Water: Noncovalent Interactions

Question 1

What are the three types of Van der Waals?

Answer 1

Question 2

Define dipole.

Answer 2

Neutral molecules were the center of gravity of the negative charge does not coincide with the center of gravity of the positive.

Question 3

What is the “van der waals envelope”?

Answer 3

“ surface of the molecule”

Question 4

Do atoms from different molecules come closer together than the sum of their van der waals radii?

Answer 4

Very rarely EXCEPT for the “hydrogen bond”

Question 5

What is notable about water? The Å length of the O-H bond?

Answer 5

1. Nonlinear molecule
2. Carries permanent dipole moment
3. Bond about 1 Å long.

Question 6

10 Å = x nm = y m

Answer 6

x=1
y=10^-9

Question 7

What is the length of the covalent O-H bond and the H-bond’s respectively? Bonus: O-O interaction?

Answer 7

Question 8

As ice, how many H-bonds does water make?

Answer 8

4 H bonds.

Question 9

As liquid, how many H-Bonds does water make?

Answer 9

<4 H Bonds. (To much rapid movement to have 4, like ice)

Question 10

Why is water so crucial for life on earth?(2)

Answer 10

1. Water as ice becomes less dense than liquid (more open lattice formation of H-bonds). Making ice float to the top and act as an insulator for early life forms.
2. Because of so many H-bonds, water has a very high boiling point for how small a molecule it is, allowing it to stay liquid when most other same sized molecules are gas.

Question 11

What are the H-Bond donors and acceptors of this picture? What elements are acceptors in this class? What about donors?

Answer 11

Donors : O-H, N-H. Acceptors: O, N

Question 12

What is a hydration shell?

Answer 12

When the permanent dipoles of water molecules interact very favorably with charged ions and solution.
Note: NOT ALL SALTS DISSOLVE READILY IN WATER