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Petroleum Geochemical Survey
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
Isomorphism (same form) is the similarity in crystalline structure between two or more minerals of different chemical composition. Minerals showing isomorphism contain different elements, but their structural formulae are similar. For example, the crystal structures of sodium nitrate and calcium sulfate as well as potassium hydrogen phosphate (KH2PO4) and ammonium hydrogen phosphate (NH4H2PO4) are similar and are said to be isomorphous. Crystals of these substances are almost identical. Isomorphism is exhibited by those minerals whose anions and cations have the same size or nearly the same size and same number. Chemical nature is not important for isomorphism. The size of atoms or ions and the number of the ions are important. The size of an element (cation or anion) is expressed as the atomic radius. The atomic radius is the distance from the center of the nucleus to the boundary of the surrounding electrons.
Periodic Property
Published in Mihai V. Putz, New Frontiers in Nanochemistry, 2020
Francisco Torrens, Gloria Castellano
The density of a substance depends on the mass of the atoms that compose it and the space that they occupy. The atomic radius is the average distance between the nucleus and the most peripheral electrons in the atom, expressed in picometres (pm) or angstroms (1Å = 102 pm = 10−10 m).
General Chemistry
Published in Steven L. Hoenig, Basic Chemical Concepts and Tables, 2019
Note that going across the periodic table, the atomic radius decreases. This is due to the fact that the principal energy level (principal quantum number) remains the same, but the number of electrons increase. The increase in the number of electrons causes an increase in the electrostatic attraction which causes the radius to decrease. However, going down the periodic table the principal energy level increases and hence the atomic radius increases.
A scale of absolute radii derived from electrophilicity index
Published in Molecular Physics, 2021
Hiteshi Tandon, Tanmoy Chakraborty, Vandana Suhag
Due to the screening and relativistic effects d-block elements experience contraction in their atomic size [51–53]. This well-known fact is nicely demonstrated by Figure 1. It is apparent from the figure that a constant decline in the atomic radius occurs while moving across a period. A typical contraction in size is presented by Rh (2.280 au) resulting in its lowest value in comparison to its horizontal, viz. Ru (3.039 au) and Pd (2.754 au), and vertical neighbours, viz. Co (2.585 au) and Ir (2.357 au). This inconsistency may result from unusual electronic arrangement of Rh ([Kr]4d85s1). Among the d-block, Hg (1.855 au) is noted to be the smallest of all. The reason behind this may be accounted by the relativistic contraction of its filled 6s2 shell which also supports its inert behaviour and occurrence in liquid state [22,24,36,53]. Similarly, the yellow colour of Au (2.240 au) is also a result of relativity; else it would have appeared silver as Ag [53].
Transition metals doped fullerenes: structures – NLO property relationships
Published in Molecular Physics, 2019
Shuo Liu, Feng-Wei Gao, Hong-Liang Xu, Zhong-Min Su
The optimised structures with all real frequencies of C59Co, C59Rh and C59Ir are obtained with the B3LYP method as shown in Figure 1. The main geometrical parameters of the three molecules are shown in Figure 2 and Table 1. Here to discuss the three heterofullerenes in detail, the bonds angle of heteroatoms and carbon atoms are listed. The order of angle is C–Co–C (95.55°–85.99°) > C–Ir–C (92.18°–81.57°) > C-Rh-C (90.64°–81.39°). The bonds length of C-Co are in the range of 1.814–1.847 Å; while the bonds length of C–Rh and C–Ir are little longer than C–Co, they are in the range of 1.931–1.965 Å and 1.918–1.964 Å, respectively. Data above signifies that the Rh-C bonds length are longer than Co-C bonds and Ir-C bonds, the bond angle also confirmed it. Our group has investigated C59N and C59B cage radicals [60], according to the study, it is not hard to discover that the heterofullerenes’s (C59Co, C59Rh and C59Ir) bonds are much longer than corresponding bonds of C59N and C59B, where bonds length of C–N are in range of 1.408–1.424 Å and bonds length of C-B are in range of 1.525–1.549 Å. This shows that atomic radius has an important influence on bond length.