{"id":69,"date":"2017-08-18T08:54:51","date_gmt":"2017-08-18T08:54:51","guid":{"rendered":"http:\/\/americanboard.org\/Subjects\/chemistry\/?page_id=69"},"modified":"2020-12-29T08:37:14","modified_gmt":"2020-12-29T08:37:14","slug":"the-periodic-table","status":"publish","type":"page","link":"https:\/\/americanboard.org\/Subjects\/chemistry\/the-periodic-table\/","title":{"rendered":"The Periodic Table"},"content":{"rendered":"
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\u2b05 Previous Lesson<\/a>\u00a0Workshop Index<\/a>\u00a0Next Lesson \u27a1<\/a><\/p>\n<\/div>\n

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Atomic Structure, Periodicity, and Matter:The Periodic Table<\/h1>\n

Objective<\/h4>\n

In this lesson we will discuss a brief history of the development of the periodic table, and how to use the modern periodic table to obtain information about the atoms of the known elements.<\/p>\n

Previously we covered…<\/h4>\n
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  • Introducing the parts of the atom<\/li>\n
  • The structure of the nucleus including protons and neutrons<\/li>\n
  • Understanding the mass spectrograph<\/li>\n
  • Calculating atomic mass<\/li>\n
  • Electrons and electron configuration<\/li>\n<\/ul>\n
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    History<\/h3>\n

    By the early-1800s, approximately 60 elements had been discovered, and chemists were overwhelmed with the task of categorizing the properties of so many new elements. There was no method for accurately determining atomic masses, and chemists used different mass numbers in their work, making the results of one chemist’s work difficult, if not impossible, to be interpreted by another. What was needed was a standardized method for determining atomic mass, and a system of classification of the elements grouping them by similarities.<\/p>\n

    A number of chemists began to observe relationships among the properties of certain elements. One of the earliest attempts to organize the elements based on their chemical and physical properties was made by the German chemist, Johann Dobereiner. He observed that certain elements could be grouped together in threes based on their similarities. One example was calcium, strontium, and barium; another group was chlorine, bromine, and iodine. In each group, the atomic weight of the middle element was the approximate average of the atomic weights of the other two elements. The grouping of elements into triads appeared to Dobereiner to be more than a mere coincidence, and he developed the law of triads<\/abbr> from 1817 to 1829.<\/p>\n

    From 1863 to 1865, English chemist John Newlands found that when the elements were arranged according to increasing atomic mass, there was a repeating pattern relating to the chemical properties of the elements. Beginning with hydrogen, he observed that every eighth element had similar properties. Because an octave is a group of musical notes that repeats every eighth note, Newlands named his discovery the law of octaves<\/abbr>. The law of octaves was not readily accepted because it did not work for all of the known elements. In addition, Newlands was criticized for his analogy of elements to musical notes by fellow scientists who thought it to be unscientific.<\/p>\n

    Development of the Periodic Table<\/h3>\n

    As the result of the Karlsruhe Conference held in Germany in 1860, the atomic masses used by chemists throughout the world were standardized. Using the standards from the conference, the Russian chemist, Dimitri Mendeleev, created a table of the 60 elements<\/abbr> known at the time by arranging them by increasing atomic mass. When organized this way he noticed the periodic pattern in their properties and formulated the periodic law<\/abbr>. However, his procedure left several empty spaces in his periodic table. Undaunted, he predicted the existence, as well as the properties, of the unknown elements that would be found to fill these spaces. Mendeleev’s predictions were proven to be correct with the discoveries of scandium, gallium, and germanium.<\/p>\n

    Mendeleev\u2019s periodic table was not completely accurate, and new discoveries indicated that several of the elements in his table were not in the correct order. In 1913, the English chemist Henry Moseley found that by arranging the elements in the periodic table by atomic number rather than atomic mass, the problems with the order of the elements was resolved.<\/p>\n

    Mendeleev is generally credited with the production of the first periodic table<\/abbr>, but it was hardly a solo effort. Many scientists contributed, and there is even some disagreement concerning who deserves credit for being the “father” of the periodic table. Mendeleev and German chemist Lothar Meyer, working independently of one another, both produced remarkably similar results concerning the periodic nature of the elements. Unfortunately for Meyer, Mendeleev’s table was published first in 1869 and Meyer’s not until 1870.<\/p>\n

    Other major changes to the periodic table resulted from the work of American chemist Glenn Seaborg in the 1940’s. He and his colleagues discovered plutonium and the transuranium elements<\/abbr> through element 102. In addition, he identified over 100 previously unknown isotopes which increased the accuracy of the atomic masses of the elements. Dr. Seaborg received the Nobel Prize for Chemistry in 1951, and was further honored by having element 106 (Seaborgium) named in his honor, the only element named for a living chemist. Seaborg was also responsible for the fact that, in the modern table, the elements lanthanum and actinium are no longer found in the Lanthanide<\/abbr> and Actinide series<\/abbr> of elements. His work established these elements to be closer in nature to the transition<\/abbr> elements than to the inner transition<\/abbr> or rare earth<\/abbr> elements.<\/p>\n

    The Modern Periodic Table<\/h3>\n

    The periodic table has gone through many modifications since the time of Mendeleev. Significant changes include the rearrangement of the elements by atomic number rather than atomic mass, inclusion of the noble gases, and the addition of more than 40 newly discovered or created elements. However, the basic structure of the periodic table has survived, and every known element today can be placed in the periodic table in a group of elements with similar properties.<\/p>\n

    \"the<\/center>The modern periodic table is a mosaic of elements pieced together in a particular order to create a picture that can be used as a convenient reference tool by chemists. Like all mosaics, the periodic table is made of \u2018tiles\u2019. Below is a \u2018tile\u2019 from a periodic table representing the element calcium. The amount and arrangement of information contained in each element\u2019s square varies from table to table, but this is a typical example.<\/p>\n

    \"Example<\/center>In addition to element names and symbols, the structure of the atoms for each element can be determined from each tile. The atomic number, by definition, is the number of protons in an atom of an element, and in a neutral atom the number of electrons will be the same as the number of protons. Often a column of small numbers will be included for each element that indicates the arrangement of the electrons. The atomic mass is the weighted average of the masses of the natural isotopes of the element, and since it an average; it is expressed as a whole number with a decimal fraction. The number of neutrons in an atom of an element can be easily determined by rounding off the atomic mass to the nearest whole number mass number<\/abbr> and subtracting the atomic number from it.<\/p>\n

    The horizontal rows of the periodic table are called periods<\/abbr> and the vertical columns which contain elements with similar chemical and physical properties are called families<\/abbr> (or groups). This arrangement forms regions in the table that contain elements that are classified as: metals<\/abbr>, nonmetals<\/abbr>, and metalloids<\/abbr> or semimetals.<\/p>\n

    It is important to note here that there are many forms of the periodic table conveying specialized information about each element. Therefore, you may find slightly different periodic tables than the one shown above in textbooks and on the internet.<\/p>\n

    Elements of the Periodic Table: The Metals<\/h3>\n

    \"Periodic<\/center><\/p>\n

    Metals shown in dark green<\/p>\n

    The majority of the elements are metals. They are generally grouped on the left side of the periodic table. Metals are usually shiny, solid at room temperature, good conductors of heat and electricity, malleable and ductile. The metals can be divided into five subgroups: alkali metals, alkaline earth metals, transition metals, post-transition metals, and inner transition metals.<\/p>\n

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    \"Periodic<\/p>\n

    Alkali metals<\/strong> shown in yellow<\/p>\n<\/div>\n

    Group 1 elements except for hydrogen are known as alkali metals<\/abbr>. These metals get their name because they react with water to form alkaline or basic solutions. Since the alkali metals are highly reactive, they are never found as elements in nature, but they are always found bonded to other elements. These metals have atoms with only one s<\/em> electron in their outermost energy level and readily lose that electron in forming ionic chemical bonds<\/abbr> with non-metallic elements. The alkali metals form ions with a +1 charge in these bonds. The alkali metals are soft metals, and have low melting points. They react so vigorously with oxygen and water that they are usually stored in oil or kerosene to protect them from the oxygen and moisture in the air.<\/p>\n

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    \"Periodic<\/p>\n

    Alkaline earth<\/strong> metals shown in light green<\/p>\n<\/div>\n

    Alkaline earth metals<\/abbr> are found in group 2, and also form basic solutions when they react with water. The alkaline earth metals have two electrons in their outermost energy level, completing the s<\/em> energy sublevel and giving them a little more stability in the metallic state than the alkalis. This group forms ionic bonds by losing their two outermost electrons and forming a cation<\/abbr> with a +2 charge when bonding with nonmetals. The alkaline earth metals are harder than the alkali metals. They have a gray-white luster that tarnishes quickly in air as the surface oxidizes. Alloys of these metals can be used as low density structural materials.<\/p>\n

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    \"Periodic<\/p>\n

    Transition<\/strong> metals shown in green<\/p>\n<\/div>\n

    The transition metals<\/abbr><\/strong> are found in the middle of the periodic chart occupying groups 3 through 12 (or on some tables the groups designated with a B). As with all metals, the transition metals are good conductors of heat and electricity, malleable, and ductile. With the exception of liquid mercury (Hg), the transition metals are hard solids with relatively high melting and boiling points. This area of the periodic table is also called the d-block<\/em> because most of these elements have an incomplete d<\/em> sublevel.<\/p>\n

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    \"Periodic<\/p>\n

    Post-transition <\/strong>metals shown in blue<\/p>\n<\/div>\n

    There are a few metals located between the transition metals and the nonmetals in groups 13, 14, and 15 arranged in a stair step pattern. The metals are sometimes referred to as post-transition metals<\/abbr>. Included in this group are aluminum (Al), gallium (Ga), indium (In), tin (Sn), thallium (Tl), lead (Pb), and bismuth (Bi). These metals tend to have melting and boiling points that are lower than the transition metals and they are generally softer. Their outermost electrons fall into the p-block<\/em>.<\/p>\n<\/div>\n

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    \"Periodic<\/p>\n

    Inner transition <\/strong>metals shown in purple<\/p>\n<\/div>\n

    The inner transition metals<\/abbr> (rare earths) contain two groups, the lanthanide series<\/abbr> and the actinide<\/abbr> series<\/abbr>. These elements are usually found along the bottom of the periodic table. The lanthanides are metals with relatively high melting points. They are found mixed together in nature and are difficult to separate because their properties are so similar. The actinides are all radioactive. Only three of these elements are found in nature, and the rest are man-made elements known as transuranium elements. With the exception of plutonium-239, most transuranium elements decay quickly. These elements have a complicated chemistry because they generally contain three incomplete electron energy levels, f<\/em>, d<\/em>, and p<\/em>. On the periodic table they fall into what is also known as the f-block<\/em>.<\/p>\n<\/div>\n

    Elements of the Periodic Table: The Metalloids and Non-metals<\/h3>\n
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    \"Periodic<\/p>\n

    Metalloids <\/strong>are <\/strong> shown in gold<\/p>\n<\/div>\n

    The metalloids<\/abbr> are found on the periodic table in a stair-step configuration between the metallic elements and the nonmetals. Sometimes called the semimetals, these elements have the physical and chemical properties of both metals and nonmetals and are semiconductors. Silicon and germanium are the two best known metalloids, since they are used in the production of transistors, computer chips, and solar cells.<\/p>\n

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    \"Periodic<\/p>\n

    Nonmetals <\/strong>are <\/strong> shown in orange<\/p>\n<\/div>\n

    Nonmetals<\/abbr> are located on the upper right side of the periodic table, except for the nonmetal hydrogen. Other than bromine which is a liquid at room temperature, nonmetals are primarily gases, brittle solids, or crystalline solids. They are generally poor conductors of heat and electricity with varying chemical reactivity. Nonmetals gain electrons when they react with metals and form anions<\/abbr> (negative ions) in ionic bonds. Unlike metals, nonmetals will react with other nonmetals by sharing electrons and forming covalent<\/abbr> bonds<\/abbr>.<\/p>\n<\/div>\n

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    \"Periodic<\/p>\n

    Halogens<\/strong> are shown in red<\/p>\n<\/div>\n

    The nonmetals found in group 17 are called halogens<\/abbr>. Chemically these are highly active elements which are never found free in nature. The halogens all have 7 electrons in the outermost energy level (p<\/em> sublevel) and all are extremely aggressive in finding electrons to complete the stable octet which gives each halide ion the configuration of a noble gas. The halogen family elements exist in all three states: F and Cl are gases at room temperature, Br is the only liquid nonmetal, and iodine is a solid.<\/p>\n<\/div>\n

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    \"Periodic<\/p>\n

    Noble gases<\/strong> are shown in pink<\/p>\n<\/div>\n

    The elements in group 18 are commonly called the noble gases<\/abbr>. The former designation for this group was inert gases because they were thought to be completely inactive chemically. Some of the larger noble gases have been forced into compounds which are very unstable but which prompted the name change. This group has eight electrons in the outermost energy level (completed s <\/em>and p<\/em> energy sublevels) which is the point of most stability for the atoms.<\/p>\n<\/div>\n

    Review of the Periodic Table<\/h3>\n

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