Block (periodic table)
A block of the periodic table is a set of elements unified by the atomic orbitals their valence electrons or vacancies lie in.
[2] Each block is named after its characteristic orbital: s-block, p-block, d-block, f-block and g-block.
The block names (s, p, d, and f) are derived from the spectroscopic notation for the value of an electron's azimuthal quantum number: sharp (0), principal (1), diffuse (2), and fundamental (3).
Succeeding notations proceed in alphabetical order, as g, h, etc., though elements that would belong in such blocks have not yet been found.
The s-block and p-block together are usually considered main-group elements, the d-block corresponds to the transition metals, and the f-block corresponds to the inner transition metals and encompasses nearly all of the lanthanides (like lanthanum, praseodymium and dysprosium) and the actinides (like actinium, uranium and einsteinium).
Helium is an s-block element, with its outer (and only) electrons in the 1s atomic orbital, although its chemical properties are more similar to the p-block noble gases in group 18 due to its full shell.
Some ... other s-block elements are used in medicine (e.g. Li and Ba) and/or occur as minor but useful contaminants in Ca bio-minerals e.g. Sr…These metals display only one stable oxidation state [+1 or +2].
The s-block, with the s standing for "sharp" and azimuthal quantum number 0, is on the left side of the conventional periodic table and is composed of elements from the first two columns plus one element in the rightmost column, the nonmetals hydrogen and helium and the alkali metals (in group 1) and alkaline earth metals (group 2).
The metals of the s-block (from the second period onwards) are mostly soft and have generally low melting and boiling points.
The p-block, with the p standing for "principal" and azimuthal quantum number 1, is on the right side of the standard periodic table and encompasses elements in groups 13 to 18.
Alternatively, the p-block can be described as containing post-transition metals; metalloids; reactive nonmetals including the halogens; and noble gases (excluding helium).
The p orbital consists of six lobed shapes coming from a central point at evenly spaced angles.
The p-block elements show variable oxidation states usually differing by multiples of two.
The ... elements show a horizontal similarity in their physical and chemical properties as well as the usual vertical relationship.
Chromium, iron, molybdenum, ruthenium, tungsten, and osmium can have formal oxidation numbers as low as −4; iridium holds the singular distinction of being capable of achieving an oxidation state of +9, though only under far-from-standard conditions.
The f-orbital electrons are less active in the chemistry of the period 6 f-block elements, although they do make some contribution;[5] these are rather similar to each other.
This is a holdover from early erroneous measurements of electron configurations, in which the 4f shell was thought to complete its filling only at lutetium.
