For example: Fluorine and oxygen are the strongest oxidizing elements known. The changes in state as one moves down the halogen family offer excellent examples of the increasing strength of intermolecular London forces with increasing molecular mass and increasing polarizability. Within any period, the strongest oxidizing agent is in group 17. One of the primary characteristics of nonmetals is that they form chemical compounds by making covalent and ionic bonds. The halogens form diatomic molecules in which each atom is involved in only one bond. In normal chemical processes, nonmetals do not form monatomic positive ions (cations) because their ionization energies are too high. If necessary, the elements form enough covalent bonds to supplement the electrons already present to possess an octet. Red phosphorus (shown in (Figure 3.5.6)) is denser, has a higher melting point (~600 °C), is much less reactive, is essentially nontoxic, and is easier and safer to handle than is white phosphorus. (2) Nitrogen in the atmosphere exists as very stable diatomic molecules. This method works because there are only weak London dispersion forces between the layers in graphite. Alternative methods are to deposit a single layer of carbon atoms on the surface of some other material (ruthenium, iridium, or copper) or to synthesize it at the surface of silicon carbide via the sublimation of silicon. The reasons for this include smaller size, greater ionization energy, and (most important) the fact that the first member of each group has only four valence orbitals (one 2s and three 2p) available for bonding, whereas other group members have empty d orbitals in their valence shells, making possible five, six, or even more bonds around the central atom. Under normal conditions, more than half of the nonmetals are gases, one is a liquid, and the rest include some of the softest and hardest of solids. All Rights Reserved. Cooling this liquid gives long needles of monoclinic sulfur. Graphite, also shown in (Figure 3.5.2), is a soft, slippery, grayish-black solid that conducts electricity. Nonmetal structures contain covalent bonds, and many nonmetals consist of individual molecules. When did organ music become associated with baseball? Both of the forms bear some relationship to graphite. Its structure is highly polymeric and appears to contain three-dimensional networks of P4 tetrahedra joined by P-P single bonds. Form Covalent/Ionic Bonds. For example, members of group 15 have five valence electrons and require only three additional electrons to fill their valence shells. Carbon nanotubes are carbon allotropes, which have a cylindrical structure. As a solid, as a liquid, as a gas, and in solution, white phosphorus exists as P4 molecules with four phosphorus atoms at the corners of a regular tetrahedron, as illustrated in (Figure 3.5.6). The dangling atoms at the ends of the chains of sulfur atoms are responsible for the dark red color because their electronic structure differs from those of sulfur atoms that have bonds to two adjacent sulfur atoms. This is buckminsterfullerene (often called bucky balls) after the architect Buckminster Fuller, who designed domed structures, which have a similar appearance (Figure 3.5.4). The strength of carbon nanotubes will eventually lead to some of their most exciting applications, as a thread produced from several nanotubes will support enormous weight. There are currently nanotubes in some bicycle parts, skis, baseball bats, fishing rods, and surfboards. How will understanding of attitudes and predisposition enhance teaching? As the temperature rises, S-S bonds in the rings break, and polymeric chains of sulfur atoms result. There are five general aspects of the oxidation-reduction chemistry: With the exception of most of the noble gases, all nonmetals form compounds with oxygen, yielding covalent oxides. Cooling the liquid rapidly produces a rubberlike amorphous mass, called plastic sulfur. How long does it take to cook a 23 pound turkey in an oven? Graphene is a single layer of graphite (one atom thick), as illustrated in (Figure 3.5.5), whereas carbon nanotubes roll the layer into a small tube, as illustrated in (Figure 3.5.5). For example, nitrogen forms only NF, Vishakha Monga, Paul Flowers, Klaus Theopold, William R. Robinson, and Richard Langley, Inorganic Chemistry for Chemical Engineers, Next: 3.6 Occurrence, Preparation, and Compounds of Hydrogen, Creative Commons Attribution 4.0 International License, Describe structure and properties of nonmetals. Most nonmetals have the ability to gain electrons easily. The noble gases are all monatomic, whereas the other nonmetal gases—hydrogen, nitrogen, oxygen, fluorine, and chlorine—normally exist as the diatomic molecules H2, N2, O2, F2, and Cl2. low melting point,low density,not a conductor. Unlike graphite and graphene, which occur in layers, the layers wrap into a tube and bond together to produce a stable structure. The addition of nanotubes to polymers improves the mechanical, thermal, and electrical properties of the bulk material. Each atom forms four single bonds to four other atoms at the corners of a tetrahedron (sp3 hybridization); this makes the diamond a giant molecule. Depending upon the shape of the nanotube, it may be a conductor or semiconductor. The elements of group 16 require only two additional electrons. At room temperature, it gradually reverts to the rhombic form. Another difference between the first group member and subsequent members is the greater ability of the first member to form π bonds. The nonmetals exhibit a rich variety of chemical behaviors. By the end of this section, you will be able to: The nonmetals are elements located in the upper right portion of the periodic table. The weak forces between layers give graphite the soft, flaky character that makes it useful as the so-called “lead” in pencils and the slippery character that makes it useful as a lubricant. To learn more, see the discussion in the chapter on acid-base chemistry. This form is stable from 96 °C to the melting point, 119 °C. The walls of the tube may be one atom or multiple atoms thick. Andre Geim and Kostya Novoselov at the University of Manchester won the 2010 Nobel Prize in Physics for their pioneering work characterizing graphene. How long will the footprints on the moon last? Carbon-carbon single bonds are very strong, and, because they extend throughout the crystal to form a three-dimensional network, the crystals are very hard and have high melting points (~4400 °C). Periodic Table: Elements are arranged on the Periodic Table according to their properties. The binary hydrogen compounds of the nonmetals also exhibit an acidic behavior in water, although only HCl, HBr, and HI are strong acids. Each sulfur atom is bonded to each of its two neighbors in the ring by covalent S-S single bonds.
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