Noble gases electronic structure

This is reasonable noble-gas atoms must have an extremely stable electronic structure, because they are so unreactive. Other atoms might be expected to acquire noble-gas electronic structures by losing or gaining electrons. 

These examples illustrate the principle that atoms in covalently bonded species tend to have noble-gas electronic structures. This generalization is often referred to as the octet rule. Nonmetals, except for hydrogen, achieve a noble-gas structure by sharing in an octet of electrons (eight). Hydrogen atoms, in molecules or polyatomic ions, are surrounded by a duet of electrons (two). 

The effect of cation type on the magnitude of the log K value for metal-complex formation may be found by comparing cations of the same charge and similar ionic radii having noble gas electronic structures with those having pseudo-noble gas and pseudo-noble gas +ns2 electronic structures. Also, comparisons should be made in the region of optimum stability for the cations involved. The data in Table 3 show such com-... 

A cation is a positively charged ion formed when an atom loses one or more electrons. Most cations are metallic and have the same name as the metallic element. For example, when lithium (Li) loses an electron, a lithium ion (Li+) is formed. Lithium is in group 1 and needs to lose one electron to acquire the noble gas electron structure of helium (FFe), the closest noble gas. 

Relation of ionic valence to noble-gas electronic structures. 

Values are expressed in kilojoules per mole, showing energies required to remove 1 to 5 electrons per atom. Blue t) e indicates the energy needed to remove an electron from a noble gas electron structure. 

The chemical reaction between sodium and chlorine is a very vigorous one, producing considerable heat in addition to the salt formed. When energy is released in a chemical reaction, the products are more stable than the reactants. Note that in NaCI both atoms attain a noble gas electron structure. 

Study the following examples. Note the loss and gain of electrons between atoms also note that the ions in each compound have a noble gas electron structure. 

These arrangements are Lewis structures because each atom has a noble gas electron structure. Note that the shape of the molecule is not shown by the Lewis structure. 

Now consider the most common situation (CH4), with four pairs of electrons on the central carbon atom. In this case the central atom exhibits a noble gas electron structure. What arrangement best minimizes the electron pair repulsions At first, it seems that an obvious choice is a 90° angle with all the atoms in a single plane ... 

Carbon has four valence electrons it needs four electrons to form a noble gas electron structure. By sharing four electrons, a carbon atom can form four covalent bonds. 

In this reaction, Na atoms lose one electron each to form Na ions, which contain only ten electrons, the same number as the preceding noble gas, neon. We say that sodium ions have the noble gas electronic structure of neon Na is isoelectronic with Ne. In contrast. Cl atoms gain one electron each to form Q ions, which contain 18 electrons. This is the same number as following noble gas, argon CL is isoelectronic with Ar. These processes can be represented compactly as... 

In Summary There are two extreme types of bonding, ionic and covalent. Both derive favorable energetics from Coulomb forces and the attainment of noble-gas electronic structures. Most bonds are better described as something between the two types the polar covalent (or covalent ionic) bonds. Polarity in bonds may give rise to polar molecules. The outcome depends on the shape of the molecule, which is determined in a simple manner by arrangement of its bonds and nonbonding electrons to minimize electron repulsion. 

The electrovalent bond is formed by electrostatic attraction between oppositely charged ions. Thus Na, with one outer electron, loses this electron to achieve the noble gas Ne structure, while Cl with seven outer electrons, gains one electron to achieve the Ar structure. 

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 ... 

Each atom has achieved a noble gas electron configuration. Thus, you can be confident that this is a reasonable Lewis structure. 

The Lewis structure of a molecule represents the arrangement of valence electrons among the atoms in the molecule. These representations are named after G. N. Lewis (Fig. 13.13). The rules for writing Lewis structures are based on the observations of thousands of molecules, which show that in most stable compounds the atoms achieve noble gas electron configurations. Although this is not always the case, it is so common that it provides a very useful place to start. 

We have already seen that when metals and nonmetals react to form solid binary ionic compounds, electrons are transferred and the resulting ions typically have noble gas electron configurations. An example is the formation of KBr, where the K ion has the [Ar] electron configuration and the Br- ion has the [Kr] electron configuration. In writing Lewis structures, the rule is that... 

Thus bond formation can be envisaged as a result of attaining noble-gas-type structures that have particularly stable configurations of electrons. Symbolically this covalent bond is written F-F. We can think of the bonding electrons, which tend to sit between the two nuclei, as shielding the repulsive forces of the protons in the nucleus. 

Next, we will consider Lewis structures for molecules with covalent bonds involving nonmetals in the first and second periods. The principle of achieving a noble gas electron configuration applies to these elements as follows ... 

Remember that when writing Lewis structures, you don t have to worry about which electrons come from which atoms in a molecule. It is best to think of a molecule as a new entity that uses all of the available valence electrons from the various atoms to achieve the strongest possible bonds. Think of the valence electrons as belonging to the molecule, rather than to the individual atoms. Simply distribute the valence electrons so that noble gas electron configurations are obtained for each atom, without regard to the origin of each particular electron. 

The idea that covalent bonding can be predicted by achieving noble gas electron configurations for all atoms is a simple and very successful idea. The rules we have used for Lewis structures describe correctly the bonding in most molecules. However, with such a simple model, we should expect some exceptions. Boron, for example, tends to form compounds in which the boron atom has fewer than eight electrons around it—that is, it does not have a complete octet. Boron trifluoride, BF3, a gas at normal temperatures and pressures, reacts very energetically with molecules such as water and ammonia that have unshared electron pairs (lone pairs). 

Even though there are exceptions, most molecules can be described by Lewis structures in which all the atoms have noble gas electron configurations, and this is a very useful model for chemists. 

The rules for drawing Lewis structures recognize the importance of noble gas electron configurations. 

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