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Structure of Molecules
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
A dipole is the separation of charges within a molecule between two covalently bonded atoms or atoms that share an ionic bond. A dipole is the unsymmetrical dispersion of electron density in a covalent bond toward a concentration of higher electron density in one atom of that bond, in a molecule that has at least one polarized covalent bond. A polarized covalent bond has a partial negative charge on one atom and a partial positive charge on the other. The term dipole can also be used in connection with an entire molecule, where the electron density is not symmetrically dispersed. What is dipole moment?
Quantum Mechanics and Its Applications
Published in Sergey Edward Lyshevski, Nano- and Micro-Electromechanical Systems, 2018
There exists the endless diversity of organic carbon-based molecules, and the versatility of carbon in molecular architectures is fascinating. Valence is the number of bonds an atom can form, and the number of bonds is equal to the number of electrons required to complete the valence (outermost) electron shell. For 6C, the electron configuration is 1s2 2s2 2p2. Atoms with incomplete valence shells interact with certain other atoms to complete valence shells by sharing electrons. A covalent bond is the sharing of a pair of valence electrons by two atoms. Hydrogen has one valence electron in the first shell, but the shell capacity is two electrons. Therefore, for example, four hydrogen atoms satisfy the valence of one carbon atom forming methane (atoms share valence electrons), and the molecular formula is
Glossary of scientific and technical terms in bioengineering and biological engineering
Published in Megh R. Goyal, Scientific and Technical Terms in Bioengineering and Biological Engineering, 2018
Covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding.
Strategies for ultrahigh outputs generation in triboelectric energy harvesting technologies: from fundamentals to devices
Published in Science and Technology of Advanced Materials, 2019
At the beginning of the research, most researchers focused on the electronegativity of polymers because it was deeply related with charge-neutrality level. Electronegativity refers to the ability of an atom to attract the electrons shared by atoms in a covalent bond. The higher the value of the electronegativity, the more strongly the atom attracts the electrons. Fluoro group (-F) has the highest tendency to attract electrons, thus, various polymers with the fluoro group such as PTFE, FEP and polyvinylidene fluoride (PVDF) were tested and quite high instantaneous outputs were reported in various-type TENGs [45,49,50]. Recently, the surface of PDMS in an arch-shaped TENG was modified via fluorocarbon (C4F8) plasma treatment (Figure 3(a,b)), the TENG output peak voltage increased sharply from 124 V to 265 V after eight-cycle plasma treatment (Figure 3(c)). The energy volume density of TENG was enhanced by approximately 278%, compared with the TENG fabricated with pristine PDMS layer. The enhancement of the outputs was attributed to the increase of the ionization energy by fluorination and the formation of PDMS micro/nano hierarchical structures by the treatment (Figure 3(d,e)).