Bond/Bonding stable octet

The apparent inertness of the noble gases gave them a key position in the electronic theories of valency as developed by G. N. Lewis (1916) and W. Kossel (1916) and the attainment of a stable octet was regarded as a prime criterion for bond formation between atoms (p. 21). Their monatomic, non-polar nature makes them the most nearly perfect gases known, and has led to continuous interest in their physical properties. 

We know that the electronegativity difference between atoms must be greater than 1.9 to form an ionic bond. But if the electronegativity values of the atoms are similar, the tendency of the atoms to take or give electrons will also be similar. The transfer of electrons is not possible between such atoms, so the atoms must share electrons to gain a stable octet. The bond that is formed as a result of electron sharing is called a covalent bond. Covalent bonds are generally formed between two nonmetals. 

Carbon has four bonding electrons and can attain a stable octet of electrons by bonding to four other atoms, i.e. it has a valency of four. 

Lewis and many other chemists had recognized the shortcomings of the ionic bond. When diatomic molecules, such as or Cl, were considered, there was no reason why one atom should lose an electron and an identical atom should gain an electron. There had to be another explanation for how diatomic molecules formed. We have seen how the octet rule applies to the formation of ionic compounds by the transfer of electrons. This rule also helps explain the formation of covalent bonds when molecules (covalent compounds) form. Covalent bonds result when atoms share electrons. Using fluorine, F, as a representative halogen, we can see how the octet rule applies to the formation of the molecule. Each fluorine atom has seven valence electrons and needs one more electron to achieve the stable octet valence configuration. If two fluorines share a pair of electrons, then the stable octet configuration is achieved ... 

Examples of neutral Lewis acids are halides of group 3A elements, such as BF3. Boron trifluoride, a colorless gas, is an excellent Lewis acid because the boron atom in the trigonal planar BF3 molecule is surrounded by only six valence electrons (Figure 15.12). The boron atom uses three sp2 hybrid orbitals to bond to the three F atoms and has a vacant 2p valence orbital that can accept a share in a pair of electrons from a Lewis base, such as NH3. The Lewis acid and base sites are evident in electrostatic potential maps, which show the electron poor B atom (blue) and the electron rich N atom (red). In the product, called an acid-base adduct, the boron atom has acquired a stable octet of electrons. 

Atoms form bonds that allow them to acquire a stable octet (or eight valence electrons). 

Draw Lewis structures to show how each pair of elements in question 4 forms bonds to achieve a stable octet. 

Double bonds can form between different elements, as well. For example, consider what happens when carbon bonds to oxygen in carbon dioxide. To achieve a stable octet, carbon requires four electrons, and oxygen requires two electrons. Hence, two atoms of oxygen bond to one atom of carbon. Each oxygen forms a double bond with the carbon, as shown in Figure 3.18. 

They do not have enough valence electrons to achieve stable octets by sharing electrons. Although metals do not form covalent bonds, however, they do share their electrons. 

Because C is in Group 4 of the periodic table and gains its stable octet only by sharing electrons, i.e. covalent bonding. 

An element with an octet of valence electrons, such as that found in the noble gas Ne, has a stable configuration. When two chlorine atoms form a covalent bond, each atom contributes one electron to a shared pair. With this shared pair, both atoms can have a stable octet. This tendency of bonded atoms to have octets of valence electrons is called the octet rule. 

Carbon, oxygen, and nitrogen atoms often form double bonds by sharing two pairs of electrons. Carbon and nitrogen atoms may even share three pairs of electrons to form a triple bond. Think about the molecule N2. With five valence electrons, each N atom needs three more electrons for a stable octet. Each N atom contributes three electrons to form three bonding pairs. The two N atoms form a triple bond by sharing these three pairs of electrons, or a total of six electrons. Because the two N atoms share the electrons equally, the triple bond is a nonpolar covalent bond. 

The type of bonding found in metals is quite different from that in other crystals. As we compare the various main group and transition metals in the periodic table we see only small differences in electronegativity. So, there is little tendency for ionic bonding in metals. The electronic configurations of metal atoms, even in the transition metals, do not have nearly-filled subshells, so there is little tendency to form covalent bonds by sharing electrons to achieve a stable octet. The familiar classical models of chemical bonding (see Chapter 3) do not extend to metals. 

It has already been shown that the F2 molecule involves a single covalent bond. If the two O atoms of O, are treated in the same way they have insufficient valence shell electrons to form stable octets by sharing just one electron pair, but if two electron pairs are shared, stable octets are formed on both O atoms, with the sharing of the two electron pairs. This situation is referred to as a double bond ... 

According to this rule an atom which has (8 - n) electrons can only form n covalent bonds - thus completing its stable octet of electrons in the valence shell. 

To obtain a stable octet of electrons, the carbon atom needs four more electrons, and each oxygen atom needs two more electrons. Therefore, each oxygen atom must share two pairs of electrons with the carbon atom. A bond formed by sharing two pairs of electrons between two atoms is called a double bond, as illustrated by the electron dot structure for carbon dioxide. 

Electron Configuration, and the Periodic Table Ionic bonding involves the complete transfer of electrons between two atoms of widely different electronegativities charged ions are formed (one positive from the loss of electrons and one negative from the gain of electrons), both of which usually have a stable octet outer shell. The ionic bond results from the attraction between the positive cation and negative anion. 

The carbon in CH4 has a stable octet and all eight electrons are expressed as four bonding electron pairs. In NH3, the nitrogen has a stable octet but, since... 

Lewis acid /h>o-is/ A substance that can accept an electron pair to form a coordinate bond a Lewis base is an electron-pair donor. In this model, the neutralization reaction is seen as the acquisition of a stable octet by the add, for example ... 

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