(The inner electrons are called core electrons.) The valence electrons largely control the chemistry of an atom. The electrons in the highest-numbered shell, plus any electrons in the last unfilled subshell, are called valence electrons the highest-numbered shell is called the valence shell. The periodic table is separated into blocks depending on which subshell is being filled for the atoms that belong in that section. Despite this, most people continue to enjoy processed foods with artificial coloring (like those shown in the accompanying figure).\): Blocks on the Periodic Table. However, formal studies of artificial colorings and their effects on behaviour have been inconclusive or contradictory. Even at such low amounts, some critics claim that a small portion of the population (especially children) is sensitive to artificial colorings and urge that their use be curtailed or halted. Typically, these artificial colorings are large molecules that absorb certain colors of light very strongly, making them useful even at very low concentrations in foods and cosmetics. Lower-numbered colors are no longer on the market or have been removed for various reasons. In the United States, the Food and Drug Administration currently approves only seven compounds as artificial colorings in food, beverages, and cosmetics: (That’s right: you may be eating bug juice!) Natural food colorings 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. There are two types of food colorings: natural and artificial. Many processed foods have food colorings added to them. Many foods, such as tomatoes, are highly colored in fact, the common statement “you eat with your eyes first” is an implicit recognition that the visual appeal of food is just as important as its taste. A red tomato, for example, is bright red because it reflects red light while absorbing all the other colors of the rainbow. Although colored lights produce their colors, objects are colored because they preferentially reflect a certain color from the white light that shines on them. The color of objects comes from a different mechanism than the colors of neon and other discharge lights. Indeed, the electron configuration of Se is 4 s 23 d 104 p 4, as expected. This means that its electron configuration should end in a p 4 electron configuration. It is in the fourth column of the p block. Consider Se, as shown in Figure 10 “Selenium on the Periodic Table”. Similarity of valence shell electron configuration implies that we can determine the electron configuration of an atom solely by its position on the periodic table. However, many similarities do exist in these blocks, so a similarity in chemical properties is expected. In the d and f blocks, because there are exceptions to the order of filling of subshells with electrons, similar valence shells are not absolute in these blocks. This is strictly true for all elements in the s and p blocks. Elements in each column have the same valence shell electron configurations, and the elements have some similar chemical properties. The same concept applies to the other columns of the periodic table. 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. Because much of the chemistry of an element is influenced by valence electrons, we would expect that these elements would have similar chemistry- and they do. They all have a similar electron configuration in their valence shells: a single s electron.
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