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Background theory
Published in Michael de Podesta, Understanding the Properties of Matter, 2020
At separations greater than a few atomic diameters, atoms barely interact with one another. The interactions between atoms occur when they are brought close together and are caused only by the electrical interactions between the atoms. This single fact is worth repeating: the interactions between atoms are caused only by electrical interactions. The magnitude of the interaction is dominated by the outer part of the electronic structure around the atom. The electrons in the outer part of the structure are called valence electrons. The number and distribution of the valence electrons strongly affects the physical and chemical properties of atoms, and of the substances of which the atoms are a part.
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?
Particulates and Gases
Published in W. David Yates, Safety Professional’s Reference and Study Guide, 2020
For example, sodium (Na) has an atomic number of 11, as identified on the periodic table. It is a neutrally charged atom and therefore will also have 11 electrons. There will be two electrons in the first shell, eight electrons in the second shell, and one electron in the third (or outer) shell. The electrons in the outermost shell are referred to as valence electrons. Shells with a complete number of valence electrons are considered to be inert. Shells without a complete number or one or two valence electrons tend to be more reactive. Figure 4.2 shows the various shells and their respective numbers.
Characterization of the chemical shift and asymmetry indices of praseodium, neodymium, samarium, gadolinium, and terbium compounds by wavelength dispersive X-ray fluorescence (WDXRF)
Published in Instrumentation Science & Technology, 2023
Sevil (Porikli) Durdağı, Fatma Güzel
The chemical effect is related to the number of partially filled valence electrons and unpaired electrons. This parameter is particularly sensitive to the symmetrical structures of transition metals. At the same time, the electronegativity of the atom, the structure of ligands, and the distribution of ligands around the central emitting atoms affect the symmetry state of the atom, changing the emission probabilities of characteristic X-rays. By using high-resolution counters, the characteristic X-ray intensity ratios and chemical shifts of the compounds were determined and hence the coordination numbers and their structures were estimated. More pronounced chemical effects were observed in the Ll emission lines compared to the Lƞ emission lines in this study because the former directly involves the outermost valence electrons and is strongly influenced by the chemical environment of the atom. Also, according to crystal field theory, the energy levels of the L to M shell are close together, so the outer shell energy levels and their transition probabilities are strongly influenced by the number of ligands bound by the metal atom.
Evolution in the surface modification of textiles: a review
Published in Textile Progress, 2018
Ayoub Nadi, Aicha Boukhriss, Aziz Bentis, Ezzoubeir Jabrane, Said Gmouh
Covalent chemical bonds involve the sharing of a pair of valence electrons by two atoms. The idea of immobilizing a dye molecule by covalent bond formation with reactive groups in a fibre originated in the early 1900s, but it was not until 1955 that Rattee and Stephen, working for ICI in England, developed a procedure for dyeing cotton with fibre-reactive dyes containing dichlorotriazine groups [10, 11]. Reactive dyes for cotton are the only textile colourants designed to form a covalent bond with the substrate during the application process. Reactive dyes are the most permanent of all dye types. These dyes react with cellulose either by the addition or substitution mechanism. For example, vinyl sulfonic derivatives dyes react with cellulose by the nucleophilic addition to a carbon carbon double bond as illustrated by reaction (1) [9, 10] where Cell–OH is the cellulose with a reactive hydroxyl group, Dye–SO2–CH = CH2 is the dye with its reactive vinyl sulfonic atom, and dye –SO2–CH = CH–O–Cell the dye linked to the cellulose by a covalent bond.