Ions and Their Compounds

An atom or group of atoms that has a positive or negative charge 

We have seen that an atom has a certain number of protons in its nucleus and an equal number of electrons in the space around the nucleus. This results in an exact balance of positive and negative charges. We say that an atom is a neutral entity—it has zero net charge. 

We can produce a charged entity, called an ion, by taking a neutral atom and adding or removing one or more electrons. For example, a sodium atom (Z = 11) has eleven protons in its nucleus and eleven electrons outside its nucleus. 

If one of the electrons is lost, there will be eleven positive charges but only ten negative charges. This gives an ion with a net positive one (1+) charge (11+) + (10-) = 1 +. We can represent this process as follows  

76 Chapter 3 Chemical Foundations Elements, Atoms, and Ions 

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It is interesting to note that the history of medical treatment with metal ions and their compounds has been known for thousands of years. In 2500 b.c., the Chinese used gold (Aurum, Au) for medical treatment, whereas in the middle of this past millennium, the gold s compounds were considered an effective treatment against leprosy. 

Their ions and their compounds are usually colored. 

The recognition that various metal ions and their compounds induce toxic effects has led to recommendations, e.g., by the World Health Organization (WHO), about the acceptable daily intake (ADI) of such metals and their compounds some of these values are listed in Table 2 [25-27]. Closely connected herewith are governmental regulations concerning limiting values of dust components in ambient air some values valid for the Federal Republic of Germany and Switzerland are listed in Table 3 [28,29]. 

The content of this book reflects much contemporary knowledge on the role of metal ions and their compounds in clinical chemistry, especially on the procedures for their analytical determination. However, it can also be recognized that much work has yet to be done e.g., in many instances the so-called normal levels of an element are ill defined or unknown for various metals the knowledge on the physiological properties is incomplete furthermore, the speciation, i.e., the form in which the metals exist in blood, serum, urine, etc., is often only vaguely or not at all understood. 

The chemistry of the rare earths is characterized by the similarity in the properties of the trivalent ions and their compounds. Krumholz (1964) reviewed the structure, properties, solubilities and coordination chemistry of rare earth ions in solution. Moeller (1961) reviewed the electronic configurations, size relationships and various oxidation states of rare earths. Camall (1979) reviewed the literature on the absorption and fluorescence spectra of rare earth ions in solution. The complexes formed by rare earth ions have been reviewed by Thompson (1979). 

Compounds tend to be eovalent. Metals form eomplex ions and their oxides are only weakly baste. Mereury forms no hydride. 

Certain elements have the same oxidation number in all or almost all their compounds. The Group 1 metals always exist as +1 ions in their compounds and hence are assigned an oxidation number of +1. By the same token, Group 2 elements always have oxidation numbers of +2 in their compounds. Fluorine always has an oxidation number of — 1. 

Am. In each ease, the answer is BuS. Part (ft) gives the ions and their charges, and so is perhaps easiest to answer. Part (know that periodic group IIA elements always form 2-t- ions in all their compounds and that sulfur forms a 2- ion in its compounds with metals. It is also necessary to remember that the metal is named first. In part (< ). the fact that there is only one compound of these two elements is deduced by the fact that the barium is stated with no Roman numeral, and that sulfide is a specific ion with a specific (2-) charge. 

In substitution reactions with acids, metals that can form two different ions in their compounds generally form the one with the lower charge. For example, iron can form Fe2+ and Fe3+. In its reaction with HCI, FeCI2 is formed. In contrast, in combination with the free element, the higher-charged ion is often formed if sufficient nonmetal is available. 

A significant portion of the universe is comprised of elements, ions, and the compounds formed by their combinations - in effect, chemistry on the grandest scale possible. These chemical components can occur as gases or superheated plasmas, less commonly as solids, and very rarely as liquids. 

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