Chemical Bonding

Topics: Chemical bond, Covalent bond, Atom Pages: 9 (2928 words) Published: August 22, 2013
Chemical Bonding
Chemical compounds are formed by the joining of two or more atoms. A stable compound occurs when the total energy of the combination has lower energy than the separated atoms. The bound state implies a net attractive force between the atoms ... a chemical bond. The two extreme cases of chemical bonds are: Covalent bond: bond in which one or more pairs of electrons are shared by two atoms. Ionic bond: bond in which one or more electrons from one atom are removed and attached to another atom, resulting in positive and negative ions which attract each other. Other types of bonds include metallic bonds and hydrogen bonding. The attractive forces between molecules in a liquid can be characterized as van der Waals bonds.

What is an Ionic Bond?
An ionic bond is a type of chemical bond formed through an electrostatic attraction between two oppositely charged ions. Ionic bonds are formed due to the attraction between an atom that has lost one or more electron (known as a cation) and an atom that has gained one or more electrons (known as an anion). Usually, the cation is a metal atom and the anion is a non-metal atom. It is important to recognize that pure ionic bonding - in which one atom "steals" an electron from another - cannot exist: all ionic compounds have some degree of covalent bonding, or electron sharing. Thus, the term "ionic bond" is given to a bond in which the ionic character is greater than the covalent character - that is, a bond in which a large electronegativity difference exists between the two atoms, causing the bond to be more polar (ionic) than other forms of covalent bonding where electrons are shared more equally. Bonds with partially ionic and partially covalent character are called polar covalent bonds. Nevertheless, ionic bonding is considered to be a form of no covalent bonding. Ionic compounds conduct electricity when molten or in solution, but not as a solid. They generally have a high melting point and tend to be soluble in water. Ionic Bonding is observed because metals have few electrons in its outer-most orbital.  By losing those electrons, these metals can achieve noble-gas configuration and satisfy the octet rule. Similarly, nonmetals that have close to 8 electrons in its valence shell tend to readily accept electrons to achieve its noble gas configuration.  In ionic bonding, more than 1 electron can be donated or received to satisfy the octet rule.  The charge on the anion and cation corresponds to the number of electrons donated or recieved.  In ionic bonds, the net charge of the compound must be zero.   

This sodium molecule donates the lone electron in its valence orbital in order to achieve octet configuration.  This creates a positively charged cation due to the loss of electron.

This Chlorine molecule receives one electron to achieve its octet configuration.  This creates a negatively charged anion due to the addition of one electron. The predicted overall energy of the ionic bonding process, which includes the ionization energy of the metal and electron affinity of the non-metal, is usually positive, indicating that the reaction is endothermic and unfavorable.  However, this reaction is highly favorable because of their electrostatic attraction. At the most ideal inter-atomic distance, attraction between these particles releases enough energy to facilitate the reaction. Most ionic compounds tend to dissociate in polar solvents because they are often polar. This phenomenon is due to the opposite charges on each ions.  Examples:

 
In this example, the Sodium molecule is donating its 1 valence electron to the Chlorine molecule.  This creates a Sodium cation and a Chlorine anion.  Notice that the net charge of the compound is 0.  

In this example, the Magnesium molecule is donating both of its valence electrons to Chlorine molecules.  Each Chlorine molecule can only accept 1 electron before it can achieve its noble gas configuration; therefore, 2 molecules...
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