Valence electron
Outermost electrons that govern chemical bonding and reactivity.
Valence electrons are the electrons in the outermost shell of an atom that can participate in the formation of chemical bonds if the outermost shell is not closed. Their presence determines an element's chemical properties, including its valence and reactivity, which are highly dependent upon the element's electronic configuration. For main-group elements, valence electrons exist only in the outermost electron shell; for transition metals, they can also reside in an inner shell.
- field
- Chemistry and physics
- known_for
- Determining chemical bonding and reactivity of elements
- key_concept
- Electrons in the outermost shell that can form chemical bonds
Lore & Background
In chemistry and physics, valence electrons are defined as electrons in the outermost shell of an atom, and they can participate in the formation of a chemical bond if the outermost shell is not closed. In a single covalent bond, a shared pair forms with both atoms in the bond each contributing one valence electron. The presence of valence electrons can determine the element's chemical properties, such as its valence—whether it may bond with other elements and, if so, how readily and with how many. For a main-group element, a valence electron can exist only in the outermost electron shell; for a transition metal, a valence electron can also be in an inner shell.
Reader's Guide
The concept of valence electrons is fundamental to understanding chemical reactivity and bonding. An atom with a closed shell of valence electrons (corresponding to a noble gas configuration) tends to be chemically inert. Atoms with one or two valence electrons more than a closed shell are highly reactive due to the relatively low energy to remove the extra valence electrons to form a positive ion. An atom with one or two electrons fewer than a closed shell is reactive due to its tendency either to gain the missing valence electrons and form a negative ion, or else to share valence electrons and form a covalent bond. The number of valence electrons of an element can be determined by the periodic table group: in groups 1–12, the group number matches the number of valence electrons; in groups 13–18, the units digit of the group number matches the number of valence electrons. Helium is an exception: despite having a 1s2 configuration with two valence electrons, its shell is completely full and hence it is chemically very inert and is usually placed in group 18 with the other noble gases. The valence shell is the set of orbitals which are energetically accessible for accepting electrons to form chemical bonds. For main-group elements, the valence shell consists of the ns and np orbitals in the outermost electron shell. For transition metals the orbitals of the incomplete (n−1)d subshell are included, and for lanthanides and actinides incomplete (n−2)f and (n−1)d subshells. As a general rule, a main-group element (except hydrogen or helium) tends to react to form a s2p6 electron configuration, called the octet rule, because each bonded atom has 8 valence electrons including shared electrons. Similarly, a transition metal tends to react to form a d10s2p6 electron configuration, called the 18-electron rule.
Did You Know?
- Similar to a core electron, a valence electron has the ability to absorb or release energy in the form of a photon.
- An energy gain can trigger the electron to move to an outer shell, known as atomic excitation.
- The maximum known number of valence electrons is 16 in ytterbium and nobelium, though no oxidation state higher than +9 is known for any element.
- For a transition metal, a valence electron can also be in an inner shell, such as the (n−1)d subshell.
Frequently Asked Questions
Who is Valence electron?
Valence electron is the outermost-shell electron of an atom that remains available to participate in bond formation whenever that shell has not yet reached a closed configuration. Think of it as the atom's 'public-facing' electron, the one that actually gets to interact with neighboring atoms.
What are Valence electron's powers/role?
Its core role is to drive chemical bonding and dictate how reactive an element will be. The number and arrangement of these electrons in the outermost shell set the element's valence and largely determine its chemical personality.
Where does Valence electron live?
For main-group elements, it resides strictly in the outermost electron shell. For transition metals, however, it can also be tucked into an inner d-subshell, giving those elements a more complex bonding repertoire.
How does Valence electron's story end?
Its arc concludes when the outermost shell reaches a stable, closed configuration—typically by sharing, gaining, or losing electrons to form a chemical bond. At that point the atom's reactivity drops sharply and the electron is no longer 'available' in the same way.
Why is Valence electron important?
Without valence electrons, atoms would have no mechanism for forming bonds, and the vast landscape of molecular chemistry would simply not exist. They are the single most important factor linking an element's electronic configuration to its observable chemical behavior.
More in Chemical Bonding And Structure 1-21
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