Metals are lustrous, good conductors of electricity, and readily shaped (they are ductile and malleable), whereas solid nonmetals are generally brittle and poor electrical conductors. They are separated by a diagonal band of semimetals. Metals are located on the left of the periodic table, and nonmetals are located on the upper right. Semimetals exhibit properties intermediate between those of metals and nonmetals. The elements can be broadly divided into metals, nonmetals, and semimetals. Some of the groups have widely-used common names, including the alkali metals (Group 1) and the alkaline earth metals (Group 2) on the far left, and the halogens (Group 17) and the noble gases (Group 18) on the far right. Elements that exhibit similar chemistry appear in vertical columns called groups (numbered 1–18 from left to right) the seven horizontal rows are called periods. The periodic table is an arrangement of the elements in order of increasing atomic number. The periodic table is used as a predictive tool. As expected, semimetals exhibit properties intermediate between metals and nonmetals. Most solid nonmetals are brittle, so they break into small pieces when hit with a hammer or pulled into a wire. Nonmetals can be gases (such as chlorine), liquids (such as bromine), or solids (such as iodine) at room temperature and pressure. Nonmetals, in contrast, are generally poor conductors of heat and electricity and are not lustrous. Of the metals, only mercury is a liquid at room temperature and pressure all the rest are solids. The vast majority of the known elements are metals. Metals-such as copper or gold-are good conductors of electricity and heat they can be pulled into wires because they are ductile they can be hammered or pressed into thin sheets or foils because they are malleable and most have a shiny appearance, so they are lustrous. The distinction between metals and nonmetals is one of the most fundamental in chemistry. Gold-colored lements that lie along the diagonal line exhibit properties intermediate between metals and nonmetals they are called semimetals. The heavy orange zigzag line running diagonally from the upper left to the lower right through groups 13–16 in Figure 2.5.1 divides the elements into metals (in blue, below and to the left of the line) and nonmetals (in bronze, above and to the right of the line). The two rows of 14 elements at the bottom of the periodic table are the lanthanides and the actinides, whose positions in the periodic table are indicated in group 3. Groups 3–12 are in the middle of the periodic table and are the transition elements, listed as B in older tables. Groups 1, 2, and 13–18 are the main group elements, listed as A in older tables. The elements are stacked in such a way that elements with similar chemical properties form vertical columns, called groups, numbered from 1 to 18 (older periodic tables use a system based on roman numerals). The rows are called periods, and they are numbered from 1 to 7. The elements are arranged in seven horizontal rows, in order of increasing atomic number from left to right and top to bottom. It summarizes huge amounts of information about the elements in a way that facilitates the prediction of many of their properties and chemical reactions. The elements are arranged in a periodic table, which is probably the single most important learning aid in chemistry. The semimetals lie along a diagonal line separating the metals and nonmetals. The metals are on the bottom left in the periodic table, and the nonmetals are at the top right. In a neutral atom, the number of electrons equals the number of protons.įigure 2.5.1: The Periodic Table Showing the Elements in Order of Increasing Z. The chemistry of each element is determined by its number of protons and electrons. The names of the elements are listed in the periodic table, along with their symbols, atomic numbers, and atomic masses. Each element is assigned a unique one-, two-, or three-letter symbol. The rationale for the peculiar format of the periodic table is explained later. The known elements are arranged in order of increasing Z in the periodic table ( Figure 2.5.1). The atomic number is therefore different for each element. The identity of an element is defined by its atomic number (Z), the number of protons in the nucleus of an atom of the element. Rutherford’s nuclear model of the atom helped explain why atoms of different elements exhibit different chemical behavior. To become familiar with the organization of the periodic table.
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