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Periodic Table: Elements
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Reading The Periodic Table Evelyn Williams John Hope Community Academy 8125 South Shore Drive 5515 S. Lowe Ave. Chicago IL 60617 Chicago IL 60621 (312)734-1841 (312)535-3160 Objectives: This lesson is designed for 8th Grade students. Students will be able to: 1) Categorize a group of shells and unknown elements using different characteristics. 2) Read and interpret the Periodic Table. Materials Needed: 1. One set of assorted shells for each group. 2.
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The Structure of the Table The horizontal rows of the periodic chart are called periods or rows. There are seven periods, each of which begins with an atom having only one valence electron and ends with a complete outer shell structure of an inert gas. The first three periods are short periods consisting of 2, 8, and 8 elements respectively. Periods 4 and 5 are long periods of 18 each, while period 6 has 32 elements, and period 7 is incomplete with only 17 elements most of which are radioactive and do not occur in nature.
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For elements in groups labeled A in the periodic table (IA, IIA, etc.), the number of valence electrons corresponds to the group number. Thus Li, Na, and other elements in group IA have one valence electron. Be, Mg, and other group-IIA elements have two valence electrons. B, Al and other group-IIIA elements have three valence electrons, and so on. The row, or period, number that an element resides in on the table is equal to the number of total shells that contain electrons in the atom. H and He in the first period normally have electrons in only the first shell; Li, Be, B, and other period-two elements have two shells occupied, and so on. To write the electron configuration of elements, scientists often use a shorthand in which the element's symbol is followed by the element's electron shells, written as a right-hand parentheses symbol ")". The number of electrons in each shell is then written after the ) symbol.
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There are 18 vertical columns, or groups, in the standard periodic table. At present, there are three versions of the periodic table, each with its own unique column headings, in wide use. The three formats are the old International Union of Pure and Applied Chemistry (IUPAC) table, the Chemical Abstract Service (CAS) table, and the new IUPAC table. The old IUPAC system labeled columns with Roman numerals followed by either the letter A or B. Columns 1 through 7 were numbered IA through VIIA, columns 8 through 10 were labeled VIIIA, columns 11 through 17 were numbered IB through VIIB and column 18 was numbered VIII. The CAS system ... used Roman numerals followed by an A or B. This method, however, labeled columns 1 and 2 as IA and IIA, columns 3 through 7 as IIIB through VIB, column 8 through 10 as VIII, columns 11 and 12 as IB and IIB and columns 13 through 18 as IIIA through VIIIA. However, in the old IUPAC system the letters A and B were designated to the left and right part of the table, while in the CAS system the letters A and B were designated to the main group elements and transition elements respectively.
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A necessary prerequisite to the construction of the periodic table was the discovery of the individual elements. Although elements such as gold, silver, tin, copper, lead and mercury have been known since antiquity, the first scientific discovery of an element occurred in 1649 when Hennig Brand discovered phosphorous. During the next 200 years, a vast body of knowledge concerning the properties of elements and their compounds was acquired by chemists (view a 1790 article on the elements). By 1869, a total of 63 elements had been discovered. As the number of known elements grew, scientists began to recognize patterns in properties and began to develop classification schemes.
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The alkali metals are located in Group IA (first column) of the periodic table. Sodium and potassium are examples of these elements. Alkali metals form salts and many other compounds. These elements are less dense than other metals, form ions with a +1 charge, and have the largest atom sizes of elements in their periods. The alkali metals are highly reactive.
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