Metals

Submitted by ChemPRIME Staff on Thu, 01/13/2011 - 14:04



Approximately three-quarters of the known elements display the macroscopic properties characteristic of metals. They conduct both heatEnergy transferred as a result of a temperature difference; a form of energy stored in the movement of atomic-sized particles. and electricity very well; they have shiny surfaces; they are capable of being shaped by hammering (malleableAble to be pounded into various shapes.) and also of being drawn into wires (ductileAble to be drawn into a wire; usually applied to metals, of which ductility is a characteristic property.). These properties can be understood in terms of metallic bonding in which valence electrons are delocalized over an entire metallic crystalA solid with a regular polyhedral shape; for example, in sodium chloride (table salt) the crystal faces are all at 90° angles. A solid in which the atoms, molecules, or ions are arranged in a regular, repeating lattice structure.. Positive metal ions formed by loss of valence electrons are held together by an electron sea. The strength of metallic bonding varies roughly as the number of electrons available in this sea. Chemical properties of the metals include a tendency to lose electrons and form positive ions, and the ability of their oxides to function as bases. The extent of these characteristics varies from one metal to another. Several borderline cases such as B, Si, Ge, As, Sb, and Te are difficult to classify as metals or nonmetals. These elements are usually referred to as the metalloids or semimetals. As you will recall from the discussion of metals on the periodic table, one can draw a zigzag line across the periodic table from B to At which separates the metals from the nonmetals and semimetals. This line is clearly indicated in most periodic tables. Periodic Table Live allows you to select metals, semi-metals, or non-metals and see how they are divided on the periodic table.

A great many metals and alloys are of commercial importance, but metals occur naturally in oxide, carbonate, or sulfide ores. Such ores must be concentratedIncreased the concentration of a mixture or solution (verb). Having a large concentration (adjective). (beneficiated) before they can be reduced to the metal, and usually the raw metal must be purified (refined) in a third step. An excellent example of these processes involves iron which can be readily beneficiated because its ore is ferromagneticDescribes a substance in which magenetism persists after removal of an external magnetic field; able to be a permanent magnet. A ferromagnetic material contains groups of atoms within which the magnetic moments of particles are aligned; in a magnetic field the domains align and they remain aligned after the field is removed.. Iron ore is then reduced in a blast furnace and purified in a steelmaking furnace. Since ore-reduction is a nonspontaneous process, its reverse, oxidationThat part of a chemical reaction in which a reactant loses electrons; simultaneous reduction of a reactant must occur. or corrosion of a metal, is often a problem. This is especially true in the case of iron because the oxide coating which forms on the metal surface does not protect the remaining metal from atmospheric oxidation.

Here we will be concerned mainly with the transition metals. We have already covered metals which are representative elements, such as alkali metals and alkaline earth metals. A discussion of the lanthanoidAn element in the periodic table from lanthanum (atomic number 57) to lutetium (atomic number 71); also called lanthanide. Sometimes lanthanum itself is not included in this series; sometimes lutetium is not. and actinoidAn element in the periodic table from actinium (atomic number 89) to lawrencium (atomic number 103); also called actinide. Sometimes actinium itself is not included in this series; sometimes lawrencium is not. metals is beyond the scope of general chemistry. Since transition metals contain d electrons in their valence shell, their chemistry is somewhat different from that of the representative elements. In particular they form a familyThose elements that comprise a single column of the periodic table. Also called group. of compounds called complexA central metal and the ligands surrounding it; also called coordination complex. compounds or coordination compounds which are very different from those we have encountered up to this point. In these complexes, several ligands which can serve as Lewis bases are bonded to a metal ion which serves as a Lewis acidA species that accepts a pair of electrons to form a covalent bond.. The number of ligands is called the coordination numberThe number of atoms to which a particular atom is bonded; in a coordination complex, the number of positions where ligands are attached to the central metal; in a ionic compound, the number of ions of opposite charge surrounding an ion., and defines the possible geometries of a complex. For a coordination number of 2 the complex is usually linear. Both square planar and tetrahedral structures occur for coordination number 4, and coordination, number 6 usually involves an octahedral structure. Square planar and octahedral structures give rise to cisDescribes the relationship between two atoms or groups of atoms, each attached to one of two doubly bonded carbon atoms and located on the same side of the double bond. Also refers to groups located adjacent to each other in an octahedral or square planar coordination complex.-trans isomerism.

Some ligands, called chelating agents, can coordinate-covalent bondThe attractive force between one atom (nucleus and core electrons) and another atom as a result of sharing electrons. to metal ions at more than one site. ChelateIn coordination chemistry, a ligand that can attach to a central metal through two or more coordinate covalent bonds; a complex consisting of at least one such ligand together with a central metal. complexes are often important in biological systems because they can disguise the charge of a metal ion, stabilizing the ion in a hydrophobicWater-hating; not attracted to water molecules or polar molecules. environment.

In aqueousDescribing a solution in which the solvent is water. solutionA mixture of one or more substances dissolved in a solvent to give a homogeneous mixture. transition-metal ions are usually octahedrally coordinated by water molecules, but often other ligands which are stronger Lewis bases replace water. Such reactions often produce color changes, and they are usually rapid. A few metal ions, such as Cr(III), Co(III), Pt(IV), and Pt(II), undergo ligand substitution rather slowly and are said to be inertUnreactive. Used to describe coordination complexes that exchange ligands slowly or an electrode in an electrochemical cell that serves only as a surface where reaction can occur and is neither consumed nor added to during reaction.. Metal ions whose reactions are rapid are said to be labileReactive; often used to describe coordination complexes that exchange ligands rapidly..