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The d-block, with the d standing for "diffuse" and azimuthal quantum number 2, is in the middle of the periodic table and encompasses elements from groups 3 to 12; it starts in the 4th period. Periods from the fourth onwards have a space for ten d-block elements.
A recognisably modern form of the table was reached in 1945 with Glenn T. Seaborg's discovery that the actinides were in fact f-block rather than d-block elements. The periodic table and law are now a central and indispensable part of modern chemistry.
Predicted values are used beyond rutherfordium (element 104). Lawrencium (element 103) has a very low first ionization energy, fitting the start of the d-block trend better than the end of the f-block trend before it. [79] In 2015, the first ionization energy of lawrencium was measured, using the isotope 256 Lr. [6] The measured value, 4.96 +0.08
A heavy, silvery d-block element, mercury is the only metallic element that is known to be liquid at standard temperature and pressure; [a] the only other element that is liquid under these conditions is the halogen bromine, though metals such as caesium, gallium, and rubidium melt just above room temperature. [b]
Since the electrons added fill the (n − 1)d orbitals, the properties of the d-block elements are quite different from those of s and p block elements in which the filling occurs either in s or in p orbitals of the valence shell. The electronic configuration of the individual elements present in all the d-block series are given below: [31]
[11] [12] [13] Yttrium is the first d-block element in the fifth period. The pure element is relatively stable in air in bulk form, due to passivation of a protective oxide (Y 2 O 3) film that forms on the surface. This film can reach a thickness of 10 μm when yttrium is heated to 750 °C in water vapor. [14]
Scandium is a chemical element with the symbol Sc and atomic number 21. It is a silvery-white metallic d-block element. Historically, it has been classified as a rare-earth element, [9] together with yttrium and the lanthanides. It was discovered in 1879 by spectral analysis of the minerals euxenite and gadolinite from Scandinavia. [10]
As a synthetic element, it is not found in nature and can only be made in a particle accelerator. It is radioactive; the most stable known isotope, 267 Rf, has a half-life of about 48 minutes. In the periodic table, it is a d-block element and the second of the fourth-row transition elements. It is in period 7 and is a group 4 element.