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Introduction to Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
The chemical bond is the attractive force between the atoms in a molecule that binds together the atoms. It originates from the tendency of atoms to acquire the stable inert gas configuration. The main types of bonds are as follows: (i) ionic or electrovalent bond in which electrons are transferred from one atom to another forming positive and negative ions that stick together by electrostatic force; (ii) covalent bond in which the atoms are held together by sharing electron pairs; bonds formed by sharing one, two, or three pairs of electrons are called single, double, or triple bonds respectively; (iii) hydrogen bond, in which a hydrogen atom attached to one of the three elements, fluorine, oxygen, or nitrogen, is able to form a bridge with another one of these three elements; and (iv) metallic bond, forming in metals, which, due to their low ionization energies, lose one or more of their outer shell electrons, becoming positive ions so that the metal is pictured as a sea of free mobile electrons in which positive ions are immersed. The free electrons are said to be delocalized. Delocalization is the spreading of a molecule’s electrons over the molecule.
Background theory
Published in Michael de Podesta, Understanding the Properties of Matter, 2020
It is unusual on our planet to find matter in elemental form. Normally we encounter matter in which there are many types of atoms. The atoms are held together by electrical interactions between the outer electrons on each atom, known as chemical bonds. A set of atoms that are bonded together chemically is known as a molecule. Molecules range in size from two atoms to thousands of atoms. For example N2 , O2 are two-atom molecules composed (as the subscript indicates) of two atoms of nitrogen and oxygen respectively. Examples of three atom molecules are H2O (two atoms of hydrogen and one of oxygen) and CO2 (one atom of carbon and two of oxygen). Molecules with thousands of atoms have chemical formulae which are too complicated to list here.
Structure of Molecules
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
Valence electrons are outer shell electrons that are associated with an atom and participate in the formation of a chemical bond. Valence electrons can participate in the formation of a chemical bond if the outer shell is not full. As practical matter, valence electrons are the number of electrons in the outermost shell of an atom that are available to form a covalent bond with another atom. Boron has three valence electrons, carbon has four valence electrons, nitrogen three, oxygen two, and fluorine has one. How many valence electrons does N have? O?
Refractive Index Measurements of Solid Hydrogen Isotopologues
Published in Fusion Science and Technology, 2023
Jiaqi Zhang, Akifumi Iwamoto, Keisuke Shigemori, Masanori Hara, Kohei Yamanoi
Isotopes are atoms of an element with different masses. Isotope effects are the variations of certain chemical and physical properties of an element and its constituent molecules based on mass differences. The isotope effects of hydrogen isotopologues are the most evident because of the large disparity in the relative mass.1 Isotope effects induce isotopologue fractionation, namely, the enrichment of the heavier and lighter isotopologues in different phases during a phase transition. For example, among the techniques of cryogenic distillation for hydrogen isotopologue separation, when the hydrogen isotopologue mixture evaporates, hydrogen becomes enriched in the vapor phase while tritium tends toward the liquid phase.1 Thus, it is important to monitor the isotopologue concentration of the liquid mixture in real time.2
Synthesis and characterization of Pd supported on methane diamine (propyl silane) functionalized Fe3O4 nanoparticles as a magnetic catalyst for synthesis of α-aminonitriles and 2-methoxy-2-phenylacetonitrile derivative via Strecker-type reaction under ambient and solvent-free conditions
Published in Inorganic and Nano-Metal Chemistry, 2021
Mingzhe Sun, Wei Liu, Wei Wu, Qun Li, Di Song, Li Yan, Majid Mohammadnia
Nanoscience is the investigation of phenomenon on a nanometer scale. Atoms are a few tenths of a nanometer in diameter, and molecules are usually a few nanometers in size.[1] Nanomaterials are submicron types (mainly diameters ranging from 1 to 100 nm) made of different inorganic or organic compounds, which have many new properties compared with the bulk materials.[2] In fact, nanomaterials are of great interest in organic synthesis due to their highly small size and large surface-to-volume ratio, which lead to both chemical and physical differences in their characteristics compared to the bulk of the same chemical composition. These properties are responsible for their excellent catalytic activity.[3]
Sign use and cognition in automated scientific discovery: are computers only special kinds of signs?
Published in International Journal of General Systems, 2018
Until the mid-1930s, the picture of the building blocs from which all matter was made had been clear and simple. Atoms consisted of a nucleus and electrons orbiting around it. The nucleus, in turn, was built from protons and neutrons. But with the advent of particle accelerators producing high energies and the development of cosmic rays research, the hitherto “elementary” particles began to exhibit internal structure. When in the 1950s the number of known particles exceeded 100, physicists began to look for some ordered pattern in this perplexing plethora of “elementary” particles. By 1963, particles had been grouped into so called families according to their properties (called quantum numbers). In 1964, Gell-Mann and Ne’eman found the correct representations for all known families on purely theoretical ground. They introduced into theory entirely new particles of fractional charge, called quarks. They postulated that some particles consisted of three quarks and others of a quark anti-quark pair. Now physicists believe that there are still three more quarks so that the total number of quarks equals six.