Earth Materials. John O'Brien. Читать онлайн. Newlib. NEWLIB.NET

Автор: John O'Brien
Издательство: John Wiley & Sons Limited
Серия:
Жанр произведения: География
Год издания: 0
isbn: 9781119512219
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      2.2.4 Atomic and ionic radii

Schematic illustration of radii (in angstroms) of some common cations in relationship to the atomic radius of the neutral atoms.

      Electrons in the outer, higher energy electron levels are least tightly bound to the positively charged nucleus. This weak attraction results because these electrons are farthest from the nucleus and because they are shielded from the nucleus by the intervening electrons that occupy lower quantum level positions closer to the nucleus. These outer electrons or valence electrons are the electrons that are involved in a wide variety of chemical reactions, including those that produce minerals, rocks, and a wide variety of synthetic materials. The loss or gain of these valence electrons produces anions and cations, respectively.

Schematic illustration of radii (in angstroms) of some common anions in relationship to the atomic radius of the neutral atoms. Schematic illustration of radii (in angstrom units) of some common anions and cations of sulfur in relationship to the neutral atom radius.

      2.3.1 The basics

      Atoms in minerals, rocks, and other Earth materials are held together by forces or mechanisms called chemical bonds. The nature of these bonds strongly influences the properties and behavior of these materials. The nature of the bonds is, in turn, strongly influenced by the electron configuration of the elements that combine to produce the mineral, rock or other material.

      Five principle bond types and many hybrids occur in minerals. The three most common bond types are (1) ionic, (2) covalent, and (3) metallic. They can be modeled based on the behavior of valence electrons in the outer quantum levels of atoms. During bonding, valence electrons display varying tendencies to change position based on their periodic properties. In discussing chemical bonds, it is useful to divide elements into those that are metallic and those that are nonmetallic.

      Ionic bonds involve the linking together of metallic and nonmetallic elements, covalent bonds involve the linking of two nonmetallic elements, and metallic bonds involve the linking of two metallic elements. Hybrids between these bond types are common. Minerals with such hybrid or transitional bonds commonly possess combinations of features characteristic of each bond type. Other bond types include van der Waals and hydrogen bonds. Chemical bonding is a very complicated process; the models used below are simplifications designed to make this complex process easier to understand to a reasonable degree.