what is the difference between polar bonds and polar molecules.
i know a polar bond is a bond between two dipoles? what are polar molecules? wouldnt it be the same?
No. a polar bond is not one between two dipoles although dipole-dipole bonds do have polarity. A polar bond is one in which the electrons are completely transferred from one atom to another (an ionic bond) or a covalent bond in which the electronegativities are different resulting in one atom attracting the electrons more than the other. Two examples, one of each.
1. NaCl is an ionic compound and the bond is polar.
2. HF. The H has an electronegativity (EN) of 2.1 and the F has an EN of 4.0; therefore, the electrons of H are attracted more to F than to H so the F atom carries a slight negative charge and the H carries a slight positive charge. This is a polar covalent bond.
A polar molecule is one which satisfies the following two criteria:
a. There must be a difference in electronegativity between the central atom and at least one of the other atoms.
b. The molecule must not be symmetric in three dimensions.
Examples:
NH3 has three polar N-H bonds and it is not symmetrical in space; thus it is a polar molecule.
CCl4 has four polar C-Cl bonds but the molecule is not polar because the three dimensional space set up is symmetrical which cancels the effect of the 4 polar bonds.
what do you mean its not symmertrical in space>
Here are two examples. The NH3 molecule is a polar molecule because it is NOT symmetrical. You can see that the 3 NH bonds are pointing downward with the two unpaired electrons on top. (If the two electrons on top were replaced with another H atom, the NH4^+ ion is symmetrical.)
http://en.wikipedia.org/wiki/Ammonia
The CCl4 molecule has 4 C-Cl polar bonds because the C and Cl have different electronegativities. But see the diagram at this site. It is a symmetrical molecule in space and the molecular polarity is zero.
http://en.wikipedia.org/wiki/Carbon_tetrachloride
Great question! While polar bonds and polar molecules are related, they are not exactly the same thing.
Let's start with polar bonds. A polar bond is a type of chemical bond where there is an unequal sharing of electrons between two atoms. This happens when the electronegativity (a measure of an atom's ability to attract electrons) of the two atoms involved in the bond is different. The greater the electronegativity difference, the more polar the bond.
For example, in a molecule like HCl (hydrogen chloride), the chlorine atom has a higher electronegativity than the hydrogen atom. As a result, the chlorine atom attracts the shared electrons more strongly, creating a partial negative charge (δ-) on chlorine and a partial positive charge (δ+) on hydrogen. This separation of charges gives rise to a polar bond.
Now, let's talk about polar molecules. A polar molecule is a molecule that has a net dipole moment due to the presence of polar bonds. In other words, a polar molecule is a molecule with an uneven distribution of electron density, causing one end to be more negative and the other end to be more positive.
In addition to having polar bonds, for a molecule to be polar, it must also have a molecular geometry that does not cancel out the dipole moments of its individual bonds. This means that the overall shape of the molecule must be asymmetrical.
For example, in the water molecule (H2O), the oxygen atom is more electronegative than the hydrogen atoms. This creates two polar bonds between the oxygen atom and each hydrogen atom. Due to the bent molecular geometry of water, these polar bonds do not cancel each other out, resulting in an overall polar molecule with a net dipole moment.
In summary:
- Polar bonds are bonds between atoms with different electronegativities, resulting in an unequal sharing of electrons.
- Polar molecules are molecules that have a net dipole moment due to the presence of polar bonds and an asymmetrical molecular geometry.
So while polar bonds contribute to the polarity of a molecule, not all molecules with polar bonds are polar themselves.