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Chemical Bond III: Complements
Published in Franco Battaglia, Thomas F. George, Understanding Molecules, 2018
Franco Battaglia, Thomas F. George
According to an even more simplified model, valence electrons are considered to move freely within a box bounded by the metal walls. The bond keeping the crystal assembled it is referred to as metallic bond, which consists of the bond formed between the negatively charged electron “sea” (i.e., those electrons which in the isolated atom had been called valence electrons) into which a positive-ion lattice is submerged, with the electrostatic interaction acting as a “glue” for the entire system. From this point of view, the metallic bond may be thought as a special type of covalent bond, where some electrons of each atom do not have the chance of forming a bond with the nearby atoms. Alternatively, the metallic bond may be thought as a special type of ionic bond: as in sodium chloride the low ionization energy allows sodium atoms to give up an electron (readily taken by high-electron-affinity chlorine atoms) so that a bond is established between Na+ cations and Cl– anions, similarly in elementary sodium a bond is established between Na+ cations and electrons, e–, whose small mass does not allow them to stay localized around an equilibrium position around which are instead constrained the Cl– anions.
Introduction
Published in Peter E. J. Flewitt, Robert K. Wild, Physical Methods for Materials Characterisation, 2017
Peter E. J. Flewitt, Robert K. Wild
Figure 1.5 shows the five types of interatomic bond which can exist for all materials, either individually or in combinations. They are (a) ionic, (b) covalent, (c) metallic, (d) molecular and (e) hydrogen. In the case of the ionic bond, the atoms either gain or lose an electron so that their outer electron shell is complete. As a consequence, the atoms are electrically charged, either positively or negatively, and thereby attract atoms of opposite charge. For the covalent bond, pairs of atoms share outer electrons to fill the outer electron shells; this differs from the metallic bond where all atoms share the valence electrons. The molecular bond (van der Waals) arises from the displacement of charge within electrically neutral atoms or molecules producing a weak attractive force between them. The hydrogen bond is weak and mediated by the hydrogen atom. It arises because hydrogen is a small atom and the charge is easily displaced.
The Structure of Solids
Published in Joseph Datsko, Materials Selection for Design and Manufacturing, 2020
The metallic bond is a special type of covalent bond wherein the positively charged nuclei of the metal atoms are attracted by electrostatic force to the valence electrons that surround them. Unlike the common covalent bond which is directional, i.e., between a pair of atoms, the metallic bond is nondirectional and each nucleus attracts as many valence electrons as possible. This leads to a dense packing of the atoms, and thus the most common crystal structures of the metal are close-packed: face- and body-centered cubic and hexagonal close-packed.
Parameters effect on electrical conductivity of copper fabricated by rapid manufacturing
Published in Materials and Manufacturing Processes, 2020
Gurminder Singh, Sunpreet Singh, Jagtar Singh, Pulak M Pandey
The electrical conductivity in the metals generally uses the metallic bonds and the free electrons for the transportation of the electric energy. The metallic bonds are having crystalline structures and weak attraction forces from the valence electron of the metal and these valence electrons can break from the host and move freely between the potential. The metals, with valence electrons in the outer ring, are possessing weak attraction forces and, therefore, offer high electrical conductivity. For instance, gold (Ag), silver (Au), and copper (Cu) possess one valence electron and have higher electrical conductivity when compared to other metals. However, due to the high cost of Ag and Au, Cu is highly popular in different applications such as microchips, electrical switches, different types of electrodes, catalysis, heat sinks, magnetrons in microwaves, etc. Commercial technologies such as casting, machining, forging and welding, etc. are being extensively used for several years to fabricate pure-Cu products. However, such processes are unsuitable for creating complex shapes of pure-Cu and this is one of the driving forces to invent novel methods for creating optimized shape of pure-Cu.[1] Indeed, additive manufacturing (AM), specifically rapid manufacturing (RM), technique of this modern era has shown the capability to fabricate complex shapes.[2–4]
Temperature, current density and cobalt concentration effects on electrodeposited anticorrosive cobalt-tungsten alloys using factorial experiment design and ANOVA techniques
Published in Transactions of the IMF, 2019
M. B. Porto, D. G. Portela, A. F. de Almeida Neto
For coatings obtained in experiments 1 and 3, amorphous structures are formed by random atomic arrangements and without symmetry or long-range order. A class of solid materials which has an amorphous structure stands out, since they have widely varying characteristics. Components are bonded together by metallic bonds and therefore have high electrical and thermal conductivity as well as a high degree of ductility. These materials also generally exhibit certain qualities such as being easily magnetisable, having high hardness, toughness, and corrosion resistance, and having low thermal expansion. When constituted of appropriate elements, these glassy metals have high resistance to corrosion.20Figure 6 shows experiments 1 and 3.
Machine learning models for occurrence form prediction of heavy metals in tailings
Published in International Journal of Mining, Reclamation and Environment, 2023
Jiashuai Zheng, Mengting Wu, Zaher Mundher Yaseen, Chongchong Qi
More specifically, the atomic mass generally correlated positively with F1–F4 and negatively with F7. For F5 and F6, the atomic mass tended to be stable in general; only one fluctuation was recorded around a normalised atomic mass of 0.18, marked by a sudden increase followed by a decrease to the original trend. The above results suggest that an increase in atomic mass might result in greater element mobility in tailings. With increasing EC, F1–F4 first decreased and then increased. In contrast, F7 remained unchanged at normalised EC < 0.2; subsequently, F7 first increased and then decreased as the EC value increased. The reason for this observation is that F7 is a difficult fraction to extract, whereas fractions F1 to F4 are relatively easy to extract; therefore, the influence mechanisms of input variables on fractions F1–F4 were often the opposite of those for fraction F7. Similarly, in the study by Qi et al. [55], it was shown that when EC exceeded a certain limit (more than 2, which is 0.85 of the normalised data in our Figure 10), the corresponding F1 levels increased. This is because when the EC is large, fractions F1–F4 increase because metals are more likely to form ionic or covalent bonds. This is because metallic bonding occurs when metal atoms share their valence electrons to form a lattice of positive ions surrounded by a sea of delocalised electrons [52,56]. Metals with low EC values are more likely to form metallic bonds because their valence electrons are weakly attracted to the nucleus, thus allowing them to move freely throughout the metal lattice. In general, as the EC of an element increases, it tends to form more ionic or covalent bonds rather than metallic bonds [52,57]. Furthermore, we also found that with increasing total element concentration, there was relatively little change in occurrence forms, indicating that total element concentration was a relatively less important factor. These findings suggest that PDPs could be applied to assess the overall impact of input variables on HM occurrence forms.