Structural Biochemistry/Metallic Behavior

Definition

Metals are typically located within the left and lower areas of the periodic table, and they can be defined as solids that have relatively high melting points. In addition, another characteristic of metals is that they are typically shiny and act as good thermal and electrical conductors. Nonmetals, on the other hand are located within the upper right side of the periodic table. Metalloids can be observed in the region between these two classes and hold properties that exemplify traits of both metals and nonmetals.

Metal behavior is described as chemical properties of elements that are metals. These traits are all based on one fact. That fact is the relative ease of metals to lose electrons or to be oxidized. The trends can be explained through chemistry. Across a period, metallic character decreases because atoms more readily accept electrons to fill a valence shell. Down a group, metallic character increases because as the atomic radius becomes larger, the electrons are more easily lost or reduced!

Chemical Properties of Metals: Metals combine with other metals and some non-metallic elements to form a vast number of alloys that enhance the properties of metals in specific applications. For example, the combination of iron, nickel and chromium provides a series of stainless steel alloys that are in common use. Metals such as nickel, vanadium, molybdenum, cobalt, rare earths and the platinum group metals enable the catalytic reactions for the synthesis of many organic chemicals from petroleum. A wide variety of metal compounds and salts impart beneficial properties to products like plastics in terms of colour, brightness, flame resistance and resistance to degradation. Photography has been made possible by the effect of light on metal salts.

Mechanical Properties of Metals: The properties of strength and ductility enable the extensive use of metals in structures and machinery. Metals and alloys exhibit ductility, malleability and the ability to be deformed plastically (that is, without breaking), making them easy to shape into beams (steel beams for construction), extrusions (aluminum frames for doors and windows), coins, metal cans and a variety of fasteners (nails and paper-clips). The strength of metals under pressure (compression), stretching (tensile) and sheer forces makes them ideal for structural purposes in buildings, automobiles, aircraft frames, gas pipelines, bridges, cables, and some sports equipment.

Conductivity of Metals: Metals are excellent conductors of both heat and electricity. In general, conductivity increases with decreasing temperature, so that, at absolute zero (-273°C), conductivity is infinite. To emphasize, metals become superconductors. Thermal conductivity is harnessed in automobile radiators and cooking utensils. Electrical conductivity provides society with the ability to transmit electricity over long distances to provide lights and power in cities remote from electrical generating stations. The circuitry in household appliances, television sets and computers rely on electrical conductivity. Resistance to Wear, Corrosion, Fatigue and Temperature: Metals are hard and durable. They are used in applications sensitive to corrosion such as chemical plants, food preparation, medical applications, plumbing and lead in storage batteries. Wear resistance is critical in bearings for all modes of transportation and in machine tools. Fatigue resistance is the ability to resist breaking after repeated deformation such as bending, which enables the use of metals in springs, levers and gears. Temperature resistance makes metals suitable for jet engines and filaments in light-bulbs. Optical characteristics: Metals are uniformly lustrous and, except for copper and gold, are silvery or greyish. The reason is because all metals absorb light at all frequencies and immediately radiate it. Metals impart mirrors with their reflective surface. The lustre of metals gives them the attractive appearance that is so important in jewellery and coins. Metals provide the intangible, distinctive metallic ring that is associated with coins.

Magnetic Properties: Ferromagnetism is exhibited by iron and several other metals. In addition, other metals and alloys can be magnetized in an electrical field to exhibit paramagnetism. Magnetic properties are employed in electric motors, generators, and speaker systems for audio equipment. Emission Properties: Metals emit electrons when exposed to radiation (for example: light) of a short wavelength or when heated to sufficiently high temperatures. These phenomena are exploited in television screens, using rare earth oxides and in a variety of electronic devices and instruments. Conversely, the ability of metals such as lead to absorb radiation is employed in shielding. For instance, in the apron provided by dentists during an X-ray examination.

Trends

Across the Period

Metallic behavior tends to decrease from the left of the period to the right, due to the increasing number of valence electrons and the decreasing atomic radius.

Across the Group

Metallic behavior tends to increase from top to bottom, due to the increase in the number of electron shells and atomic radius.

Coordination Compounds

The interpretation of spectra of coordination compounds is important in identifying the lowest energy form. First, the energy levels are sketched to show the d electrons. Then the spin multiplicity of the lowest-energy state is equal to the number of unpaired electrons. The maximum possible M1 values for the configuration are determined, which determines the ground term. The selection rules are stated as: 1) The bonds in transition metal complexes vibrate so that they may temporarily change their geometry. This is called vibronic coupling, which provide a vibration that distorts the central atom. This is called the Laporte selection rule. 2) Tetrahedral complexes often absorb more strongly than octahedral compleses of the same metal. The sigma bonding in transition metal complexes can be described as a mixing of p-orbital character. 3) Spin-orbit coupling provides a mechanism for the second selection rule, which states that transitions between states of different spins are not allowed. This is called the spin selection rule.

References

1. Silberberg, Martin S. Principles of General Chemistry. Boston: McGraw-Hill Higher Education, 2007. Print.

Miessler, Gary. Inorganic Chemistry. 4th Edition.