Valence electrons, 2, 3 Table

Write out the electron configuration of sodium, magnesium, and aluminum and find the ionization energies for all their valence electrons (Table 20-IV, p. 374). Account for the trend in the heats of vaporization and boiling points (Table 20-1) of these elements. Compare your discussion with that given in Section 17-1.3. 

The metal centres in the iron, ruthenium, and osmium alkynyl complexes listed in Table 1 possess 18 valence electrons. Table 2 contains HRS data at 1.064 p,m and two-level-corrected values for similar 18 valence electron alkynyl and chloro nickel complexes, and a particularly efficient example is illustrated in Figure 5. These data are substantially resonance enhanced, although the relative orderings are maintained with two-level-corrected values. 

Electrons in iimer shells (those below the outermost shell) are called core electrons. Core electrons do not participate in chemical bonding. Electrons in the outermost shell are called valence electrons, and the outermost shell is called the valence shell. Carbon, for example, has two core electrons and four valence electrons (Table 1.2). 

Eluorine has seven valence electrons (Table 1.2). Consequently, it readily acquires an electron in order to have an outer shell of eight electrons. When an atom acquires an electron, energy is released. Elements in the same column as fluorine (e.g., chlorine, bromine, and iodine) also need only one electron to have an outer shell of eight, so they, too, readily acquire an electron. Elements that readily acquire an electron are said to be electronegative—they acquire an electron easily and thereby become negatively charged. 

Knowing that nitrogen has five valence electrons (Table 1.2), convince yourself that the appropriate formal charges have been assigned to the nitrogen atoms in the following Lewis stractures ... 

Carbon has two core electrons and four valence electrons (Table 1.2). Lithium and sodium each have one valence electron. If you examine the periodic table inside the back cover of this book, you will see that lithium and sodium are in the same column. Elements in the same column of the periodic table have the same number of valence electrons. Because the number of valence electrons is the major factor determining an element s chemical properties, elements in the same column of the periodic table have similar chemical properties. Thus, the chemical behavior of an element depends on its electronic configuration. 

For example, an oxygen atom has six valence electrons (Table 1.2). In water (H2O), oxygen owns six electrons (four lone-pair electrons and half of the four bonding electrons). Because the number of electrons it owns is equal to the number of its valence electrons (6 - 6 = 0), the oxygen atom in water does not have a formal charge. 

You may be surprised to learn that carbon forms four covalent bonds, since you know that carbon has only two unpaired valence electrons (Table 1.2). But if carbon formed only two covalent bonds, it would not complete its octet. We need, therefore, to come up with an explanation that accounts for the observation that carbon forms four covalent bonds. 

The nitrogen atom in ammonia (NH3) forms three covalent bonds. Nitrogen s electronic configuration shows that it has three unpaired valence electrons (Table 1.2), so it does not need to promote an electron to form the three covalent bonds required to achieve an outer shell of eight electrons—that is, to complete its octet. 

HF, HCl, HBr, and HI are called hydrogen halides. A halogen has only one unpaired valence electron (Table 1.2), so it forms only one covalent bond. 

Figure 2-61. a) The bonding in organometallic complexes (e.g., ferrocene) cannot be expressed adequately by a connection table, b) A new representation has to account for all the valence electrons of Iron,... 

TABLE 1-9. 7T-BOND ORDERS AND BOND LENGTHS IN ALL-VALENCE-ELECTRONS CALCLn..A-TIONS... 

If IS offen convenienf to speak of the valence electrons of an atom These are the outermost electrons the ones most likely to be involved m chemical bonding and reac tions For second row elements these are the 2s and 2p electrons Because four orbitals (2s 2p 2py 2pf) are involved the maximum number of electrons m the valence shell of any second row element is 8 Neon with all its 2s and 2p orbitals doubly occupied has eight valence electrons and completes the second row of the periodic table... 

An estimate of the hybridization state of an atom in a molecule can be obtained from the group of the periodic table that the atom resides in (which describes the number of valence electrons) and the connectivity (coordination of the atom). The HyperChem default scheme uses this estimate to assign a hybridization state to all atoms from the set (null, s, sp, sp, sp -, and sp ). The special... 

Some excited configurations of the lithium atom, involving promotion of only the valence electron, are given in Table 7.4, which also lists the states arising from these configurations. Similar states can easily be derived for other alkali metals. 

Hafnium [7440-58-6] Hf, is in Group 4 (IVB) of the Periodic Table as are the lighter elements zirconium and titanium. Hafnium is a heavy gray-white metallic element never found free in nature. It is always found associated with the more plentiful zirconium. The two elements are almost identical in chemical behavior. This close similarity in chemical properties is related to the configuration of the valence electrons, and for zirconium and... 

For many species the effective atomic number (FAN) or 18- electron rule is helpful. Low spin transition-metal complexes having the FAN of the next noble gas (Table 5), which have 18 valence electrons, are usually inert, and normally react by dissociation. Fach normal donor is considered to contribute two electrons the remainder are metal valence electrons. Sixteen-electron complexes are often inert, if these are low spin and square-planar, but can undergo associative substitution and oxidative-addition reactions. 

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