Covalent bonding electron sharing and

As we said above, bonds aren t always purely ionic or purely covalent. The best models for ionic bonds include some electron sharing. And covalent bonds don t always share electrons completely evenly. Any difference in electronegativity between bonding nuclei means that the electrons will be attracted more to one nucleus than the other. However, a bond could be considered purely covalent if it is between two identical nuclei, as in hydrogen gas, H2, or oxygen gas, O2. An extreme example of equality in electron sharing is the metallic bond. In a metal, all the atoms are identical and share electrons so readily that the metal can be thought of as one big molecule. 

Ruedenberg K, Schmidt MW (2009) Physical understanding through variational reasoning electron sharing and covalent bonding. J Phys Chem A 113 1954—1968... 

The great American scientist G. N. Lewis coined the word covalent, early in the 20th century. He wanted to express the way that a bond formed by means of electron sharing. Each covalent bond comprises a pair of electrons. This pairing is permanent, so we sometimes say a covalent bond is a formal bond, to distinguish it from weak and temporary interactions such as induced dipoles. 

How does electron sharing lead to bonding between atoms Two models have been developed to describe covalent bonding valence bond theory and molecular orbital theory. Each model has its strengths and weaknesses, and chemists tend... 

The electrons and nuclei in a molecule balance these three interactions in a way that gives the molecule its greatest possible stability. This balance is achieved when the electrons are concentrated between the nuclei. We view the electrons as shared between the nuclei and call this sharing a covalent bond. In any covalent bond, the attractive energy between nuclei and electrons exceeds the repulsive energy arising from nuclear-nuclear and electron-electron interactions. 

For H2 to be a stable molecule, the sum of the attractive energies must exceed the sum of the repulsive energies. Figure 9A shows a static arrangement of electrons and nuclei In which the electron-nucleus distances are shorter than the electron-electron and nucleus-nucleus distances. In this arrangement, attractive interactions exceed repulsive interactions, leading to a stable molecule. Notice that the two electrons occupy the region between the two nuclei, where they can interact with both nuclei at once. In other words, the atoms share the electrons in a covalent bond. 

Read the entire laboratory activity. Form a hypothesis about how to show sharing of electrons in a covalent bond in an illustration and in a model and how the type of bond is determined. Record your hypothesis on page 71. 

When the electrons in a covalent bond are shared equally, the length of the bond between the atoms can be approximated as the sum of the covalent radii. However, when the bond is polar, the bond is not only stronger than if it were purely covalent, it is also shorter. As shown earlier, the amount by which a polar bond between two atoms is stronger than if it were purely covalent is related to the difference in electronegativity between the two atoms. It follows that the amount by which the bond is shorter than the sum of the covalent radii should also be related to the difference in electronegativity. An equation that expresses the bond length in terms of atomic radii and the difference in electronegativity is the Schomaker-Stevenson equation. That equation can be written as... 

There are several, separate types of interaction in III both covalent bonds and dipoles. Induced dipoles involve a partial charge, which we called <5+ or S, but, by contrast, covalent bonds involve whole numbers of electrons. A normal covalent bond, such as that between a hydrogen atom and one of the carbon atoms in the backbone of III, requires two electrons. A double bond consists simply of two covalent bonds, so four electrons are shared. Six electrons are incorporated in each of the rare instances of a covalent triple bond . A few quadruple bonds occur in organometallic chemistry, but we will ignore them here. 

Isoprene (2-methylbuta- 1,3-diene [Structures 7.1a and 7.1b]) is a C5 unit. Structure 7.1a shows the full structural formula where each line between the atoms represents two shared electrons in a covalent bond. In the case of more complex molecules, skeletal structures are used, as in Structure lb, where carbon atoms are normally represented by an intersection of bonds. Carbon-hydrogen bonds are not shown, although all other atoms (O, N, P and so on) are indicated. 

It is easy to see from the examples in the previous section how two identical atoms can share electrons to achieve an octet and form diatomic molecules. Because each of our examples dealt with identical atoms, the electrons can be considered to be shared equally by each atom. The bond formed when the atoms are equally shared can be thought of as a pure covalent bond. But what happens in covalent compounds Remember, a compound contains two different elements. When atoms of two different elements are held together by covalent bonds, there is an unequal sharing of the electrons. The sharing of electrons in a covalent bond may be compared to you and a friend sharing a flashlight while walking down a dark street. If you and your friend both held the... 

Actual molecules do not in any way look like the ball-and-stick models. The sharing of electrons in the covalent bonds requires that the atoms of the molecule overlap as represented in Figure 1-5. However, the ball-and-stick models will suffice for our understanding of structural organic chemistry. 

Flowever, the electrons of a covalent bond are not necessarily shared equally by the bonded atoms, especially when the affinities of the atoms for electrons are very different. Thus, carbon-fluorine and carbon-lithium bonds, although they are not ionic, are polarized such that the electrons are associated more with the atom of higher electron affinity. This is usually the atom with the higher effective nuclear charge. 

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