about polar既問題

polar molecule is a molecule that contains a high electronegativity atom while the shape of the molecule is not symmetrical so that the bonding electrons can be drawn to the high electronegative atom such as F, Cl, O etc. Hence, it will have a net dipole moment and this molecule is called as polar.
Oppositely, if a molecule does not that has high electronegativity atom and hence it will not has a dipole moment which means the bonding electrons won't be drawn to any one of the atom, causing partial positive charge and partial negative charge.
Dipole is a molecule having a net dipole moment.
When a dipole molecule comes to a non-polar molecule, the non-polar one will be introduced to from a induced dipole.This is know as induced dipole.

Chemical polarity, also known as bond polarity or just polarity, is a concept in chemistry which describes how equally bonding electrons are shared between atoms. It is a physical property of compounds and affects other physical properties such as solubility, melting points and boiling points. Polarity also affects intermolecular forces, leading to some compounds or molecules within compounds being labelled as polar or non-polar.
Polarity refers to the dipole-dipole intermolecular forces between the slightly positively-charged end of one molecule to the negative end of another or the same molecule. Molecular polarity is dependent on the difference in electronegativity between atoms in a compound and the asymmetry of the compound's structure. For example, water is thought to be polar because of the uneven sharing of its electrons. However, methane is considered non-polar because the carbon shares the hydrogen molecules uniformally.
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. 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.
With respect to molecules there are three types of dipoles:

Permanent dipoles: These occur when two atoms in a molecule have substantially different electronegativity—one atom attracts electrons more than another becoming more negative, while the other atom becomes more positive. See dipole-dipole attractions.
Instantaneous dipoles: These occur due to chance when electrons happen to be more concentrated in one place than another in a molecule, creating a temporary dipole. See instantaneous dipole.
Induced dipoles These occur when one molecule with a permanent dipole repels another molecule's electrons, "inducing" a dipole moment in that molecule. See induced-dipole attraction.
For details, please click:
http://en.wikipedia.org/wiki/Chemical_polarity
http://en.wikipedia.org/wiki/Dipole






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