![]() Some elements have countries in their names (francium, polonium, and germanium), while others bear the names of notable scientists (einsteinium, nobelium, and curium). In addition to chemical properties, the periodic table reveals the cultural history of each element. We also will examine how these patterns allow us to predict the formation of compounds. In this unit, we will discuss some of those patterns, including electron configuration, size, and reactivity. In addition to the atomic number, there are many patterns within the periodic table. In fact, if the number of protons was to change, the atom’s identity would change. We can organize the periodic table this way because all atoms of a specific element have the same number of protons. This information was obtained from the International Union of Pure and Applied Chemistry (IUPAC) Web site: table is organized by atomic number, which is the number of protons in the nucleus. In the periodic table, shown on the following pages, elements in columns have similar properties, and elements so related (like sulfur, selenium, and tellurium) are members of the same group or family and are congeners of one another. Many simple chemical compounds are formed from a metal reacting with a nonmetal. All the metals have high conductivities for heat and electricity. Most of the metals are shiny, deformable solids, but mercury has such a low melting point that it is a liquid at room temperature. All the elements in the middle and left of the table are metals, except gaseous hydrogen (1). The elements to the upper right, above a diagonal line from aluminum (13) to polonium (84), are nonmetals, about half of which exist as gases under normal laboratory conditions. The lightest are at the top of the chart the atomic masses increase toward the bottom of the chart. The periodic table displays the pattern of properties of the elements. Thus, element 27 is cobalt (whose atomic number is 27), not aluminum (whose atomic mass is 27). When an element is referred to by an integer, this number means the atomic number, not the atomic mass. The atomic number, which appears above each element symbol, represents the meaningful order in the periodic table. Therefore, the order in the table cannot be based solely on atomic mass. Iodine resembles bromine because these elements are nonmetallic halogens that form compounds like those of chlorine. The chemical properties of tellurium are like those of selenium because both are semimetallic elements that form compounds like those of sulfur. (See Figure 2.)įigure 2. Comparing tellurium and iodine.Ĭonsider the proper placement of tellurium and iodine in the periodic table, as shown in Figure 2. Compare the atomic mass of tellurium (Te) to iodine (I). Notice that the elements also seem to be arranged in order of increasing atomic mass. In the preceding section, you reviewed the historical determination of atomic masses. The elements are arranged in order of increasing atomic number in horizontal rows called periods. Besides the element name and symbol, the atomic mass is at the bottom, and the atomic number is at the top. In the modern periodic table, each box contains four data, as shown in Figure 1. Each column contains a group of elements with similar chemical behavior. In each row, the atomic masses increase toward the right. (The inert gases had not been discovered at that time the correct values for similar properties are 8 and 18.) The periodic table is based on atomic masses and similar properties. He arranged all known chemical elements in order of their atomic masses and found that similar physical and chemical properties recurred every 7 elements for the lighter elements and every 17 elements for the heavier ones. ![]() In 1869, the Russian chemist Dmitri Mendeleyev published his great systematization called the periodic table. Quiz: Introduction to Oxidation-Reduction Reactions.Introduction to Oxidation-Reduction Reactions.Quiz: Heat Capacities and Transformations.Quiz: Introduction to Organic Compounds.Quiz: Compounds with Additional Elements.
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