Intramolecular bonding is the name given to the
chemical bonds inside molecules. All intramolecular bonds are strong. The following are some examples:
- A pure covalent bond is a pair of electrons equally shared between atoms.
- A polar covalent bond is a pair of electrons unequally shared between atoms.
- A dative covalent bond is a covalent bond where both electrons come from the same atom.
- Van der Waals forces
- Dipole-dipole
- Hydrogen bonding
1.
Van der Waals forces
Out
of the three, this is the weakest
intermolecular force. They form between
temporary dipoles in one molecule and induced dipoles in another. They are constantly
changing and the strength of attraction depends on the number of electrons in
the molecule.
The shape of the molecule is also
important:
A large surface area = more Van der Waals
forces = strong attraction.
Below is showing Van der Waals
forces occurring between 2 molecules of hydrogen:
The particle on the left has
formed a temporary dipole maybe caused by one side of it being more dense than
the other. For a brief moment one end of the particle has a positive charge and
the other end with a negative charge, causing a nearby particle to also have a
temporary dipole.
2.
Dipole-dipole
These forces are stronger than
Van der Waals and occur between polar
molecules meaning that they have permanent
dipoles.
Remember! The greater the difference
in electronegativity the bigger the dipole and the stronger the attraction is
between the molecules (refer back to my previous blog
The diagram below is showing the
dipole-dipole attraction between two HCl molecules. The negative dipole on the
chlorine atom is attracted to the positive dipole of another HCl molecule:
3. Hydrogen bonding
This is the strongest
intermolecular force but it only occurs between molecules in which hydrogen is
bonded to nitrogen, oxygen or fluorine.
Hydrogen
bonding is the attraction between an
electron deficient atom on one molecule and a lone pair of electrons on a
highly electronegative atom on a different molecule.
The
diagram above shows hydrogen bonding in water. The positive dipole on the hydrogen
atom is attracted to the lone pair of electrons on the oxygen atom in another
water molecule.