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| Shared Idea |
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| Electronegativity
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| Electronegativity is a measure of an atom's ability to attract shared electrons to itself. In the periodic table, electronegativity values are generally highest in the upper right corner and lowest in the bottom left corner. Fluorine has the highest value of 4.0. The lower left has a value greater than zero, allowing for elements that have not been discovered, as of yet.
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| In 1954, Linus Pauling received the Nobel Prize in Chemistry ''for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances.'' One factor that contributed to receiving this award was his development of the electronegativity scale in 1932.
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| Electronegativity difference can help determine the type of bonding that exists between two atoms. Ions are changed particles. If an atom has gained one or more electrons, it has a negative charge and is called an anion. A group of bonded atoms that carry this trait (such as sulfate, nitrate and phosphite) are called polyatomic ions. If one or more electrons have been lost, it is a cation. Ammonium is a polyatomic cation.
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| Ionic bonds create crystals, not molecules. They consist of repeating structures of attracted ions. If the electronegativity difference is 1.7 or greater, the resulting compound is considered to be ionic. The chemical formula, such as NaCl (sodium chloride, or table salt) represents the ratio of the cations and anions. In this case, there are equal numbers of sodium ions and chloride ions, arranged in a repeating geometric pattern. If the electronegativity difference is less than 1.7, it is considered to be covalent bonding, meaning that individual chemical molecules are created, such as oxygen gas (O2), methane (CH4), water (H2O) or carbon dioxide (CO2).
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| Covalent bonds are subdivided into two further groups, referred to as polar and nonpolar. If the electronegativity difference is less than or equal to 0.5, it is classified as a nonpolar bond, such as is true for oxygen gas and methane. Molecules that have nonpolar bonds are nonpolar and do not attract one another. If the electronegativity difference is greater than 0.5 but less than 1.7, it creates a polar bond, such as in water and carbon dioxide.
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| This is where one complication occurs, however, as polar bonds can either create polar or nonpolar molecules. If the molecule is symmetrical, as in the case of carbon dioxide, it is nonpolar. The slightly positive and negative atoms are evenly distributed, resulting in molecules that are not attracted to one another. If the molecules are asymmetrical, as in the case of water, the molecules wind up being attracted to one another. The greater the electronegativity difference, the stronger the polar bonds between the molecules. In the case of water, the electronegativity difference is 1.4 and the intermolecular bonding is very strong.
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| The geometric shape of the molecules has a direct influence on determining whether the molecules are polar or nonpolar. This concept will be addressed next month.
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