Polarisation and Intermolecular Forces Flashcards
Explain the trends in electronegativity.
Across and up the period electronegativity increases.
What is electronegativity?
The ability to attract bonding electrons in a covalent bond.
What is a dipole?
The difference in electronegativity between atoms caused by a shift in electron density.
Name the three intermolecular forces.
Van der waals, permanent dipole dipole and hydrogen bonding
Explain how Van der Waals forces work.
The electron in the charge cloud are to one side of the positively charged nucleus. This is a temporary dipole which induces another temporary dipole.
How can different van der waals forces be of different strength?
Larger molecules have larger electron clouds, meaning strong van der waals forces.
How does surface area affect van der waals forces?
It makes the forces strong as they have a greater exposed electron cloud.
Explain permanent dipole forces.
The slight positive and negative charges in polar molecules cause weak electrostatic forces of attraction between molecules.
Hydrogen bonds occur when hydrogen is covalently bonded to specific elements, what are these elements?
Nitrogen, oxygen and fluorine.
Why does hydrogen have a high charge density?
It’s so small.
Why do hydrogen bonds occur?
As hydrogen has such a high charge density and O, N and F are so electronegative. The bond is extremely polar that weak bonds form between hydrogen of one molecule and the N, O, or F of another molecule.
How do hydrogen bonds effect the physical properties of substances?
Have higher freezing and boiling points relative to non polar molecules of that size.
Why is ice less dense than water?
Hydrogen bonds are relatively longer than water one and ice has more hydrogen bonds.
