Consider two charges A(+) and B(-).Let the charges be represented by Q and -Q respectively.Let the distance between them be d.Polarity is nothing but Q*d(in simple terms of course. Polarity of bonds:- Electrons are not always shared equally between two bonding atoms; one atom might exert more of a force on the electron cloud than the other. In which case can make a dipole-dipole intermolecular force. This pull is termed electronegativity and measures the attraction for electrons a particular atom has. The unequal sharing of electrons within a bond leads to the formation of an electric dipole: a separation of positive and negative electric charge. Partial charges are denoted as δ+ (delta plus) and δ− (delta minus). These symbols were introduced by Christopher Ingold and his wife Hilda Usherwood in 1926. Atoms with high electronegativities — such as fluorine, oxygen, and nitrogen — exert a greater pull on electrons than atoms with lower electronegativities. In a bond, this can lead to unequal sharing of electrons between the atoms, as electrons will be drawn closer to the atom with the higher electronegativity. Bonds can fall between one of two extremes — being completely nonpolar or completely polar. A completely nonpolar bond occurs when the electronegativities are identical and therefore possess a difference of zero. A completely polar bond is more correctly called an ionic bond and occurs when the difference between electronegativities is large enough that one atom actually takes an electron from the other. The terms polar and nonpolar are usually applied to covalent bonds, that is, bonds where the polarity is not complete. To determine the polarity of a covalent bond using numerical means, the difference between the electronegativity of the atoms is taken. On the Pauling scale, if the result is less than 0.4, the bond is generally nonpolar covalent. If the result is between 0.4 and 1.7, the bond is generally polar covalent. If the result is greater than 1.7 the bond is generally considered ionic. Pauling considered that the partial ionic character of a bond is an approximate function of the difference in electronegativity between the two bonded atoms. He estimated that a difference of 1.7 corresponds to 50% ionic character, so that a greater difference corresponds to a bond which is predominantly ionic.
Posted on: Sat, 15 Nov 2014 04:03:54 +0000
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