Polar substances are covalently bonded substances that contain partially positive and negative charges. The partial charges within a polar substance are a result of electronegativity differences between the atoms that share the covalent bond. Electronegativity is the likelihood that an atom will attract a pair of bonded electrons. The greater the electronegativity, the greater the attraction that an atom has for a pair of bonded electrons. The range of electronegativity differences is approximately 0.7 to 4.0. Some periodic tables contain electronegativity values of for each element. The electronegativity difference between two atoms forming a bond can be used to determine the type of bond that will be formed between the two atoms, as identified below.
- Electronegativity differences less than 0.5 = nonpolar covalent
- Electronegativity of 0.5 – 1.6 = polar covalent
- Electronegativity difference of 2.0 or more = ionic bond
(However, if the electronegativity difference between to atoms falls between 0.5 and 1.6, but there is symmetry within the compound, then that compound will not display polarity. This is the reason why carbon dioxide (CO2) is not considered to be polar.)
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