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How does electronegativity help predict whether a bond will be ionic or covalent?
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molecule
Several methods of representing a molecule's structure. In Lewis structures, element symbols represent atoms, and dots represent electrons surrounding them. A pair of shared electrons (covalent bond) may also be shown as a single dash. The ball-and-stick model better illustrates the spatial arrangement of the atoms. For aromatic compounds, the Kekulé structure is common, in which each bond is represented by a dash, carbon atoms are implied where two or more lines meet, and hydrogen atoms are usually omitted. Bond-line formulas, similar to the Kekulé structure, are often used for complex nonaromatic organic compounds. Sugars are often drawn as Fischer projections, in which the carbon “backbone” is drawn as a straight vertical line, with carbon atoms implied where horizontal lines intersect the vertical one.
Electronegativity is defined as the ability of an atom to attract a shared pair of electrons toward itself within a chemical bond. It serves as a key predictor of bond type based on the difference in electronegativity between the participating atoms:12
- Ionic Bonds: When atoms differ greatly in electronegativity, electrons are typically transferred from the less electronegative atom (typically a metal) to the more electronegative one (typically a nonmetal), resulting in the formation of ionic compounds composed of cations and anions.13
- Polar Covalent Bonds: Atoms with moderate differences in electronegativity form covalent bonds where electrons are shared unequally. This creates polarity, where the shared electrons spend more time near the more electronegative atom, resulting in partial charges.13
- Nonpolar Covalent Bonds: When atoms have approximately equal electronegativities, they share electrons more equally, resulting in little to no charge separation.1
In the periodic table, electronegativity generally increases from left to right across a period and decreases down a group.3