Noble gases electron arrangement

Clearly the explanation of the chemical bond given by Kossel cannot apply to homonuclear molecules such as CI2. Almost simultaneously with the publication of Kossel s theory, Lewis published a theory that could account for such molecules. Like Kossel, Lewis was impressed with the lack of reactivity of the noble gases. But he was also impressed by the observation that the vast majority of molecules have an even number of electrons, which led him to suggest that in molecules, electrons are usually present in pairs. In particular, he proposed that in a molecule such as CI2 the two atoms are held together by sharing a pair of electrons because in this way each atom can obtain a noble gas electron arrangement, as in the following examples ... 

Examine the relationship between ion charge and noble gas electron arrangement. 

Lewis assumed that the pair of electrons was one of the stable arrangements, so that apart from the formation of noble gas electron arrangements, atoms having unpaired electrons would form bonds. This he calls the rule of two, to distinguish it from the rule of eight. Both rules are explicit in his theory. 

Atoms can also achieve noble-gas electron arrangements by the transfer of electrons from one atom to another. This process is also an integral part of Lewis theory. The process produces opposite... 

These ions have stable noble gas electron arrangements the sodium ion has the electron arrangement of neon and the chloride ion has the electron arrangement of argon. 

In the case of the elements oxygen and nitrogen, two and three pairs of electrons respectively must be shared between the two atoms of their molecules to achieve a stable noble gas electron arrangement. The oxygen molecule has a double bond and the nitrogen molecule has a triple bond (Figure 4.26). 

State the number of electrons that must be lost by atoms of each of the following to achieve a noble gas electron arrangement ... 

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. 

Lewis structures are drawn to represent the arrangement of the valence electrons in a molecule. The rules for drawing Lewis structures are based on the observation that nonmetal atoms tend to achieve noble gas electron configurations by sharing electrons. This leads to a duet rule for hydrogen and to an octet rule for many other atoms. 

Bonding between atoms to form a molecule Involves only the outermost electrons of the atoms, so only these valence electrons are shown in the Lewis structures of molecules. The most important requisite for the formation of a stable compound is that each atom of a molecule attain a noble gas electron configuration. In Lewis stmctures, arrange the bonding and nonbonding valence electrons to try to complete the octet (or duet) for as many atoms as possible. 

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 ... 

It says that atoms will gain or lose sufficient electrons to achieve an outer electron arrangement identical to that of a noble gas. This arrangement usually consists of eight electrons in the valence shell. 

In essence, two H atoms move close enou to each other to sham the electron pair. Although there are still two atoms and just two electrons, this arrangemait allows each H atom to count both electrons as its own and to feel as though it has the noble gas electron configuration of helium. This type of arrangement, where two atoms share a pair of electrons, is known as covalent bonding, and the shared pair of electrons constitutes the covalent bond. In a covalent bond, each electron in a shared pair is attracted to the nuclei of both atoms. It is this attraction that holds the two atoms together. 

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. 

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