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Learning Objectives

describe how aspects are organized right into the routine table. Define how some attributes of elements relate to your positions top top the routine table.

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In the 19th century, countless previously unknown aspects were discovered, and also scientists detailed that particular sets of aspects had comparable bsci-ch.orgical properties. For example, chlorine, bromine, and also iodine react with other facets (such as sodium) come make similar compounds. Likewise, lithium, sodium, and also potassium react with other elements (such as oxygen) come make comparable compounds. Why is this so?

In 1864, Julius Lothar Meyer, a German bsci-ch.orgist, arranged the aspects by atomic mass and also grouped them according to their bsci-ch.orgical properties. Later that decade, Dmitri Mendeleev, a Russian bsci-ch.orgist, organized all the known facets according to similar properties. The left gaps in his table because that what he thought were undiscovered elements, and also he made part bold predictions regarding the nature of those undiscovered elements. When elements were later found whose properties carefully matched Mendeleev’s predictions, his version of the table gained favor in the clinical community. Because certain properties of the elements repeat ~ above a consistent basis throughout the table (that is, they are periodic), it came to be known together the periodic table.

Mendeleev had to perform some facets out the the order of your atomic masses to group them with other elements that had similar properties.

The periodic table is one of the cornerstones of bsci-ch.orgistry due to the fact that it organizes all of the known elements on the basis of their bsci-ch.orgical properties. A modern version is presented in number \(\PageIndex1\). Most periodic tables provide additional data (such together atomic mass) in a crate that consists of each element’s symbol. The facets are listed in stimulate of atomic number.

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Figure \(\PageIndex1\): A modern Periodic Table. A modern periodic table lists aspects left to right by atom number. An interactivePeriodic table can befound here. (Public Domain; Pubbsci-ch.org via NIH)

Features that the regular Table

Elements the have comparable bsci-ch.orgical properties are grouped in columns referred to as groups (or families). As well as being numbered, several of these teams have names—for example, alkali metals (the an initial column that elements), alkaline earth metals (the second column that elements), halogens (the next-to-last shaft of elements), and noble gases (the last obelisk of elements).

The native halogen originates from the Greek because that “salt maker” because these aspects combine through other elements to kind a team of compounds referred to as salts.


To your Health: Radon

Radon is one invisible, odorless noble gas the is gradually released indigenous the ground, specifically from rocks and soils who uranium contents is high. Since it is a noble gas, radon is no bsci-ch.orgically reactive. Unfortunately, the is radioactive, and also increased exposure come it has actually been correlated with an increased lung cancer risk.

Because radon comes from the ground, we cannot stop it entirely. Moreover, since it is denser than air, radon often tends to accumulate in basements, which if improperly ventilated deserve to be hazardous to a building’s inhabitants. Fortunately, devoted ventilation minimizes the quantity of radon that can collect. Special fan-and-vent solution are accessible that attract air from listed below the basement floor, before it can enter the life space, and vent it over the roof of a house.

After smoking, radon is believed to be the second-biggest preventable cause of lung cancer in the united States. The American Cancer society estimates that 10% of every lung cancers are regarded radon exposure. There is uncertainty regarding what levels of exposure cause cancer, and what the specific causal agent can be (either radon or among its malfunction products, numerous of i m sorry are likewise radioactive and, unlike radon, no gases). The US ecological Protection agency recommends experimentation every floor below the third floor for radon level to guard against long-term health effects.


Each heat of facets on the periodic table is dubbed a period. Durations have various lengths; the first period has actually only 2 facets (hydrogen and helium), while the 2nd and third periods have 8 elements each. The fourth and fifth periods have actually 18 aspects each, and later periods are so lengthy that a segment from every is removed and placed beneath the main body that the table.

Certain elemental properties become apparent in a inspection of the regular table as a whole. Every element can it is in classified together either a metal, a nonmetal, or a metalloid (or semi metal), as shown in figure \(\PageIndex2\). A metal is a substance the is shiny, frequently (but not always) silvery in color, and an excellent conductor the electricity and heat. Metals are also malleable (they have the right to be beaten right into thin sheets) and ductile (they can be attracted into slim wires). A nonmetal is typically dull and also a negative conductor the electricity and also heat. Heavy nonmetals space also really brittle. As presented in figure \(\PageIndex2\), metals occupy the left three-fourths the the regular table, if nonmetals (except for hydrogen) are clustered in the upper right-hand edge of the routine table. The elements with properties intermediate between those of metals and nonmetals are referred to as metalloids (or semi-metals). Elements surrounding to the bold line in the right-hand section of the periodic table have semimetal properties.

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api/deki/files/28863/2.9.jpg?revision=1&size=bestfit&width=609&height=346" />Figure \(\PageIndex3\): one-of-a-kind Names because that Sections the the periodic Table. (CC BY-NC-SA; anonymous by request)




Group 17: The Halogens

The halogens space fluorine, chlorine, bromine, iodine, and also astatine. The surname halogen is acquired from the Greek words for “salt forming,” which reflects that all of the halogens react easily with steels to type compounds, together as salt chloride and also calcium chloride (used in some areas as road salt).

Compounds the contain the fluoride ion are included to toothpaste and the water it is provided to stop dental cavities. Fluorine is likewise found in Teflon coatings on kitchen utensils. Although chlorofluorocarbon propellants and refrigerants are thought to cause the depletion of Earth’s ozone layer and contain both fluorine and also chlorine, the last is responsible because that the adverse impact on the ozone layer. Bromine and also iodine are less abundant than chlorine, and also astatine is for this reason radioactive that it exists in just negligible amounts in nature.

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Group 18: The Noble Gases

The noble gases space helium, neon, argon, krypton, xenon, and radon. Since the noble gases are composed that only single atoms, they are referred to as monatomic. In ~ room temperature and pressure, they space unreactive gases. Because of their absence of reactivity, for plenty of years lock were dubbed inert gases or rarely gases. However, the very first bsci-ch.orgical compounds containing the noble gases were all set in 1962. Return the noble gases are reasonably minor constituents of the atmosphere, herbal gas includes substantial amounts of helium. Since of its short reactivity, argon is often used together an unreactive (inert) atmosphere for welding and in light bulbs. The red light emitted by neon in a gas discharge tube is used in neon lights.