{"id":387,"date":"2016-01-11T20:00:16","date_gmt":"2016-01-11T20:00:16","guid":{"rendered":"https:\/\/opentextbc.ca\/introductorychemistryclone\/chapter\/electronic-structure-and-the-periodic-table-2\/"},"modified":"2020-07-28T19:09:33","modified_gmt":"2020-07-28T19:09:33","slug":"electronic-structure-and-the-periodic-table","status":"publish","type":"chapter","link":"https:\/\/opentextbc.ca\/introductorychemistryclone\/chapter\/electronic-structure-and-the-periodic-table\/","title":{"raw":"Electronic Structure and the Periodic Table","rendered":"Electronic Structure and the Periodic Table"},"content":{"raw":"[latexpage]\r\n
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Learning Objectives<\/p>\r\n\r\n<\/header>\r\n

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  1. Relate the electron configurations of the elements to the shape of the periodic table.<\/li>\r\n \t
  2. Determine the expected electron configuration of an element by its place on the periodic table.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\nIn Chapter 3: Atoms, Molecules, and Ions<\/a>, we introduced the periodic table as a tool for organizing the known chemical elements. A periodic table is shown in Figure 8.5 \"The Periodic Table.\" The elements are listed by atomic number (the number of protons in the nucleus), and elements with similar chemical properties are grouped together in columns.\r\n\r\n[caption id=\"attachment_118\" align=\"aligncenter\" width=\"600\"]\"The<\/a> Figure 8.5 \"The Periodic Table.\" View an accessible periodic table online<\/a>.[\/caption]\r\n\r\nWhy does the periodic table have the structure it does? The answer is rather simple, if you understand electron configurations: the shape of the periodic table mimics the filling of the subshells with electrons<\/i>.\r\n\r\nLet us start with H and He. Their electron configurations are 1s<\/i>1<\/sup> and 1s<\/i>2<\/sup>, respectively; with He, the n<\/i> = 1 shell is filled. These two elements make up the first row of the periodic table (see Figure 8.6 \"The 1s<\/em> Subshell\").\r\n\r\n[caption id=\"attachment_376\" align=\"aligncenter\" width=\"600\"]\"The<\/a> Figure 8.6 \"The 1s<\/em> Subshell.\" H and He represent the filling of the 1s<\/em> subshell.[\/caption]\r\n\r\nThe next two electrons, for Li and Be, would go into the 2s<\/i> subshell. Figure 8.7 \"The 2s<\/i> Subshell\" shows that these two elements are adjacent on the periodic table.\r\n\r\n[caption id=\"attachment_377\" align=\"aligncenter\" width=\"600\"]\"The<\/a> Figure 8.7 \"The 2s<\/em> Subshell.\" In Li and Be, the 2s<\/em> subshell is being filled.[\/caption]\r\n\r\nFor the next six elements, the 2p<\/i> subshell is being occupied with electrons. On the right side of the periodic table, these six elements (B through Ne) are grouped together (Figure 8.14 \"The 2p<\/i> Subshell\").\r\n\r\n[caption id=\"attachment_378\" align=\"aligncenter\" width=\"600\"]\"The<\/a> Figure 8.8 \"The 2p<\/em> Subshell.\" For B through Ne, the 2p<\/em> subshell is being occupied.[\/caption]\r\n\r\nThe next subshell to be filled is the 3s<\/i> subshell. The elements when this subshell is being filled, Na and Mg, are back on the left side of the periodic table (Figure 8.9 \"The 3s<\/i> Subshell\").\r\n\r\n[caption id=\"attachment_379\" align=\"aligncenter\" width=\"600\"]\"The<\/a> Figure 8.9 \"The 3s<\/em> Subshell.\" Now the 3s<\/em> subshell is being occupied.[\/caption]\r\n\r\nNext, the 3p<\/i> subshell is filled with the next six elements (Figure 8.10 \"The 3p<\/i> Subshell\").\r\n\r\n[caption id=\"attachment_380\" align=\"aligncenter\" width=\"600\"]\"The<\/a> Figure 8.10 \"The 3p<\/em> Subshell.\" Next, the 3p<\/em> subshell is filled with electrons.[\/caption]\r\n\r\nInstead of filling the 3d<\/i> subshell next, electrons go into the 4s<\/i> subshell, which consists of K and Ca (Figure 8.11 \"The 4s<\/i> Subshell\").\r\n
    \r\n\r\n[caption id=\"attachment_381\" align=\"aligncenter\" width=\"600\"]\"The<\/a> Figure 8.11 \"The 4s<\/em> Subshell.\" The 4s<\/em> subshell is filled before the 3d<\/em> subshell. This is reflected in the structure of the periodic table.[\/caption]\r\n\r\nAfter the 4s<\/i> subshell is filled, the 3d<\/i> subshell is filled with up to 10 electrons. This explains the section of 10 elements in the middle of the periodic table, which consists of Sc to Zn (Figure 8.12 \"The 3d<\/i> Subshell\").\r\n
    \r\n\r\n[caption id=\"attachment_382\" align=\"aligncenter\" width=\"600\"]\"The<\/a> Figure 8.12 \"The 3d<\/em> Subshell.\" The 3d<\/em> subshell is filled in the middle section of the periodic table.[\/caption]\r\n\r\nAnd so forth. As we go across the rows of the periodic table, the overall shape of the table outlines how the electrons are occupying the shells and subshells.\r\n\r\nThe first two columns on the left side of the periodic table are where the s<\/i> subshells are being occupied. Because of this, the first two columns of the periodic table are labelled the <\/i>[pb_glossary id=\"1738\"]s<\/i> block[\/pb_glossary]. Similarly, the <\/i>[pb_glossary id=\"1740\"]p<\/i> block[\/pb_glossary]\u00a0are the right-most six columns of the periodic table, the <\/i>[pb_glossary id=\"1741\"]d<\/i> block[\/pb_glossary]\u00a0is the middle 10 columns of the periodic table, while the <\/i>[pb_glossary id=\"1742\"]f<\/i> block[\/pb_glossary]\u00a0is the 14-column section that is normally depicted as detached from the main body of the periodic table. It could be part of the main body, but then the periodic table would be rather long and cumbersome. Figure 8.13 \"Blocks on the Periodic Table\" shows the blocks of the periodic table.\r\n
    \r\n\r\n[caption id=\"attachment_383\" align=\"aligncenter\" width=\"600\"]\"The<\/a> Figure 8.13 \"Blocks on the Periodic Table.\" The periodic table is separated into blocks depending on which subshell is being filled for the atoms that belong in that section.[\/caption]\r\n\r\nThe electrons in the highest-numbered shell, plus any electrons in the last unfilled subshell, are called [pb_glossary id=\"1746\"]valence electrons[\/pb_glossary]; the highest-numbered shell is called the [pb_glossary id=\"1747\"]valence shell[\/pb_glossary]. (The inner electrons are called core electrons<\/i>.) The valence electrons largely control the chemistry of an atom. If we look at just the valence shell\u2019s electron configuration, we find that in each column, the valence shell\u2019s electron configuration is the same. For example, take the elements in the first column of the periodic table: H, Li, Na, K, Rb, and Cs. Their electron configurations (abbreviated for the larger atoms) are as follows, with the valence shell electron configuration highlighted:\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n
    Table 8.1 Electron Configurations of Elements in the First Column of the Periodic Table<\/caption>\r\n
    Element<\/th>\r\nElectron Configuration<\/th>\r\n<\/tr>\r\n
    H<\/td>\r\n1s<\/em>1<\/sup><\/td>\r\n<\/tr>\r\n
    Li<\/td>\r\n1s<\/em>2<\/sup>2s<\/em>1<\/sup><\/td>\r\n<\/tr>\r\n
    Na<\/td>\r\n[Ne]3s<\/em>1<\/sup><\/td>\r\n<\/tr>\r\n
    K<\/td>\r\n[Ar]4s<\/em>1<\/sup><\/td>\r\n<\/tr>\r\n
    Rb<\/td>\r\n[Kr]5s<\/em>1<\/sup><\/td>\r\n<\/tr>\r\n
    Cs<\/td>\r\n[Xe]6s<\/em>1<\/sup><\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\nThey all have a similar electron configuration in their valence shells: a single s<\/i> electron. Because much of the chemistry of an element is influenced by valence electrons, we would expect that these elements would have similar chemistry \u2014 and they do<\/em>. The organization of electrons in atoms explains not only the shape of the periodic table but also the fact that elements in the same column of the periodic table have similar chemistry.\r\n\r\nThe same concept applies to the other columns of the periodic table. Elements in each column have the same valence shell electron configurations, and the elements have some similar chemical properties. This is strictly true for all elements in the s<\/i> and p<\/i> blocks. In the d<\/i> and f<\/i> blocks, because there are exceptions to the order of filling of subshells with electrons, similar valence shells are not absolute in these blocks. However, many similarities do exist in these blocks, so a similarity in chemical properties is expected.\r\n\r\nSimilarity of valence shell electron configuration implies that we can determine the electron configuration of an atom solely by its position on the periodic table. Consider Se, as shown in Figure 8.14 \"Selenium on the Periodic Table.\" It is in the fourth column of the p<\/i> block. This means that its electron configuration should end in a p<\/i>4<\/sup> electron configuration. Indeed, the electron configuration of Se is [Ar]4s<\/i>2<\/sup>3d<\/i>10<\/sup>4p<\/i>4<\/sup>, as expected.\r\n\r\n[caption id=\"attachment_384\" align=\"aligncenter\" width=\"600\"]\"Selenium<\/a> Figure 8.14 \"Selenium on the Periodic Table.\"[\/caption]\r\n\r\n
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    Example 8.5<\/p>\r\n\r\n<\/header>\r\n

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    Problem<\/h1>\r\nFrom the element\u2019s position on the periodic table, predict the valence shell electron configuration for each atom. See Figure 8.15 \"Various Elements on the Periodic Table.\"\r\n
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    1. Ca<\/li>\r\n \t
    2. Sn<\/li>\r\n<\/ol>\r\n

      Solution<\/h2>\r\n
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      1. Ca is located in the second column of the s<\/i> block. We would expect that its electron configuration should end with s<\/i>2<\/sup>. Calcium\u2019s electron configuration is [Ar]4s<\/i>2<\/sup>.<\/li>\r\n \t
      2. Sn is located in the second column of the p<\/i> block, so we expect that its electron configuration would end in p<\/i>2<\/sup>. Tin\u2019s electron configuration is [Kr]5s<\/i>2<\/sup>4d<\/i>10<\/sup>5p<\/i>2<\/sup>.<\/li>\r\n<\/ol>\r\n

        Test Yourself<\/h1>\r\nFrom the element\u2019s position on the periodic table, predict the valence shell electron configuration for each atom. See\u00a0Figure 8.15 \"Various Elements on the Periodic Table.\"\r\n
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        1. Ti<\/li>\r\n \t
        2. Cl<\/li>\r\n<\/ol>\r\n

          Answer<\/h2>\r\n
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          1. [Ar]4s<\/i>2<\/sup>3d<\/i>2<\/sup><\/li>\r\n \t
          2. [Ne]3s<\/i>2<\/sup>3p<\/i>5<\/sup><\/li>\r\n<\/ol>\r\n[caption id=\"attachment_385\" align=\"aligncenter\" width=\"600\"]\"Varius<\/a> Figure 8.15 \"Various Elements on the Periodic Table.\" [Long Description]<\/a>[\/caption]<\/div>\r\n<\/div>\r\n
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            Food and Drink App: Artificial Colours<\/h1>\r\nThe colour of objects comes from a different mechanism than the colours of neon and other discharge lights. Although coloured lights produce their colours, objects are coloured because they preferentially reflect a certain colour from the white light that shines on them. A red tomato, for example, is bright red because it reflects red light while absorbing all the other colours of the rainbow.\r\n\r\nMany foods, such as tomatoes, are highly coloured; in fact, the common statement \u201cyou eat with your eyes first\u201d is an implicit recognition that the visual appeal of food is just as important as its taste. But what about processed foods?\r\n\r\nMany processed foods have food colourings added to them. There are two types of food colourings: natural and artificial. Natural food colourings include caramelized sugar for brown; annatto, turmeric, and saffron for various shades of orange or yellow; betanin from beets for purple; and even carmine, a deep red dye that is extracted from the cochineal, a small insect that is a parasite on cacti in Central and South America. (That\u2019s right: you may be eating bug juice!)\r\n\r\nSome colourings are artificial. In the United States, the Food and Drug Administration currently approves only seven compounds as artificial colourings in food, beverages, and cosmetics:\r\n
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            1. FD&C Blue #1: Brilliant Blue FCF<\/li>\r\n \t
            2. FD&C Blue #2: Indigotine<\/li>\r\n \t
            3. FD&C Green #3: Fast Green FCF<\/li>\r\n \t
            4. RD&C Red #3: Erythrosine<\/li>\r\n \t
            5. FD&C Red #40: Allura Red AC<\/li>\r\n \t
            6. FD&C Yellow #5: Tartrazine<\/li>\r\n \t
            7. FD&C Yellow #6: Sunset Yellow FCF<\/li>\r\n<\/ol>\r\nLower-numbered colours are no longer on the market or have been removed for various reasons. Typically, these artificial colourings are large molecules that absorb certain colours of light very strongly, making them useful even at very low concentrations in foods and cosmetics. Even at such low amounts, some critics claim that a small portion of the population (especially children) is sensitive to artificial colourings and urge that their use be curtailed or halted. However, formal studies of artificial colourings and their effects on behaviour have been inconclusive or contradictory. Despite this, most people continue to enjoy processed foods with artificial colouring (like those shown in the accompanying figure).\r\n\r\n[caption id=\"attachment_386\" align=\"aligncenter\" width=\"600\"]\"Bottles<\/a> Figure 8.15a \"Food Colouring.\" Artificial food colourings are found in a variety of food products, such as processed foods, candies, and egg dyes. Even pet foods have artificial food colouring in them, although it\u2019s likely that the animal doesn\u2019t care![\/caption]\r\n\r\n<\/div>\r\n
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              Key Takeaways<\/p>\r\n\r\n<\/header>\r\n

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