Noble-gas core

The electronic configuration for an element s ground state (Table 4.1) is a shorthand representation giving the number of electrons (superscript) found in each of the allowed sublevels (s, p, d, f) above a noble gas core (indicated by brackets). In addition, values for the thermal conductivity, the electrical resistance, and the coefficient of linear thermal expansion are included. 

In general, we can think of an atom of any element as having a noble-gas core surrounded by a number of electrons in the valence shell, the outermost occupied shell. The valence shell is the occupied shell with the largest value of n. 

In some cases, it would be convenient to condense the electron configuration. In this condensed form, the electronic configuration of the previous noble gas forms a core represented by the atomic symbol of the element enclosed in brackets (i.e., [He] or [Ne]). The electrons added since the noble gas, follow the noble gas core. For example, cobalt can be represented as an argon core plus the 4s and 3d electrons. Thus, ls22s22p63s23p64s23d7 becomes [Ar]4s23d7. 

The electrons that are contained in the noble gas core are the core electrons while the electrons outside the core are valence electrons. These valence electrons are involved in the chemical behavior of the elements. For the representative elements, the valence electrons are those s and p electrons in the outermost energy level. The valence shell contains the valence electrons. 

Aluminum loses three valence electrons to form the Al3+ ion, which has the same electron configuration as neon. When the atoms of metals on the left of the p block in Periods 4 and higher lose their s- and p-elec-trons, they leave a noble-gas core surrounded by an additional, complete subshell of d-electrons. For instance, gallium forms the ion Ga3+ with the configuration [Ar]3d10. The d-electrons of the p-block atoms are gripped tightly by the nucleus and, in most cases, cannot be lost. We saw in Section 1.18 that the inert-pair effect implies that the elements listed in Fig. 1.44 can lose either their valence p-electrons alone or all their valence p- and s-electrons. 

The closely related elements lithium, sodium, potassium, rubidium, and cesium, often termed the alkali metals, have a single s electron outside a noble gas core. Some relevant data are listed in Table 3-1. 

Fundamental atomic and physical properties of the alkali metals are given in Tables 1, 2, and 3. The elements are characterized by having electron configurations each with a single s orbital electron outside a noble gas core (see Table 1). Sodium and cesium are mononucUdic so that their relative atomic masses are known extremely accurately in effect, the same can be written for potassium and rubidium since their isotopes (of which there are three and two, respectively) have... 

Cr(CO)e A Cr atom has 6 electrons outside its noble gas core. Each CO is considered to act as a donor of 2 electrons. The total electron count is therefore ... 

Pentahapto-C5H5 is considered by this method as CsHs , a donor of 3 electron pairs it is a 6-electron donor. As in the first example, CO is counted as a 2-electron donor. Chloride is considered CF, a donor of 2 electrons. Therefore, (if) -C5H5)Fe(CO)2Cl is formally an iron(II) complex. Iron(II) has 6 electrons beyond its noble gas core. Therefore, the electron count is Fe(n) 6 electrons... 

For (Tf) -C5H5)Fe(CO)2Cl, an iron atom has 8 electrons beyond its noble gas core. r) -C5H5 is now considered as if it were a neutral ligand (a 5-electron tt system), in which case it would contribute 5 electrons. CO is a 2-electron donor and Cl (counted as if it were a neutral species) is a 1-electron donor. The electron count is... 

Form cations by losing electrons down to the noble-gas core... 

A chromium atom has six electrons outside its noble gas core. For transition metals the only electrons that are counted are the 5 and d electrons beyond the noble gas core. Each CO is considered to act as a donor of 2 electrons (from an electron dot standpoint, C=0 , the donated electrons correspond to the lone pair on carbon). Thus, the total electron count is... 

The metals in Group IIA have two valence electrons, both in an s-subshell outside the stable noble gas core. It should not be surprising that each forms an ion with a 2+ charge, the result of losing both valence electrons. Be2+, Mg2+, and Ca2+ each have the stable electronic configuration of a noble gas. The l[Kr]3d °) configuration of the strontium ion, Srz+, with a completely tilled 3d-subshell outside the [Kr] noble gas core, is called a pseudo-noble gas core. Pseudo-noble gas cores are very stable, too. Don t be confused by this. Focus on the valence electrons, those in the highest occupied principal shell, the n = 5 shell in strontium. They are the chemically important electrons. 

The metals of the first transition series have a partially filled 3d-subshell and a filled 4s-subshell outside the noble gas core of argon. Because the 3d-subshell is partially filled, both the 3d- and 4s-electrons are involved in the chemistry of these elements. The electronic configurations of vanadium, iron, and nickel are shown below. Each forms a 2+ ion by losing two outermost 45-electrons. Vanadium and iron can also form a 3+ ion by losing an additional 3d-electron. 

Valence electrons are those in the highest occupied energy level of an atom that are directly involved in the chemistry of the element. Alternatively, they are the electrons outside the noble gas core of the atom. 

Line spectrum, p. 250 Many-electron atom, p. 261 Noble gas core, p. 274 Node, p. 255 Paramagnetic, p. 269... 

Explain what is meant by a noble gas core. Write the electron configuration of a xenon core. 

What is the noble gas core How does it simplify the writing of electron configurations ... 

Noble gas core. The noble gas element that most nearly precedes the element being considered. (7.10)... 

The partial (valence-level) electron configuration for the cf-block elements excludes the noble gas core and the filled inner / sublevel ... 

Note that the electron configurations for the larger atoms can get rather cumbersome, but they can be readily shortened by using the noble gas core convention. 

The noble gas core represents all electrons contained in an atom of noble gas. The similar chemical properties of the elements in the 5A group is attibuted to the similar arrangement of the outer shell electrons of all the members of the group ns np. The outermost shell is vital for determining the chemical properties of the elements and is called the valence shell. Similar regularities appear in the other groups of the periodic table. 

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