Using electronic configuration as the criterion, we ordinarily recognize four general type of elements: the inert gas elements, the representative elements, the transition elements, and the inner transition elements. The classification of the elements into these groups is
dependent on the extent to which the `s`, `p`, `d` and `f` orbitals are filled.
`text(Inert gases)`
a) In the atoms of these elements, the `s` and `p` subshells of the outer most shell are completely filled. The outermost electronic configuration is `ns^2 np^6`.
b) Helium is also inert gas but its electronic configuration is `1s^2`.
c) Because of stable configuration, these elements do not show chemical activity under normal conditions.
d) These are all gases under normal conditions and thus, termed as inert gases.
`text(Representative or Normal Elements)`
a) Outermost shell of these elements is incomplete. The number of electrons in the outermost shell is less than eight. The configuration of the outermost shell varies from `ns^1` to `ns^2 np^5`.
b) Inner shells are complete.
c) `s` and `p`-block elements except inert gases are called normal or representative elements. These consist of some metals, all non-metals and metalloids.
`text(Transition Elements)`
a) Last two shells of these elements namely outermost and penultimate shells are incomplete.
b) The last shell contains one or two electrons and the penultimate shell may contain more than eight up to eighteen electrons.
c) Their outermost electronic configuration is similar to `d`-block elements i.e. `(n-1)d^(1-9) ns^(0 or 1 or 2)`.
d) According to latest definition of transition elements those elements, which have partly filled `d`-orbitals in neutral state or in any stable oxidation state, are called transition elements. According to this definition `Zn`, `Cd` and `Hg` (`IIB` group) are `d`-block elements but not transition elements because these elements have `d^10` configuration in neutral as well as in stable `+2` oxidation state.
e) Because of the extra stability, which is associated with empty, half-filled, and filled subshells, there are some apparent anomalies in electronic arrangements in the transition series. This empirical rule is illustrated by the chromium and copper configuration in the first `d`-series of elements :
`quad quad` `Sc quad Ti quad V quad Cr quad Mn quad Fe quad Co quad Ni quad Cu quad Zn`
`3d` `1 quad quad 2 quad quad 3 quad quad 5 quad quad 5 quad quad quad 6 quad quad quad 7 quad quad quad 8 quad quad quad 10 quad quad 10`
`4s` `2 quad quad 2 quad quad 2 quad quad 1 quad quad 2 quad quad quad 2 quad quad quad 2 quad quad quad 2 quad quad quad 1 quad quad quad 2`
`text(Inner Transition Elements)`
a) In these elements last three shells i.e. last penultimate and pre-penultimate shells are incomplete.
b) There are two series of elements, (i) Lanthanides or rare earths from `Ce(58)` to `Lu (71)` (ii) Actinides from `Th(90)` to `Lr(103)`.
c) The last shell contains two electrons. Penultimate shell may contain eight or nine electrons and pre-penultimate shell contains more than `18` upto `32` electrons.
d) Their outermost electronic configuration is similar to `f`-block element i.e. `(n-2)f^(1-14) (n-1)s^2 (n-1)p^6 (n-1)d^(0-1) ns^2`.
e) Elements of the seventh period after atomic number `93` (i.e. actinides) are synthetic elements and are called transuranium elements.
Using electronic configuration as the criterion, we ordinarily recognize four general type of elements: the inert gas elements, the representative elements, the transition elements, and the inner transition elements. The classification of the elements into these groups is
dependent on the extent to which the `s`, `p`, `d` and `f` orbitals are filled.
`text(Inert gases)`
a) In the atoms of these elements, the `s` and `p` subshells of the outer most shell are completely filled. The outermost electronic configuration is `ns^2 np^6`.
b) Helium is also inert gas but its electronic configuration is `1s^2`.
c) Because of stable configuration, these elements do not show chemical activity under normal conditions.
d) These are all gases under normal conditions and thus, termed as inert gases.
`text(Representative or Normal Elements)`
a) Outermost shell of these elements is incomplete. The number of electrons in the outermost shell is less than eight. The configuration of the outermost shell varies from `ns^1` to `ns^2 np^5`.
b) Inner shells are complete.
c) `s` and `p`-block elements except inert gases are called normal or representative elements. These consist of some metals, all non-metals and metalloids.
`text(Transition Elements)`
a) Last two shells of these elements namely outermost and penultimate shells are incomplete.
b) The last shell contains one or two electrons and the penultimate shell may contain more than eight up to eighteen electrons.
c) Their outermost electronic configuration is similar to `d`-block elements i.e. `(n-1)d^(1-9) ns^(0 or 1 or 2)`.
d) According to latest definition of transition elements those elements, which have partly filled `d`-orbitals in neutral state or in any stable oxidation state, are called transition elements. According to this definition `Zn`, `Cd` and `Hg` (`IIB` group) are `d`-block elements but not transition elements because these elements have `d^10` configuration in neutral as well as in stable `+2` oxidation state.
e) Because of the extra stability, which is associated with empty, half-filled, and filled subshells, there are some apparent anomalies in electronic arrangements in the transition series. This empirical rule is illustrated by the chromium and copper configuration in the first `d`-series of elements :
`quad quad` `Sc quad Ti quad V quad Cr quad Mn quad Fe quad Co quad Ni quad Cu quad Zn`
`3d` `1 quad quad 2 quad quad 3 quad quad 5 quad quad 5 quad quad quad 6 quad quad quad 7 quad quad quad 8 quad quad quad 10 quad quad 10`
`4s` `2 quad quad 2 quad quad 2 quad quad 1 quad quad 2 quad quad quad 2 quad quad quad 2 quad quad quad 2 quad quad quad 1 quad quad quad 2`
`text(Inner Transition Elements)`
a) In these elements last three shells i.e. last penultimate and pre-penultimate shells are incomplete.
b) There are two series of elements, (i) Lanthanides or rare earths from `Ce(58)` to `Lu (71)` (ii) Actinides from `Th(90)` to `Lr(103)`.
c) The last shell contains two electrons. Penultimate shell may contain eight or nine electrons and pre-penultimate shell contains more than `18` upto `32` electrons.
d) Their outermost electronic configuration is similar to `f`-block element i.e. `(n-2)f^(1-14) (n-1)s^2 (n-1)p^6 (n-1)d^(0-1) ns^2`.
e) Elements of the seventh period after atomic number `93` (i.e. actinides) are synthetic elements and are called transuranium elements.