Transition elements are the elements that have a partially filled d orbital. These elements are also referred to as transition metals. The IUPAC definition of these elements states that any element having a d subshell that is partially filled with electrons, or any element that has the ability to form stable cations with an incompletely filled d orbital can be considered a transition element.
What are Transition Elements?
In general, any element which corresponds to the d-block of the modern periodic table, which is made up by the groups 3 to 12, is considered to be a transition element. Even the f-block elements comprising of the lanthanides and the actinides can be considered as transition metals.
However, since the f-block elements have incompletely filled f-orbitals, they are often referred to as inner transition elements or inner transition metals. An illustration detailing the position of transition metals on the periodic table along with their general electronic configurations is provided below.
It is important to note that the elements mercury, cadmium, and zinc are not considered transition elements because of their electronic configurations, which corresponds to (n-1)d10 ns2.
These elements have completely filled d orbitals in their ground states and even in some of their oxidation states. One such example is the +2 oxidation state of mercury, which corresponds to an electronic configuration of (n-1)d10.
Electronic Configuration of Transition Elements
The list of the first two rows of transition elements with their corresponding electronic configurations is tabulated below. It can be noted that in some of these elements, the configuration of electrons corresponds to (n-1)d5 ns1 or (n-1)d10 ns1. This is because of the stability provided by the half-filled or completely filled electron orbitals.
|Transition Elements||Atomic Number||Electronic Configuration|
|Sc||21||[Ar] 3d1 4s2|
|Ti||22||[Ar] 3d2 4s2|
|V||23||[Ar] 3d3 4s2|
|Cr||24||[Ar] 3d5 4s1|
|Mn||25||[Ar] 3d5 4s2|
|Fe||26||[Ar] 3d6 4s2|
|Co||27||[Ar] 3d7 4s2|
|Ni||28||[Ar] 3d8 4s2|
|Cu||29||[Ar] 3d10 4s1|
|Zn||30||[Ar] 3d10 4s2|
|Y||39||[Kr] 4d1 5s2|
|Zr||40||[Kr] 4d2 5s2|
|Nb||41||[Kr] 4d4 5s1|
|Mo||42||[Kr] 4d5 5s1|
|Tc||43||[Kr] 4d5 5s2|
|Ru||44||[Kr] 4d7 5s1|
|Rh||45||[Kr] 4d8 5s1|
|Ag||47||[Kr] 4d10 5s1|
|Cd||48||[Kr] 4d10 5s2|
It can be observed that the Aufbau principle is not followed by many transition elements like chromium. The reason for this is believed to be the relatively low energy gap between the 3d and 4s orbitals, and the 4d and 5s orbitals.
General Properties of Transition Elements
As discussed earlier, the elements zinc, cadmium, and mercury are not considered as transition elements since their electronic configurations are different from other transition metals. However, the rest of the d-block elements are somewhat similar in properties and this similarity can be observed along each specific row of the periodic table. These properties of the transition elements are listed below.
- These elements form colored compounds and ions. This color is explained by the d-d transition of electrons.
- There is a relatively low gap in energy between the possible oxidation states of these elements. The transition elements, therefore, exhibit many oxidation states.
- Many paramagnetic compounds are formed by these elements, because of the unpaired electrons in the d orbital.
- A large variety of ligands can bind themselves to these elements. Due to this, a wide variety of stable complexes are formed by transition elements.
- These elements have a large ratio of charge to the radius.
- Transition metals tend to be hard and they have relatively high densities when compared to other elements.
- The boiling points and the melting points of these elements are high, due to the participation of the delocalized d electrons in metallic bonding.
- This metallic bonding of the delocalized d electrons also causes the transition elements to be good conductors of electricity.
Thus, the electronic configurations and the properties of the transition metals are briefly discussed in this article. To learn more about the transition elements and other groups of elements in the periodic table, register with BYJU’S and download the mobile application on your smartphone.