In contrast, nonmetals that form giant structures, such as chains of up to 1,000 selenium atoms, sheets of carbon atoms in graphite, or three-dimensional lattices of silicon atoms have higher melting and boiling points, and are all solids, as it takes more energy to overcome their stronger covalent bonds. Nonmetals existing as discrete atoms like xenon, or as small molecules, such as oxygen, sulfur, and bromine, have low melting and boiling points many are gases at room temperature, as they are held together by weak London dispersion forces acting between their atoms or molecules. This variability in form stems from variability in internal structures and bonding arrangements. The solid elements have low densities and low mechanical and structural strength (being brittle or crumbly), but a wide range of electrical conductivity. The gaseous and liquid nonmetals have very low densities, melting and boiling points, and are poor conductors of heat and electricity. Bromine, the only liquid, is so volatile that it is usually topped by a layer of its fumes sulfur is the only colored solid nonmetal. Ībout half of nonmetallic elements are gases most of the rest are shiny solids. Which elements are included depends on the properties regarded as most representative of nonmetallic or metallic character. There is no widely-agreed precise definition of a nonmetal any list of such is open to debate and revision. When combined with oxygen, nonmetals tend to form acidic oxides (while metals usually form basic oxides). They lack most properties commonly associated with metals: shininess, malleability, ductility, and good thermal and electrical conductivity. Nonmetallic chemical elements generally have low density and high electronegativity. The chemistry of arsenic is predominately nonmetallic. The lemon-yellow vapor smells like garlic. Like carbon, arsenic (here sealed in a container to prevent tarnishing) vaporizes rather than melts when heated. Since then about two dozen properties have been suggested as single criteria for distinguishing nonmetals from metals.ĭefinition and applicable elements Properties discussed in this article are those of the most stable form of elements in ambient conditions unless otherwise stated. While a distinction between metals and other minerals had existed since antiquity, a basic classification of chemical elements as metallic or nonmetallic emerged only in the late 18th century. Most nonmetallic elements were not identified until the 18th and 19th centuries. Hydrogen, oxygen, carbon, and nitrogen are essential building blocks for life. The great variability of nonmetal properties enable specific elements to have unique uses, for example, in electronics, energy storage, agriculture, and chemical production. Five nonmetallic elements-hydrogen, carbon, nitrogen, oxygen, and silicon-make up the overwhelming majority of Earth's oceans, atmosphere, biosphere, and crust. The two lightest nonmetals, hydrogen and helium, together make up about 98% of the mass of the observable universe. Nonmetals are often poor conductors of heat and electricity, and are brittle or crumbly as solids. They range from colorless gases like hydrogen to shiny solids like iodine. Nonmetals tend to have low density and high electronegativity (the ability of an atom in a molecule to attract electrons to itself). This article also covers six borderline elements (the metalloids), some or all of which are sometimes considered nonmetals. Seventeen elements are widely recognized as nonmetals. Status as nonmetal or metal unconfirmed Ī nonmetal is a chemical element that mostly lacks distinctive metallic properties. Nonmetals in their periodic table context For nonmetallic substances, see materials science. For the use of the term nonmetal in astronomy, see nonmetal (astrophysics). This article is about a class of two dozen or so chemical elements.
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