The Ions That Elements Form

Identify which of the following elements experience the inert-pair effect and write the formulas for the ions that they form (a) Sb (b) As (c) Tl (d) Ba. 

These diagrams show the ions that are formed from neutral atoms of sodium, magnesium, sulfur, and chlorine. What other element has the same electron arrangement that sodium, magnesium, sulfide, and chloride ions have ... 

The periodic table shown in Figure 7.14 contains elements labeled A-G. For each labeled element, state the number of valence electrons and identify the ion that will form. 

A transition metal is one of the elements in the skinny central part of the Periodic Table, and includes iron (Fe), chromium (Cr, this name anticipates the colour to come as chroma is the Greek word for colour), cobalt (Co), and nickel (Ni). The ions these elements form, such as Fe and Co, are commonly found surrounded by and bonded to six small molecules and ions that have an independent existence, such as H O, NH, and CN". These species are called ligands and the complete clusters are... 

The periodic table can help us decide what type of ion an element forms and what charge to expect the ion to have. Fuller details will be given in Chapter 2, but we can begin to see the patterns. One major pattern is that metallic elements— those toward the left of the periodic table—typically form cations by electron loss. Nonmetallic elements—those toward the right of the table—typically form anions by gaining electrons. Thus, the alkali metals form cations, and the halogens form anions. 

Many of the d-block elements form characteristically colored solutions in water. For example, although solid copper(II) chloride is brown and copper(II) bromide is black, their aqueous solutions are both light blue. The blue color is due to the hydrated copper(II) ions, [Cu(H20)fJ2+, that form when the solids dissolve. As the formula suggests, these hydrated ions have a specific composition they also have definite shapes and properties. They can be regarded as the outcome of a reaction in which the water molecules act as Lewis bases (electron pair donors, Section 10.2) and the Cu2+ ion acts as a Lewis acid (an electron pair acceptor). This type of Lewis acid-base reaction is characteristic of many cations of d-block elements. 

The electrochemical preparation of metal chalcogenide compounds has been demonstrated by numerous research groups and reviewed in a number of publications [ 1-3]. For the most part, the methods that have been used comprise (a) cathodic co-reduction of the metal ion and a chalcogen oxoanion in aqueous solution onto an inert substrate (b) cathodic deposition from a solvent containing metal ions and the chalcogen in elemental form (the chalcogens are not soluble in water under normal conditions, so these reactions are carried out in non-aqueous solvents) (c) anodic oxidation of the parent metal in a chalconide-containing aqueous electrolyte. 

The elements that form only one cation are the alkali metals (group IA), the alkaline earth metals (group IIA), zinc, cadmium, aluminum, and most often silver. The charge on the ions that these elements form in their compounds is always equal to their periodic table group number (or group number minus 10 in the newest labeling system in the periodic table). 

You may have noticed the ring that sometimes forms around the 1 tub when you take a bath. This ring is formed because the positively charged Mg+2 and Ca+2 ions that are dissolved in the water found in many localities have combined with elements in the soap to form compounds which will not dissolve in water. The insoluble compounds thus formed float to the sides of the tub and are deposited in the form of a ring. 

Based on their positions on the periodic table assign charges to the ions that the elements in question 29 might form. 

Fig. 16.12. Subunit structure of the acetylcholine receptor, a) The acetylcholine receptor has the subunit structure 02 7 - The four transmembrane elements Ml—M4 are shown for the y subunit. The binding sites for acetylcholine (ACh) are located on the a-subunits. b) It is assumed that the inner wall of the ion pore is formed by M2 helices of the five subunits, c) Postulated configuration of the M2 helices in the narrowest region of the ion channel. In the closed state, five leucine residues (one per subunit) lie in the ion channel and hinder passage of ions. Above and below the block, there are negatively charged residues that serve as prefilters for ion passage.

In introductory chemistry courses, much emphasis is necessarily placed on the concept of stoichiometry, that is, the fact that elements combine in certain definite proportions by weight, proportions that reflect their valences and atomic masses. For much of the chemistry of the main group elements and organic compounds, this concept works extremely well, but in transition metal chemistry in particular it is common for ions of more than one oxidation state to form with comparable ease, and sometimes to occur together in the same ionic solid. The presence of more highly oxidized cations... 

Work on potential pollution sources requires a thorough knowledge of the composition of potential pollutants. Maximum parameters should be measured on every industrial effluent that leaves a factory and the fluid that is formed in each landfill. The parameters to be measured include temperature, pH, major dissolved ions, trace elements (mainly metals and metal compounds), organic compounds, and isotopic compositions of hydrogen, oxygen, carbon, sulfur, and nitrogen. To perform such analyses, special laboratories have to be contacted. In certain cases the main product may serve as the label, and in other cases the labels are supplied by accompanying compounds, which in themselves may not be poisonous. 

Metals have very low electron affinities. This is especially true for the Group 1 (IA) and 2 (IIA) elements. Atoms of these elements form stable positive ions. A negative ion that is formed by the elements of these groups is unstable. It breaks apart into a neutral atom and a free electron. 

The favored hypothesis regarding why cells within the same organism biomineralize with different minerals, e.g., calcite and aragonite in bivalves, is that there are different organic moieties which lead to changed nucleation opportunities. For example, permeability of a vacuole membrane in plants may lead to different concentrations of the ions and elements within, or to the inclusion of inhibitors that prevent nucleation of a specific mineral forms (Goodwin and Mercer, 1982). 

Csl(5) + LiF(.9) is exothermic (AH = —146 kJ/raol) because of the large lattice enthalpy of LiF. This is contrary to the simple electronegativity argument that the most electropositive and the most electronegative elements form the most stable compounds. However, these same compounds fit the hard-soft arguments, with LiF, the hard-hard combination, and Csl, the soft-soft combination, the least soluble salts (Section 6-3). Sometimes these factors are also modified by particular interactions because of the electronic structures of the ions. 

The rate of sedimentation is controlled largely by the rate at which an element is converted (uptake by organisms, precipitation, coprecipitation, ion exchange) into an insoluble, setdeable form. Hence the reactivity of the elements influences the time that elements spend, on the average, as constituents of the seawater. For most elements residence times have been determined on the basis of estimates of the input by runoff from the land or from calculations of sedimentation times. Remarkably similar results are obtained by these two... 

Suppose you are given a clear aqueous solution and told that it could contain almost any of the ions formed by the common metalhc elements. Your job is to find out which ions the solution contains. It seems an impossible task, but chemists have worked out a scheme that allows you to separate and identify many common metal ions. The scheme is based upon the differing solubilities of the ions. For example, only three ions form insoluble chlorides—Ag+, Pb, and Hg2. That may give you an idea of how you could proceed. If you add HCl to your solution, those three ions will precipitate as a white solid that would contain AgCl(s), PbCl2(s), and Hg2Cl2(s) if all three of the metal ions are present. The ions that do not form insoluble chlorides will be left in the clear solution, which can be separated from the white sohd. 

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