Читать книгу Geology and Mineralogy of Gemstones - Karl Wallace, David Turner R. - Страница 20

A group is a column of elements in the periodic table (Figure 1.3). Elements within a group have similar chemical behavior because of the similarity in the distribution of their electrons, especially in the valence (outermost) shell. The elements of the first group are called the alkali metals and tend to give up an electron, resulting in a characteristic +1 valence charge. A familiar element in this group is sodium (Na), part of the NaCl (table salt) molecule. Although hydrogen sits at the top of the column, it does not actually belong to the alkali metals group.

The elements of the second group are collectively called the alkaline earth metals. These elements usually lose two electrons, resulting in a characteristic +2 valence charge. Calcium (Ca) and magnesium (Mg), two of the important bone‐forming ingredients, are elements of this group.

The middle block of elements (ranging from Sc down and across to element 112, Cn) are called the transition metals. These elements can have variable valence charges, usually up to +4 but sometimes as high as +6. Note how the precious metals Cu (copper), Ag (silver), and Au (gold) are all Group 1B transition metals and thus share similar physical properties. The metals Ni (nickel), Pd (palladium), and Pt (platinum) are similarly related as Group VII elements. The transition elements often endow gemstones with their striking colors.

Elements classified as semi‐metals or other metals include aluminum (Al) and lead (Pb). The next group are the metalloids, including silicon (Si) and arsenic (As). Nonmetals include the biologically important elements carbon (C), nitrogen (N), oxygen (O), phosphorus (P), and sulfur (S).

The halogens occupy the seventeenth column and will almost always have a –1 charge. Familiar elements in this group are chlorine (Cl) and iodine (I). Elements on the far right are the noble gases, which do not combine with other elements. Notable gases in this group are helium (He) and neon (Ne). The two large blocks below the table are the Lanthanide and Actinide series elements.

Figure 1.3 Periodic table of the elements with atomic numbers and chemical abbreviations. Dashed and dotted borders indicate the element is not naturally occurring.