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Introduction to Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
Elements are divided into three classes: metals, nonmetals, and metalloids. Metals form positively charged ions (cations) by the loss of electrons from their atoms; they have positive valency. Nonmetals form negatively charged ions (anions) by the gain of electrons by their atoms; they have negative valency. Metals (except mercury, Hg, which is a liquid) are solid at room temperature. In general, metals, for example, gold (Au), silver (Ag), copper (Cu), and aluminum (Al), etc., are lustrous (shiny), malleable (can be shaped by hammering), ductile (capable of being drawn into a wire, not brittle, moldable), and good conductors of heat and electricity. Examples of nonmetals are argon (Ar), bromine (Br), carbon (C), chlorine (Cl), fluorine (F), helium (He), iodine (I), krypton (Kr), neon (Ne), nitrogen (N), oxygen (O), phosphorus (P), radon (Rn), selenium (Se), sulfur (S), and xenon (Xe). Nonmetals are generally solids or gases, except for bromine, which is a liquid.
Applied Chemistry and Physics
Published in Robert A. Burke, Applied Chemistry and Physics, 2020
Nonmetal compounds are formed from nonmetal elements. For example, when the nonmetal carbon is combined with the nonmetal sulfur, the compound formed is carbon disulfide, which is a poison by absorption and is a highly flammable, dangerous fire and explosion risk; has a wide flammable range from 1%–50% and can be ignited by friction. Carbon disulfide also has a low ignition temperature and can be ignited by a steam pipe or light bulb. Nonmetal compounds can be represented in three ways: chemical name, molecular formula and structural formula. In the above example, carbon disulfide is the chemical name, the molecular formula is CS2 and its structural formula is shown in Figure 3.40.
Review of Basic Chemistry and Geology
Published in Arthur W. Hounslow, Water Quality Data, 2018
Metals lose electrons, conduct electricity and heat, and are generally ductile and malleable. They are found on the left-hand side of the periodic table. Generally, they have positive oxidation states. The metallic character decreases from left to right in a period and increases from top to bottom in a group. Nonmetals gain electrons and are poor conductors of heat and electricity. They are found on the right-hand side of the periodic table. Metalloids have properties intermediate between those of metals and nonmetals. They conduct electricity poorly. Atoms in the center of the periodic table tend to share electrons with other atoms. It is easier to gain or lose one electron than two electrons. Elements that lose one electron are generally more reactive than those that lose two electrons.
New perspectives on the nature and imaging of active site in small metallic particles: II. Electronic effects
Published in Chemical Engineering Communications, 2021
As elucidated above, the twin techniques of STM/STS spectroscopy are versatile tools for the characterization of surface electronic structure of semiconductors and metals, in terms of surface electronic band gaps (EBG). For sake of completeness, we now briefly illustrate further the concept of electronic band gap, and its sensitivity to parameters such as temperature, grain size, and presence of reactive gases. If the band gap is narrow, the electrons can easily transfer over to the conduction band (CB) as excitons; these materials are semiconductors. Elemental Si is an example of a narrow EBG semiconductor; its EBG value is of the order of 1–1.5 eV. It is extensively used in the manufacture of electronic circuits (IC circuits) and semiconductor chips/devices. For metals, there is no gap between the VB and CB; metals are therefore good conductors of electricity, but unable to participate in bond-breaking and bond-forming reactions. On the contrary, the EBG in non-metals is very large; the insulators are therefore unable to conduct electricity. The EBG of semiconductors tends to decrease as the temperature is increased. An increased interatomic distance in the lattice decreases the potential seen by the electrons; which reduces the size of the band gap. For example, the EBG of a semiconductor can be correlated to temperature, by the following empirical equation: where, α and β are fitting constants, in units of eV/K and K, respectively.