Intermolecular Forces of Attraction

Question 1

Covalent bonds are known as ___

Answer 1

Intramolecular forces

Question 2

Intermolecular forces

Answer 2

electrostatic forces of attraction which arise from the interactions of the net dipole of simple covalent molecues

Question 3

Intermolecular forces are ____

Answer 3

Weaker

Question 4

The type and strength of intermolecular forces affect the _______ of simple molecular elements

Answer 4

Physical properties (boiling point, melting point and solubility)

Question 5

Hydrogen bonding requires______

Answer 5

One molecule must contain a H atom bonded to a high electronegativity atom

The other molecule must contain an atom with a lone pair of electrons on the high electronegativity atom

Question 6

How hydrogen bonds are formed

Answer 6

N-H bond is very polar so the electron density is withdrawn from H, so H atom is left with a significant partial positive charge. The H atom will therefore experience a strong attraction from the lone pair of electrons on the other molecue, creating the hydrogen bond

Question 7

In a hydrogen bond, the H atom always faces the _____

Answer 7

Lone pair of electrons

Question 8

Hydrogen bonding is the ______ of the weak intermolecular forces

Answer 8

Strongest

Question 9

Factors affecting strength of hydrogen bonding

Answer 9

Bond polarity: The more electronegative the atom(F,O,N) that H atom is attached to, the stronger the bond

Extensiveness: More extensive, stronger (Average number of hydrogen bonds per atom)

Question 10

Properties of hydrogen bonding

Answer 10

Relatively high melting and boiling points

High surface tension （water)

Question 11

Why the boiling point of H2O is higher than that of NH3

Answer 11

Both are polar molecules with simple molecular structures.
The intermolecular force of attraction between H2O molecules and between NH3 molecules are both hydrogen bonds.
However, H2O contains 2 H atoms and 2 lone pairs on the O atom and there is an average of 2 hydrogen bonds formed per H2O molecules
On the other hand, NH3 contains 3 H atoms and 1 lone pair on the N atom and there is an average of only 1 hydrogen bond per NH3 molecule. Moreover, since O is more electronegative than N, the O-H bond will have a greater dipole moment. Thus, more energy is required to overcome the more extensive and stronger hydrogen bonds between H20 molecules compared to the weaker and less extensive hydrogen bonds of NH3 molecues

Question 12

Order of electronegativity of highly electronegative atoms

Answer 12

F>O>N,Cl