![]() Bromine is the only nonmetal that is a liquid at room temperature. Others, such as carbon, sulfur, phosphorus, and iodine, are brittle solids. At room temperature, several nonmetals, including oxygen, nitrogen, fluorine, and chlorine, are gases. For example, nonmetals generally are poor conductors of heat and electricity. Except for mercury (a liquid at room temperature), all the metallic elements are solids at room temperature.Įlements to the right of the stepped line are nonmetals, elements that lack metallic properties. Most metals are malleable, which means they can be hammered into thin sheets or foil, and ductile, meaning they can be drawn into wires. Metals have a characteristic luster and are generally good conductors of heat and electricity. Except for hydrogen, those elements to the left of this line are metals. Who arranged the elements according to atomic mass series#The two 14-element series are called the lanthanide series (atomic numbers 58≧1) and the actinide series (90≡03).Įlements are divided into two main classes by the heavy, stepped gray line shown in Figure 2.5. By extracting a 14-element series from the sixth and seventh periods and listing these two series separately at the bottom of the table, we can use a more compact form that limits the width of the table to 18 elements. If all the elements were included in the periodic table, it would have to be quite wide to accommodate the periods containing 32 elements, and there would be a large blank space above these long periods. A number at the left of the row identifies each period. The periods vary in length from two elements (the first period) to 32 elements (the sixth and seventh periods). Periods are the horizontal rows of elements. We place a group number (for example, 1A, 2A, 3B, and so on) at the top of each column. Groups, or families, are the vertical columns of elements that have similar properties. The periodic table is divided into groups and periods. The elements are placed in order of increasing atomic number, a property more responsible for the behavior of an element than is its atomic mass. Each box, or entry, in the table gives the chemical symbol, atomic number ( Z), and atomic mass of an element (illustrated for iron). There are more than 110 elements listed in the modern periodic table shown in Figure 2.5. The predictive nature of Mendeleev's periodic table led to its wide acceptance as a tremendous scientific accomplishment. Table 2.2 shows just how accurate his predictions were, when compared to the properties of the actual element germanium discovered 15 years later. For example, he left a blank space for an undiscovered element that he called "eka-silicon" and used its location between silicon and tin to predict an atomic weight of 72 and other properties. Furthermore, because the table was based on patterns of properties, he was able to predict some properties of the missing elements. Instead of seeing these gaps as defects, he boldly predicted the existence of undiscovered elements to fill the gaps. When Mendeleev placed elements with similar properties in the same vertical group, a few gaps were created in his table. For example, he correctly placed tellurium (atomic weight 127.6) ahead of iodine (atomic weight 126.9) so that tellurium would be in the same column as the similar elements sulfur and selenium. So that there would be no exceptions to the principle that all the elements in a group display similar properties, Mendeleev placed some elements out of order, that is, not in the strict order of increasing atomic weight. This group similarity recurs periodically, hence the name periodic table. In this arrangement, elements that most closely resemble one another in physical and chemical properties tend to fall in the same vertical group. Mendeleev arranged the elements in order of increasing atomic weight, from left to right in rows and from top to bottom in columns (or groups). For now, though, we will deduce a few ideas from it to help us name and write formulas of chemical compounds. The periodic table is so important that we will devote most of Chapter 8 to it, and it is a recurring theme in Chapters 20, 21, and 22. In its modern form, the periodic table organizes a vast array of chemical knowledge. Dmitri Mendeleev published the first successful arrangement, called a periodic table, in 1869. One way to do this was to arrange the elements in a manner that would establish categories of elements having similar physical and chemical properties. Chemists badly needed a way to organize the growing collection of chemical data. By 1830, 55 elements were recognized, but there was no apparent pattern in their properties. In the nineteenth century, chemists discovered dozens of new elements. 2.5 The Periodic Table: Elements Organized ![]()
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