Electronegativity, Intermolecular Forces Flashcards
What are dispersion forces?
Occur in individual atoms of a gas. Since the electron is not everywhere at once, there must be a slightly positive area where the electron is not present. Other electrons from others atoms are attracted to this positive charge and form a temporary dipole. This force is very weak, but strong enough to affect the volume of the gas, and is one mole of gas is less than 22.71L
- Dispersion forces are the only intermolecular forces between non polar molecules and atoms of noble gases.
- dispersion forces increase in strength with an increasing number of electrons
- the greater the flat surface area of the molecule, the stronger the dispersion force
What are dipole-dipole forces?
Weak attractive forces that occur between polar molecules, but are strong enough to affect B.P and M.P
They occur because the part of the molecule that is slightly positively charged can be attracted to the slightly negative part of another molecule. I.e in HCl, slightly negative atom Cl, may be attracted to the slightly positive H atom, from another molecule.
- present between molecules that are polar
What are hydrogen bonds?
They are extreme dipole-dipole forces. H without an electron is just a proton. A very electronegative atom such as N,O or F has a slight negative charge, and will be attracted to the slightly positively charged H. This is not an actual bond, just a very strong attractive force.
An extreme form of a dipole-dipole force
Takes place between polar molecules containing an N-H, O-H, or F-H bond and other polar molecules containing N, O or F
What happens when you put an ionic solid into a polar substance I.e water?
Example: NaCl in H2O
The slightly positive hydrogen atoms will be attracted to the slightly negative chlorine atoms, the more electronegative oxygen atoms (hence slightly negative), will be attracted to the slightly positive sodium atoms. This will separate the ionic solid into its individual ions, it dissolves into the water.
