![]() We need phosphorus for our bones and teeth, and it is a crucial component of all living cells. Phosphorus makes up 1.1% of the human body but only 0.105% of Earth’s crust. ![]() There is an element that we need more of in our bodies than is proportionately present in Earth’s crust, and this element is not easily accessible. Looking Closer: The Phosphorous Bottleneck On the other hand, although carbon is present in the atmosphere as carbon dioxide, and about 80% of the atmosphere is nitrogen, we obtain those two elements from the food we eat, not the air we breathe. We obtain oxygen from the air we breathe and the water we drink. How does the human body concentrate so many apparently rare elements? The relative amounts of elements in the body have less to do with their abundances on Earth than with their availability in a form we can assimilate. Oxygen has the highest percentage in both cases, but carbon, the element with the second highest percentage in the body, is relatively rare on Earth and does not even appear as a separate entry carbon is part of the 0.174% representing “other” elements. If you compare both compositions, you will find disparities between the percentage of each element in the human body and on Earth. Classify each element in Conceptual Problem 1 ( Section 1.\) also lists the relative abundances of elements in the human body.Other important groupings of elements in the periodic table are the main group elements, the transition metals, the lanthanides, and the actinides. 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. 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. As you might expect, elements colored in gold 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 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 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. \) The Periodic Table Showing the Elements in Order of Increasing Z
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