The d-block is in the middle of the periodic table and encompasses elements from groups 3 to 12 and it also starts in the 4th period. Most of these elements are also known as transition metals because they occupy a transitional zone in properties lying between the strongly electro-positive metals of groups 1 & 2 and the weakly electro-positive metals of groups 13 to 16. Group 3 or group 12, while still counted as d-block metals, are sometimes not counted as transition metals because they do not show the chemical properties characteristic of transition metals, for example, multiple oxidation states and colored compounds. The Group 12 elements are normally called post-transition metals because they are different from the transition metals but they are still in the d-block though.
The general electronic configuration of the d-block elements is [Inert gas] (n − 1)d¹⁻¹⁰ ns⁰⁻². The period 6 and 7 transition metals also add (n − 2)f⁰⁻¹⁴ electrons.The d-block elements are all metals and most have one or more chemically active d-orbital electrons. Because there is a relatively small difference in the energy of the different d-orbital electrons, the number of electrons participating in chemical bonding can vary. The d-block elements have a tendency to exhibit two or more oxidation states, differing by multiples of one. The most common oxidation states are +2 and +3. Chromium, iron, molybdenum, ruthenium, tungsten, and osmium can have oxidation numbers as low as −4 and iridium holds the singular distinction of being capable of achieving an oxidation state of +9. The d-orbitals (four shaped as four-leaf clovers, and the tenth as a dumbbell with a ring around it) can contain up to five pairs of electrons. The d-block can hold up to ten electrons at most.
- Transition Metals
The transition metals are the elements present in the d-block of the periodic table whose atom has a partially filled d sub-shell, or which can give rise to cations with an incomplete d sub-shell. Atomic number of these metals are from 21 to 30, from 39 to 48, then 57, from 72 to 80, then 89 and from 104 to 112. Many elements like Zn, Cd, Hg, La and Ac have a highly debatable position in the transition series of elements, even though, La and Ac are also classed in the lanthanide series and actinide series respectively.
Transition metals have several general properties. They are harder and less reactive than the alkaline earth metals. They are also harder than the post transition metals. They make colorful chemical compounds with other elements. Most of them have more than one oxidation state. Like other metals, they are electrical conductors. Some of the transition metals are necessary to keep humans healthy, such as iron, zinc, and chromium. Other elements like gold or silver are non-reactive metals and do not undergo any reaction with other elements, hence called as noble metals or inert metals and do not harm or help us. There are more transition metals than any other groups in the periodic table.
- Post-Transition Metals Within d-block
Although the group 3−12 elements are commonly referred to as the transition elements, the group 12 elements are not always included. The group 12 elements are Zinc, cadmium, and mercury which are generally excluded from the transition metals as they have the electronic configuration [ ]d10s2, with no incomplete d shell. In the oxidation state +2, the ions have the electronic configuration [ ]…d10, that means they still have a complete d shell in these oxidation states. The group 12 elements Zn, Cd and Hg may therefore, under certain criteria, be classed as post-transition metals in this case. The metals such as cadmium and mercury can be harmful to our body. Mercury is the only metal present in its liquid state at room temperature and pressure.
Comments
Post a Comment