Imbalance of charge

Figure 2.6 Schematic diagram to show how an induced dipole forms when polarizable electrons move within their orbitals and cause a localized imbalance of charge (an induced dipole in which the negative electrons on one atom attract the positive nucleus on another). The dotted line represents the electrostatic dipole interaction...

A molecule is considered to be polar, or to have a molecular polarity, when the molecule has an overall imbalance of charge. That is, the molecule has a region with a partial positive charge, and a region with a partial negative charge. Surprisingly, not all molecules with polar bonds are polar molecules. For example, a carbon dioxide molecule has two polar C=0 bonds, but it is not a polar molecule. On the other hand, a water molecule has two polar O—H bonds, and it is a polar molecule. How do you predict whether or not a molecule that contains polar bonds has an overall molecular polarity To determine molecular polarity, you must consider the shape of the molecule and the bond dipoles within the molecule. 

The electroluminescence was located in the part of the anthracene crystal next to the hole-injecting anode, which suggests an imbalance of charge-carrier injection and transport. The intensity of light was linearly proportional to the... 

Imbalance of Charge Distribution in the Transition State for Car-binolamine Dehydration, J. Am. Chem. Soc., 1977, 99, 464. 

Recall from Section 2.7 that the electrons in a covalent bond are shared between the bonded atoms. In a covalent bond between identical atoms (as in H2, CI2, O2, etc.), the sharing is equal, so no imbalance of charge appears (Figure... 

In Chapter 9, you learned that a covalent bond is polar when it joins atoms of different electronegativities because the atoms share the electrons unequally. In diatomic molecules, such as HF, where there is only one bond, the bond polarity causes the molecule itself to be polar. Molecules with a net imbalance of charge have a molecular polarity. In molecules with more than two atoms, both shape ami bond polarity detennine molecular polarity. In an electric field, polar molecules become... 

Fig. 4.15. Piezoelectric property of a two-dimensional structure undeformed structure A B of symmetry p31m the resultant of the dipole moments is zero (a) the stress — a (compression) creates an imbalance of charges the resulting dipole moment per unit cell is P (b)...

On the other hand, when excess metellic ions are present in the oxide lattice of ZnO, CdO, Ti02, and AI2O3, more electrons are needed to compensate for the imbalance of charge in the oxide. These are called n-type semiconductors. 

Recall from Chapter 9 that a covalent bond is polar when the atoms have different electronegativities and, thus, share the electrons unequally, hi diatomic molecules, such as HF, the only bond is polar, so the molecule is polar. In larger molecules, both shape and bond polarity determine molecular polarity, an imbalance of charge over the whole molecule or large portion of it Polar molecules become oriented in an... 

The electrons in a molecule are in constant motion. The electron density of an He atom, for example, is spherically symmetrical on the average, but at any instant, there may be an imbalance of charge distribution in the atom. Thus, an atom or nonpolar molecule may be momentarily self-polarized because of the unbalanced charge distribu-... 

A polar bond is one in which the shared electrons are pulled more toward one atom in the bond than the other, resulting in the imbalance of charge that is a polar bond. An example is the O-H bond in a water molecule. 

Consider a situation in which a high concentration of a salt such as NaCl is added to the solution on both sides of the membrane so that the number of cations that P provides is insignificant in comparison with the number sup-phed by the additional salt. Apart from small imbalances of charge close to the membrane (which have important consequences, as we shall see in Chapter 5), electrical neutrality must be preserved in the bulk on both sides of the membrane if an anion migrates, a cation must accompany it. For simplicity, we take the volumes of the solutions on each side of the membrane to be equal. 

The imbalance of charge distribution is commonly expressed in terms of the electronegativity, X (chi), the power of an element to draw electrons to itself when it is part of a compound. Linus Pauling formulated a numerical scale of electronegativity based on considerations of bond dissociation energies, (A-B) ... 

Taking into account that relevant excitation energies are fairly constant, the paramagnetic term cXp, which represents the imbalance of charge, could be related to local symmetry. It has been established that an... 

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