: Often treated as having 1 valence electron and aiming for a duet (2 electrons) rather than an octet.
Transition metals: Valence electrons can include both outer s and partially filled d subshells; the exact count depends on oxidation state and context.
Expanded octets: Elements in period 3 and beyond (e.g., P, S, Cl) can sometimes use d orbitals to form more than 8 valence electrons in bonding descriptions.