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The lanthanide contraction is the greater-than-expected decrease in atomic radii and ionic radii of the elements in the lanthanide series, from left to right. It is caused by the poor shielding effect of nuclear charge by the 4f electrons along with the expected periodic trend of increasing electronegativity and nuclear charge on moving from left to right.
A direct consequence is that, during the formation of coordination bonds, the REE behaviour gradually changes along the series. Furthermore, the lanthanide contraction causes the ionic radius of Ho 3+ (0.901 Å) to be almost identical to that of Y 3+ (0.9 Å), justifying the inclusion of the latter among the REE.
The lanthanide contraction, i.e. the reduction in size of the Ln 3+ ion from La 3+ (103 pm) to Lu 3+ (86.1 pm), is often explained by the poor shielding of the 5s and 5p electrons by the 4f electrons. [18] Lanthanide oxides: clockwise from top center: praseodymium, cerium, lanthanum, neodymium, samarium and gadolinium.
The d-block contraction (sometimes called scandide contraction [1]) is a term used in chemistry to describe the effect of having full d orbitals on the period 4 elements. The elements in question are gallium , germanium , arsenic , selenium , bromine , and krypton [ citation needed ] .
The lanthanide contraction only partially accounts for this anomaly. [11] Because the 6s 2 orbital is contracted by relativistic effects and may therefore only weakly contribute to any chemical bonding, Hg–Hg bonding must be mostly the result of van der Waals forces. [11] [13] [14] Mercury gas is mostly monatomic, Hg(g).
The d-block contraction is less pronounced than the lanthanide contraction but arises from a similar cause. In this case, it is the poor shielding capacity of the 3d-electrons which affects the atomic radii and chemistries of the elements immediately following the first row of the transition metals, from gallium (Z = 31) to bromine (Z = 35). [19]
The wider the electron shells are in space, the weaker is the electric interaction between the electrons and the nucleus due to screening. Further, because of differences in orbital penetration, we can order the screening strength, S, that electrons in a given orbital (s, p, d, or f) provide to the rest of the electrons thusly: > > > ().
Hence this causes a cascade of electron changes, which finally results in the outermost electron shells contracting and getting closer to the nucleus. Group 4: Hafnium's near similarity in IE with zirconium. The effects of the lanthanide contraction can still be felt after the lanthanides. [26]