China
Africa
Explore chapters and articles related to this topic
Chemical Reactions
Published in John Bird, Newnes Engineering Science Pocket Book, 2012
To represent a reaction a chemical shorthand is used. A symbol represents an element (such as H for hydrogen, O for oxygen, Cu for copper, Zn for zinc, and so on) and a formula represents a compound and gives the type and number of elements in the compound. For example, one molecule of sulphuric acid, H2SO4, contains 2 atoms of hydrogen, 1 atom of sulphur and 4 atoms of oxygen. Similarly, a molecule of methane gas, CH4, contains 1 atom of carbon and 4 atoms of hydrogen.
Cells and batteries
Published in Adrian Waygood, An Introduction to Electrical Science, 2013
A chemical symbol is used to identify a particular element. For example, the symbol H represents hydrogen, Zn represents zinc, and so on. Combinations of these symbols represent compounds, with numeric subscripts indicating the presence of two or more atoms of an element. For example, the chemical symbol for (the compound) water, is H2O, which indicates a molecule comprising two atoms of hydrogen and one atom of oxygen.
Printed Warning Signs, Tags, and Labels
Published in Waldemar Karwowski, Anna Szopa, Marcelo M. Soares, Handbook of Standards and Guidelines in Human Factors and Ergonomics, 2021
The safety symbol is defined as an image—with or without a surrounding geometrical shape—that conveys a message without the use of words. The surrounding geometrical shape is defined as the surround shape and is usually a square or a circle.
Atomistic Study on the Energetic and Mechanical Behaviors of Helium Bubble Nucleation and Growth in RAFM Steel
Published in Fusion Science and Technology, 2022
Shouhua Sun, Jingyi Shi, Liuliu Li, Lei Peng
The formation energy calculated by Eq. (1) for each HenVm cluster with the lowest-energy configuration is analyzed. According to the dependence on the number of vacancies, the formation energy of HenVm clusters containing 1 to 20 helium atoms is plotted in Fig. 1. To avoid excessive data point overlap, Fig. 1 is divided into Figs. 1a and 1b. Figure 1a is used to characterize the formation energy of HenVm clusters with the number of helium atoms smaller than 11. Figure 1b is for HenVm clusters with the number of helium atoms larger than 11. The formation energy of the HenV11 cluster is included in Figs. 1a and 1b for comparison. The HenVm clusters with the same number of helium atoms are indicated by the same symbol and color and in the same curve. All curves have a similar trend; i.e., the lowest point of the curve occurs when the number of the helium atom and the vacancy are the same. This indicates that there exists an optimal He/V ratio during the binding of vacancies to the HenVm clusters to prompt the growth of clusters. The optimal ratio is consistent for all clusters with different helium atoms and appears as 1.0.
Chemical and other aspects of Rutherford’s nuclear atom
Published in Journal of the Royal Society of New Zealand, 2021
Although Rutherford did not refer to H-3 in his early works, in his Bakerian Lecture of 1920 he predicted the existence of another mass-3 isotope, namely He-3 consisting of three protons and one electron (or two protons and one neutron). As mentioned, he chose the symbol for the nucleus of the hypothetical helium isotope. Rutherford (1920, p. 394) now believed to have found evidence in his alpha collision experiments of ‘atoms of mass 3 carrying two positive charges … [and with] physical and chemical properties very nearly identical with those of helium’. He suggested that the He-3 isotope might be detected by means of the shift in its spectral lines, such as originally proposed by Bohr. Not only did Rutherford believe to have found He-3, he also found it ‘very likely that one electron can also bind two H nuclei and possibly also one H nucleus’, which in the first case would be ‘an isotope of hydrogen’ (Rutherford 1920, p. 396). Rutherford had considered the possibility of a mass-2 particle already in the experiments with alpha particles colliding with nitrogen, but without elaborating or commenting on their nature. On 10 January 1918 he entered in his notebook: ‘Suppose long-range scintillations in are due to atom charge + e and mass M = 2 called x’ (Rutherford 1919, p. 586; Feather 1940, p. 152).
Technetium-99m metastable radiochemistry for pharmaceutical applications: old chemistry for new products
Published in Journal of Coordination Chemistry, 2019
Bianca Costa, Derya Ilem-Özdemir, Ralph Santos-Oliveira
The chemical element technetium whose symbol is Tc has atomic number 43 and is located in group 7 (7B) of the periodic table. All isotopes of technetium are radioactive. The two most prevalent isotopes are 99mTc formed from the decay of 99Mo and 99Tc, the decay product of 99mTc. 99Tc (βmax: 274 keV) is a significant by-product of U-235 fission (6% thermal neutron yield). With a half-life of 2.1 × 105 years, 99Tc can build up in the environment and can be obtained in macroscopic quantities. In the metallic form, 99Tc is a transition metal, silvery gray. Like the other transition metals, 99Tc presents peculiar properties, such as varied colors, various oxidation numbers and different coordination numbers, which result from the existence of a sub-level “d” partially filled in the valence layer [11].