Chemistry AS ES CI 5.3 and 3.1
- Created by: A.B.
- Created on: 19-02-14 11:01
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- ES Bonds between molecules: temporary and permanent dipoles CI 5.3 and 3.1
- Polar Molecules
- A dipole occurs when a molecule (or part of a molecule) has a positive end and a negative end. When a molecule has a dipole, we say it is polarised. Molecules with a permanent dipole are polar molecules.
- Instantaneous (temporary) dipoles
- The electron density in a molecule may be unevenly distributed at any one time (if no permanent dipole)
- The electron density distribution changes and so the polarity will change
- If other molecules are close to a molecule with a dipole these may cause an effect and produce an induced dipole.
- The electron density in a molecule may be unevenly distributed at any one time (if no permanent dipole)
- Intermolecular bonds
- Molecular substances which contain dipoles attract each other. Two of these kinds of attraction are instantaneous dipole-induced dipole bonds and permanent dipole-permanent dipole bonds.
- Instantaneous dipole - Induced dipole
- very weak
- can happen even if permanent dipole already
- Permanent dipole - permanent dipole bonds
- stronger than ID-ID but weaker than hydrogen bonds
- Electronegativity
- The degree to which an atom of an element attracts electrons is called its electronegativity. The more electronegative an element an element is than the greater its attraction for electrons
- The order of electronegativity values for some common elements is
- F > O > Cl > Br
- N > I > S > C > H
- Difference between C and H is so small that molecules are said to be non polar
- The order of electronegativity values for some common elements is
- The degree to which an atom of an element attracts electrons is called its electronegativity. The more electronegative an element an element is than the greater its attraction for electrons
- Bond polarity and polar molecules
- A polar molecule is one that has a permanent dipole
- Some molecules with a polar bond may not be a dipole if the bonds have a symmetrical arrangement
- Polar Molecules
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