Introduction
This section provides an outline of how this book is organized, following how the elements are listed in the periodic table of the chemical elements. Elements are not only arranged according to the number of protons in their nuclei, but are also classified as metals or nonmetals, with a group of transition elements between the two categories. The major section of this book is the guide that is organized as follows.
The guide starts with the alkali metals and continues with the alkali earth metals, followed by the three series of transition elements. These series are followed by the metallics, which leads to the metalloids of group 14 and then to the metalloids of group 15. This is the end of the common elements that are considered “metals” and the beginning of the nonmetals, halogens, and noble gases. The nonmetals are then followed by groups of less common metals know as the lanthanide series, the actinide series (including the transuranic series), and finally the transactinide series, which includes the newer artificially man-made radioactive superac- tinides (or super heavy elements) and possible future elements.
Most of the elements listed on the periodic table are considered metals or metal-like, which is related to the oxidation states of metals. Metallic elements have oxidation states that form positive ions (cations) when they combine with nonmetals by giving up or sharing one or more electrons. Most metals have less than four electrons in their outer valence shell. Some of the heavier metals are unique in that they can also add electrons to the shells inside the outer shell. Since they “give up” or share electrons in chemical reactions, they are classified as having low or weak electronegativity, and thus they become positive ions. If they are in an electrolytic solution, they are called cations because they collect at the negative pole or cathode. Cations have more protons in their nuclei than electrons in their shells. In addition, their remaining electrons are more strongly attracted to their positive nuclei; thus, metallic ions are generally smaller than atoms of the same elements. This ionization process can be depicted for the metallic elements lithium as Li → Li+ + e-, and for calcium as Ca → Ca++ + 2e-.
Anions are just the opposite. They are atoms that have gained electrons and thus are ions with a negative charge; they are “electronegative” because they have a tendency to be nega-
tively charged. Anions collect at the positive anode in an electrolytic solution. The electron attractions between nuclei are weaker for anions; thus, in general, negative ions are larger than are the atoms of the same elements from which they were formed. When nonmetal atoms gain electrons, they become anions. For example, oxygen gains two electrons in most chemi- cal reactions: O + 2e-→ O2-. The halogens and sulfur, in addition to oxygen, are also highly
electronegative.
The metals are grouped on the left side of the periodic table and, to some extent, to the center. As you move from the far left side of the table to the right side, the very reactive metals (alkali metals and alkali-earth metals) are followed by less active metals, or transition metals, and the table then moves to metalloids and semiconducting elements before proceeding to nonmetals, whose outer valence shells tend to gain electrons when reacting with metals. As the number of electrons in the outer shells increases, the distance between the nucleus and electrons also increases. The further the electrons are from the nucleus, the weaker the attrac- tion between the electrons and the positive nucleus. Thus, in general, the ionization energy increases from left to right in the periodic table. Therefore, the larger the molecules of metallic elements, the greater their volume, as is true with all three-dimensional objects. In addition, their densities become greater as do their atomic weights, and in general, the higher their atomic mass, the lower will be their melting and boiling points.
Ionization is the process whereby a chemical reaction forms ions (atoms with a negative or positive charge) from the breakup of neutral molecules of some inorganic compounds. A common example is the neutral molecule of sodium chloride (NaCl, salt). When it dissoci- ates (breaks apart) into positive metallic ions of Na+ by the loss of an electron, the nonmetal
chlorine ion Cl- gains the negative charge given up by the sodium atom.
Approximately 75% of all elements found on and in the Earth are metals. They are crystal- line solids that at room temperature range from hard to butter-like soft to liquid (mercury). They are generally good conductors of heat and electricity as a result of the swarm of relatively “free” electrons in their outer shell that move without much resistance to other elements, particularly those with a dearth of electrons in their outer shells. In pure states, most metals have a shiny luster when cut. Those located at the far left of the table have only one electron in their outer shell. Therefore, they are very reactive and are not usually found in pure form. Instead, they are found in compounds, minerals, or ores that must be processed to extract the pure metal from the other elements in the compounds.
Metals may be classified by a variety of categories. Some metals fit more than one of the following categories:
1. Alkali metals—Group 1 (IA), soft, silvery, and very active (electropositive). They are all solids and have one electron in their outer valence shell. The alkali metals begin each period, 2 to 7, on the periodic table. They are very reactive and, in the pure metallic state, must be stored in oil and not exposed to air or water. Even though hydrogen may be considered a nonmetal, it is included in group 1 with the alkali metals because it has a single proton in its nucleus and just one electron in its valence shell and, thus, usually acts like a metal. Under certain situations, hydrogen can also act as a nonmetal. 2. Alkali earth metals—Group 2 (IIA), shades of white to subtle colors, malleable, machin-
able, and less active than alkali metals. They are all solids and have two electrons in their outer valence shell.
Guide to the Elements | 37 3. Transition metals—found in the groups located in the center of the periodic table, plus
the lanthanide and actinide series. They are all solids, except mercury, and are the only elements whose shells other than their outer shells give up or share electrons in chemical reactions. Transition metals include the 38 elements from groups 3 through 12. They exhibit several oxidation states (oxidation numbers)and various levels of electronegativ- ity, depending on their size and valence.
4. Other metals—a classification given to seven metals that do not fit the characteristics of transition metals. They do not exhibit variable oxidation states, and their valence electrons are found only on the outer shell. They are aluminum, gallium, indium, tin, thallium, lead, and bismuth.
5. Metalloids—metals found in the region of the periodic table between groups of metals and nonmetals. Thus, they have some characteristics of both metals and nonmetals. Some are semiconductors. They are boron, silicon, germanium, arsenic, antimony, tellurium, and polonium.
6. Noble metals—refers to several unreactive metals that do not easily dissolve in acids or
oxidize in air (e.g., platinum, gold, and mercury). They include the platinum group of metals (see next item). They are called “noble” because of their resistance to reacting with other elements.
7. Platinum metals—includes unreactive transition elements located in groups 8, 9, and 10 of periods 5 and 6. They have similar chemical properties. They are ruthenium, rhodium, palladium, osmium, iridium, and platinum.
8. Rare-earth metals—a loose term for less well-known metallic elements. They include the so-called rare-earths. The rare-earths are not actually rare (scarce); historically, some of them were just difficult to find, isolate, and identify.
9. Lanthanide metals—also rare-earth elements with atomic numbers ranging from 57 through 71.
10. Actinide metals—includes elements with atomic numbers from 89 to 111. Also includes the transuranic elements (e.g., beyond uranium [92U to 103Lr]) and the superactinides (elements with atomic numbers 104 to 118 that are artificial, radioactive, and unstable with very short half-lives).
11. Light metals—a general term for elements relatively light in weight but strong enough for construction. Some examples are aluminum, magnesium, titanium, and beryllium. 12. Heavy metals—a general term for metals with an atomic mass number greater than 200.
Several heavy metals are extremely toxic.
Metals are extremely important not only for chemical reactions but also for the health and welfare of plants and animals. Some examples of metals required for good nutrition, even in trace amounts, are iron, copper, cobalt, potassium, sodium, and zinc. Other metals—for example, mercury, lead, cadmium, barium, beryllium, radium, and uranium—are very toxic. Some metals at the atomic and ionic levels are crucial for the oxidation process that metabo- lizes carbohydrates for all living cells.