Cation from metal atoms

When an alkali metal contacts water, metal atoms donate electrons to water molecules, producing hydrogen gas and a solution of the metal cation (for example, Na ). When a metal such as Ca, Zn, or Fe is treated with a strong aqueous acid, hydronium ions in the acid solution accept electrons from metal atoms, creating cations that then dissolve. We describe these redox reactions in Chapter 4. Zinc metal, for example, reacts with hydrochloric... 

Cations are generally metallic radicals obtained by loss of electrons from metal atoms (M (metal) — M + (cation) + ne (electrons)), while anions are nonmetallic ions or radicals (a group of atoms of two or more elements) obtained by the acquisition of electrons by nonmetallic atoms (A (nonmetal) + me —> Am (anion). 

Nonmetal atoms accept electrons from metal atoms if the metal atoms are available, or else they share electrons they never donate electrons to form monatomic cations. The largest charge on any monatomic cation is 4 -I-, and on any monatomic anion, it is 3 —. 

In Section 2.5 we learned that ionic compounds are made up of cations (positive ions) and anions (negative ions). With the important exception of the ammonium ion, NH4, all cations of interest to us are derived from metal atoms. Metal cations take their names from the elements. For example ... 

Formally, this prototype reaction serves for cations as well as anions. Cations by definition always have positive Z values and derive from metal atoms. As an example of this, the following reaction, which would apply to the zirconium constituent in the well known solid electrolyte calcia-stabilized zirconia (CSZ), may be cited... 

Also listed in Table 2 is 8, equal to the differences in bond valence for the bonds from metal atoms to 0(1) and 0(2). The larger the value of 8, the less stable the compound is expected to be on the basis of Pauling s rule (as restated above). One would expect that if all other factors were equal (i.e. no specific preference for octahedral or tetrahedral coordination), distributions with valences of ABC = 152 or 161 would be less stable than 125 or 116 - i.e. there is a site preference that depends on the valences of the other cations in the structure as well as an intinsic site preference of individual atoms. If the compound can be made, the larger the value of 8, the greater the distortion expected in the oxygen polyhedra surrounding the metal atoms. 8 is in fact proportional to the difference in valence of the two octahedrally-coordinated metal atoms so that the compounds with large 8 are also those most likely to be ordered. 

The species resulting from the hydrolysis of hydrated cations such as those mentioned here are often highly complex, containing more than one metal atom (i.e. they may be polynuclear). The description here is simplified to show the essentials of the processes. 

Two types of chemical bonds, ionic and covalent, are found in chemical compounds. An ionic bond results from the transfer of valence electrons from the atom of an electropositive element (M) to the atom(s) of an electronegative element (X). It is due to coulombic (electrostatic) attraction between the oppositely charged ions, M (cation) and X (anion). Such ionic bonds are typical of the stable salts formed by combination of the metallic elements (Na, K, Li, Mg, etc.) with the nonmetallic elements (F, Cl, Br, etc.). As an example, the formation of the magnesium chloride molecule from its elemental atoms is shown by the following sequence ... 

Heterogeneities associated with a metal have been classified in Table 1.1 as atomic see Fig. 1.1), microscopic (visible under an optical microscope), and macroscopic, and their effects are considered in various sections of the present work. It is relevant to observe, however, that the detailed mechanism of all aspects of corrosion, e.g. the passage of a metallic cation from the lattice to the solution, specific effects of ions and species in solution in accelerating or inhibiting corrosion or causing stress-corrosion cracking, etc. must involve a consideration of the detailed atomic structure of the metal or alloy. 

When an atom loses or gains electrons, charged particles called ions are formed. Metal atoms typically tend to lose electrons to form positively charged ions called cations (pronounced CAT-i-ons). Examples include the Na+ and Ca2+ ions, formed from atoms of the metals sodium and calcium ... 

In most of these examples, the chiral auxiliary is introduced to the allylic reagent at a very late stage in the synthesis of the precursor, thus providing a facile access. It is obvious that in most examples, the central metal atom is kept from becoming stereogenic, and in addition, a C2-symmet-ric cation is desirable, in order to minimize the possible number of competing transition states. 

The ionic model describes a number of metal halides, oxides, and sulfides, but it does not describe most other chemical substances adequately. Whereas substances such as CaO, NaCl, and M 2 behave like simple cations and anions held together by electrical attraction, substances such as CO, CI2, and HE do not. In a crystal of Mgp2, electrons have been transferred from magnesium atoms to fluorine atoms, but the stability of HE molecules arises from the sharing of electrons between hydrogen atoms and fluorine atoms. We describe electron sharing, which is central to molecular stability, in Chapters 9 and 10. 

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