The first element appearing on the list that is not a main group element is iron, at 0.006 percentage by mass. To Your Health: Transition Metals in the BodyĪccording to Table 2.2 “Elemental Composition of a Human Body”, most of the elemental composition of the human body consists of main group elements. Elements adjacent to the bold line in the right-hand portion of the periodic table have semimetal properties, with the exception of aluminum, which is a metal. The elements with properties intermediate between those of metals and nonmetals are called semimetals (or metalloids). As shown in Figure 2.8 “Types of Elements”, metals occupy the left three-fourths of the periodic table, while nonmetals (except for hydrogen) are clustered in the upper right-hand corner of the periodic table. A nonmetal is typically dull and a poor conductor of electricity and heat. Metals are also malleable (they can be beaten into thin sheets) and ductile (they can be drawn into thin wires). A metalis a substance that is shiny, typically (but not always) silvery in color, and an excellent conductor of electricity and heat. Every element can be classified as either a metal, a nonmetal, or a semimetal, as shown in Figure 2.8 “Types of Elements”. The fourth and fifth periods have 18 elements each, and later periods are so long that a segment from each is removed and placed beneath the main body of the table.Ĭertain elemental properties become apparent in a survey of the periodic table as a whole. Periods have different lengths the first period has only 2 elements (hydrogen and helium), while the second and third periods have 8 elements each. The US Environmental Protection Agency recommends testing every floor below the third floor for radon levels to guard against long-term health effects.Įach row of elements on the periodic table is called a period. It is uncertain what levels of exposure cause cancer, and what the exact causal agent might be, radon gas or one of its solid breakdown products. The American Cancer Society estimates that 10% of all lung cancers are related to radon exposure. Special fan-and-vent systems are available that draw air from below the basement floor, before it can enter the living space, and vent it above the roof of a house.Īfter smoking, radon is thought to be the second-biggest preventable cause of lung cancer in the United States. Fortunately, specialized ventilation minimizes the amount of radon that might collect. Moreover, because it is denser than air, radon tends to accumulate in basements, which if improperly ventilated can be hazardous to a building’s inhabitants. Unfortunately, it is radioactive, changing into other radioactive elements through series of nuclear decay events.īecause radon comes from the ground, we cannot avoid it entirely. Because it is a noble gas, radon is not chemically reactive. Radon is an invisible, odorless noble gas that is slowly released from the ground, particularly from rocks and soils whose uranium content is high. Because certain properties of the elements repeat on a regular basis throughout the table (that is, they are periodic), it became known as the periodic table. When elements were later discovered whose properties closely matched Mendeleev’s predictions, his version of the table gained favor in the scientific community. He left gaps in his table for what he thought were undiscovered elements, and he made some bold predictions regarding the properties of those undiscovered elements. Later that decade, Dmitri Mendeleev, a Russian chemist, organized all the known elements according to similar properties. In 1864, Julius Lothar Meyer, a German chemist, organized the elements by atomic mass and grouped them according to their chemical properties.
Likewise, lithium, sodium, and potassium react with other elements (such as oxygen) to make similar compounds. For example, chlorine, bromine, and iodine react with other elements (such as sodium) to make similar compounds. In the 19th century, many previously unknown elements were discovered, and scientists noted that certain sets of elements had similar chemical properties.