Nonmetals electrons added

Ionize (anion) Attach electron(s) to the gaseous nonmetal atom to form the gaseous anion. Several electron affinity values may be required. Recall that for electron gain, A//= - ea for each electron added. 

That this principle is a reasonable one may be seen by the consideration of values of the ionization energy and electron affinity of atoms. The electron affinity of atoms of nonmetals is about 350 kJ mole for the first electron added, to convert the atom F - into the anion F . or the atom 0- into the anion 0- (Section 6-9). But there is in general no significant affinity for a second electron to convert 0- into —. 

Nonmetal electrodes are most often fabricated by pressing or rolling of the solid in the form of fine powder. For mechanical integrity of the electrodes, binders are added to the active mass. For higher electronic conductivity of the electrode and a better current distribution, conducting fillers are added (carbon black, graphite, metal powders). Electrodes of this type are porous and have a relatively high specific surface area. The porosity facilitates access of dissolved reactants (H+ or OH ions and others) to the inner electrode layers. 

Electron affinity is conventionally defined as the energy released when an electron is added to the valence shell of an atom. Unfortunately, this is in contradiction to the universal thermodynamic convention that enthalpies of exothermic reactions shall be assigned negative signs. Since it seems impossible to overthrow the election affinity convention at this late date without undue confusion, one can adopt one of two viewpoints to minimize confusion. One is to let the electron affinities of the most active nonmetals be positive, even though in thermodynamic calculations the enthalpies are negative ... 

Malleable materials can be beaten into sheets. Ductile materials can be pulled into wires. Lustrous materials have a shine. Oxides, hydrides, and halides are compounds with 0, H, and halogens respectively. Measures of intermolecular attractions other than melting point are also higher for metal oxides, hydrides, and halides than for the nonmetal compounds. A dopant is a small quantity of an intentionally added impurity. The controlled movement of electrons in doped silicon semiconductors carries digital information in computer circuitry. 

Think of forming an ionic compound as three steps (this is a simplification, as with all models) (1) removing an electron from the metal (2) adding an electron to the nonmeral and (3) allowing the metal cation and nonmetal anion to come together. 

Chlorine, a Group VILA nonmetal, has a single vacancy in its valence shell. Adding one electron to chlorine fills this vacancy and forms a chloride ion, Cl , which has the stable argon configuration. The seven valence electrons in chlorine are underlined. 

Electron affinity (EA) is a measure of the energy change that occurs when an electron is added to the valence shell of an atom. Some selected values of Eea for nonmetals are listed in Table 2.5. The addition of the first electron is usually exothermic (e.g., oxygen, sulfur) further additions, when they occur, are by necessity endothermic since the second electron is now approaching a negatively charged entity. The electron affinity of Cl is - 348.7 kJ/mol. 

Nonmetal ions As shown in Table 7.3, nonmetals gain the number of electrons that, when added to their valence electrons, equals 8. For example, consider phosphorus, with five valence electrons. To form a stable octet, the atom gains three electrons and forms a phosphide ion with a 3- charge. Likewise, oxygen, with six valence electrons, gains two electrons and forms a oxide ion with a 2- charge. 

Similarly, adding electrons to nonmetals is either exothermic or only slightly endothermic as long as the electrons are added to the valence shell. Thus, a Cl atom easily adds an electron to form Cl, which has the same electron configuration as Ar ... 

To form a Cl ion, the second electron would have to be added to the next higher shell of the Cl atom, an addition that is energetically very unfavorable. Therefore, we never observe CP ions in ionic compounds. We thus expect ionic compounds of the representative metals from groups lA, 2A, and 3A to contain H-, 2-I-, and 3-t- cations, respectively, and usually expect ionic compounds of the representative nonmetals of groups 5A, 6A, and 7A to contain 3—, 2—, and 1 — anions, respectively. 

Located on the periodic table of the elements in Figure 13-2 is an area between the conductors and insulators, or metals and nonmetals, and are the elements called semiconductors. This area is colored blue. Semiconductors typically contain four electrons in their outer orbit. Materials that are semiconductors include silicon and germanium. As shown in Figure 13-7, the silicon atom has four electrons in its outer orbit. By adding or subtracting electrons, engineers can modify semiconductors to perform a desired operation. 

In a formal sense, these are oxidation reactions, because rhodium(l) is oxidized to rhodium(ni). These are also addition reactions because two ligands are added to square planar sixteen-electron systems which are transformed into octahedral eighteen-electron complexes. These reactions can also be viewed as an insertion reaction (see (4) below) in which a metal atom is inserted into a bond between two nonmetals. 

Ions are formed by adding or removing electrons from an atom. Atoms do not form ions on their own. Most often ions are formed when metals combine with nonmetals. 

One small group of elements is very interesting. They are not quite metals or nonmetals. They are called metalloids. [These are colored blue in the table on page 32.] Some metalloids, such as silicon, are semiconductors. This means they are poor conductors of electricity when they are pure. However, when small amounts of other materials are added, they can conduct electricity. Silicon and other semiconductors are the basis of microchips and other electronic devices. 

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