Neon, electron configuration

One trend worth noting involves the relative sizes of a set of isoelectronic ions—ions containing the same number of electrons. Consider the ions O2-, F, Na+, Mg2+, and Al3+. Each of these ions has the neon electron configuration. How do the sizes of these ions vary In general, there are two important facts to consider in predicting the relative sizes of ions the number of electrons and the number of protons. Since these ions are isoelectronic, the number of electrons is 10 in each case. Electron repulsions should therefore be about the same in all cases. However, the number of protons increases from... 

Representative elements usually attain stable noble gas electron configurations when they share electrons. In the water molecule eight electrons are in the outer shell of the O atom, and it has the neon electron configuration two electrons are in the valence shell of each H atom, and each has the helium electron configuration. Likewise, the C and O of CO2 and the N of NH3 and the ion each have a share in eight electrons in their outer... 

The 3s and 3p orbitals are filled in going across the third period of the periodic table from sodium through argon. Atoms of these elements, like all atoms beyond neon, have their 10 innermost electrons in the neon electron configuration of ls 2s 2p. Therefore, these atoms have a neon core, which may be designated Ne ... 

Electron configurations of atoms were discussed in some detail in Chapter 3. Emphasis has been placed on the stability of a stable octet of outer shell electrons, which is characteristic of a noble gas. Such an octet is in the ns np electron configuration. The first element to have this configuration is neon, electron configuration WliP lp. (Recall that helium is also a noble gas, but with only 2 electrons, its electron configuration is simply b. ) The next noble gas beyond neon is argon, which has the electron configuration ls 2s 2p 3s 3p, commonly abbreviated NelBs Bp . 

With this notation, the electron configuration of element number 11, sodium may be shown as Ne 35, which is an abbreviation for 15 25 2/7 35. The former notation has some advantage in simplicity, while showing the outer electrons specifically. In the example just cited it is easy to see that sodium has 1 outer shell 35 electron, which it can lose to form the Na ion with its stable noble gas neon electron configuration. 

Note. The electronic configuratioa of any element can easily be obtained from the periodic table by adding up the numbers of electrons in the various quantum levels. We can express these in several ways, for example electronic configuration of nickel can be written as ls 2s 2p 3s 3d 4s. or more briefly ( neon core ) 3d 4s, or even more simply as 2. 8. 14. 2... 

Whether an element is the source of the cation or anion in an ionic bond depends on several factors for which the periodic table can serve as a guide In forming ionic compounds elements at the left of the periodic table typically lose electrons giving a cation that has the same electron configuration as the nearest noble gas Loss of an elec tron from sodium for example yields Na which has the same electron configuration as neon... 

Covalent bonding in F2 gives each fluonne eight electrons in its valence shell and a stable electron configuration equivalent to that of the noble gas neon... 

Caibon has eight electrons in its valence shell in both methane and carbon tetrafluoride. By forming covalent bonds to four other atoms, carbon achieves a stable electron configuration analogous to neon. Each covalent bond in methane and carbon tetrafluoride is quite strong—comparable to the bond between hydrogens in Fl2 in bond dissociation energy. 

As pointed out in Chapter 2, elements close to a noble gas in the periodic table form ions that have the same number of electrons as the noble-gas atom. This means that these ions have noble-gas electron configurations. Thus the three elements preceding neon (N, O, and F) and the three elements following neon (Na, Mg, and Al) all form ions with the neon configuration, is22s22p6. The three nonmetal atoms achieve this structure by gaining electrons to form anions ... 

As you can see, the fluorine atom owns six valence electrons outright and shares two others. Putting it another way, the F atom is surrounded by eight valence electrons its electron configuration has become ls22s22p6, which is that of the noble gas neon. This, according to Lewis, explains why the HF molecule is stable in contrast to species such as H2F, H3F,... none of which exist. 

The periodic table orders the elements in a way that helps chemists understand why atoms behave as they do. What makes fluorine react violently with cesium while its nearest neighbor neon is reluctant to react with anything In other words, what gives the elements their properties and what order lies below the surface of their seemingly random nature Scientists know now that the periodicity of the elements is due largely to recurring patterns in their electron configurations. 

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