Chemical Bonding

 The following list contains terms that are associated with chemical bonding.
 

Bond

 A chemical bond is a mechanism that is used to chemically combine atoms. There are three types of bonds: metallic, ionic, and covalent. In all three cases the mechanism thhat holds the bond together is an electrostatic force of attraction between areas of positive and negative charge. The locations of the areas of charge will differ from system to system. These differences are responsible for the various types of bonds generally found in substances. Bonds form as an attempt to stabilize a chemical system by releasing energy. The greater the amount of energy released during the formation of a bond, the more stable the bond will be. All bond formation processes involve the use of valence level electrons.

The bond forming process is always exothermic. If two atoms can release energy by forming a bond, then the atoms will be more stable by staying together than they would be as individual atoms. As a result, the atoms remain in the bonded condition. If two atoms gain energy in an attempt to form a bond, then the bond will NOT form. They need the benefit derived from a reduction of energy, not a gain of energy.

Conclusions,

Motivation for Bonding -- A desire to increase stability by bonding with another atom.

Mechanism for Bonding -- The electrostatic forces of attraction between areas of opposite charge.

Bond Energy

 Bond Energy is the amount of energy released when a bond forms. It is a direct measure of the amount of stability gained when two atoms establish a chemical bond. Inversely, bond energy corresponds to the amount of energy that is required to break a bond. The amount that is required to break a bond is exactly equal to the amount released when the bond formed. The magnitude of the bond energy corresponds to the vertical drop that appears in a potential energy well at the lowest point, or most stable position, in the curve. An equation that represents a bond formation process would appear as

A + B = AB + Energy.

The energy term corresponds to the energy released, or bond energy.

Bond Length
 Bond Length is the average distance between the centers of two bonded atoms. Because bonded atoms experience some vibration or harmonic oscillation, moving towards and away from each other, the distance between bonded atoms will vary slightly over a period of time. The term Bond Length specifically refers to the average positions of the two atoms during the harmonic vibrations that they undergo. On the Potential Energy Well, the Bond Length is the position on the horizontal coordinate that corresponds to the bottom of the well, or the position of lowest energy for the system.

Bond Mechanism
 The Bond Mechanism is the actual force that holds bonded atoms together. The mechanism differs from the bond motivation. The motivation explains WHY atoms would like to bond. Mechanism refers to the force that keeps them together after they have bonded. In all cases, regardless of bond type, the mechanism is an electrostatic force of attraction (Coulombic Force). The primary difference between the various types of bonds is the location of the charged areas that are responsible for establishing the electrostatic forces. For instance, in ionic systems the electrostatic force is established between the cation and the anion. In covalent types of systems, the electrostatic force is established between the positive nuclei and the negative electron cloud that exists between the nuclei.

Bond Motivation

 Bond Motivation refers to the reasons behind why bonds are established. At a very fundamental level all bonds form in order to release energy. This loss of energy, or a negative change in Enthalpy, corresponds to fulfilling one of the two driving forces. All bond formation processes are exothermic. (As a note, because bonding also involves a loss of entropy, the bond forming process will always be reversible and temperature dependent. In other words, bonds can be formed and bonds can be broken.)

At another level, the motivation is interpreted as the desire of an atom to achieve some specific type of electronic configuration that is more stable that the configuration of the unbonded atom. For instance, if an atom can duplicate a Noble Gas configuration by bonding to another atom, then that could serve as a motivation. Removal of all valence level electrons or removal of all valence level p-orbital electrons will also provide levels of increases stability. In these cases, such electronic configurations would also be a motivation for bonds being established. Ultimately, though, in all these cases, those "special" electronic configurations are more stable because of their lower energy content. In other words, motivation still returns to the idea that all atoms want to loss energy by bonding.

Bond Order

 Bond Order is the term used to distinguish between the number of bonds that exist between two atoms.

The three primary bond orders are one, two and three.

They would correspond to a single bond, double bond and triple bond.

Under some conditions, atoms may find themselves with an average bond that appears to be half-way between a single and a double. In that case, the bond order would by 1.5. Other more exotic systems may have bond orders such as 1.33. These may be a result of bonded electrons switching between positions through a process known as resonance. As a result, the average appearance of the bond over a period of time will be the bond order.



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Updated February 10, 2010