Answer:
Explanation:
In chemistry and physics, a valence electron is an outer shell electron that is associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed; in a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair.
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. In this way, a given element's reactivity is highly dependent upon its electronic configuration. 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.
An atom with a closed shell of valence electrons (corresponding to an electron configuration s2p6 for main group elements or d10s2p6 for transition metals) 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 less 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.
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 (jump) to an outer shell; this is known as atomic excitation. Or the electron can even break free from its associated atom's shell; this is ionization to form a positive ion. When an electron loses energy (thereby causing a photon to be emitted), then it can move to an inner shell which is not fully occupied.
ContentsOverview
Electron configuration
The electrons that determine valence – how an atom reacts chemically – are those with the highest energy.
For a main group element, the valence electrons are defined as those electrons residing in the electronic shell of highest principal quantum number n.[1] Thus, the number of valence electrons that it may have depends on the electron configuration in a simple way. For example, the electronic configuration of phosphorus (P) is 1s2 2s2 2p6 3s2 3p3 so that there are 5 valence electrons (3s2 3p3), corresponding to a maximum valence for P of 5 as in the molecule PF5; this configuration is normally abbreviated to [Ne] 3s2 3p3, where [Ne] signifies the core electrons whose configuration is identical to that of the noble gas neon.
However, transition elements have partially filled (n − 1)d energy levels, that are very close in energy to the ns level.[2] So as opposed to main group elements, a valence electron for a transition metal is defined as an electron that resides outside a noble-gas core.[3] Thus, generally, the d electrons in transition metals behave as valence electrons although they are not in the outermost shell. For example, manganese (Mn) has configuration 1s2 2s2 2p6 3s2 3p6 4s2 3d5; this is abbreviated to [Ar] 4s2 3d5, where [Ar] denotes a core configuration identical to that of the noble gas argon. In this atom, a 3d electron has energy similar to that of a 4s electron, and much higher than that of a 3s or 3p electron. In effect, there are possibly seven valence electrons (4s2 3d5) outside the argon-like core; this is consistent with the chemical fact that manganese can have an oxidation state as high as +7 (in the permanganate ion: MnO−
4).
The farther right in each transition metal series, the lower the energy of an electron in a d subshell and the less such an electron has valence properties. Thus, although a nickel atom has, in principle, ten valence electrons (4s2 3d8), its oxidation state never exceeds four. For zinc, the 3d subshell is complete in all known compounds, although it does contribute to the valence band in some compounds.[4]
The d electron count is an alternative tool for understanding the chemistry of a transition metal.
The number of valence electrons
The number of valence electrons of an element can be determined by the periodic table group (vertical column) in which the element is categorized. With the exception of groups 3–12 (the transition metals), the units digit of the group number identifies how many valence electrons are associated with a neutral atom of an element listed under that particular column.
Helium is an exception: despite having a 1s2 configuration with two valence electrons, and thus having some similarities with the alkaline earth metals with their ns2 valence configurations, its shell is completely full and hence it is chemically very inert and is usually placed in group 18 with the other noble gases.
id say it will be c or d but have fun
