Unit 8: intermolecular forces

Question 1

What are intra-molecular forces?

Answer 1

• Interactions of atoms within a molecule
• Can be metallic, ionic or covalent
• Stronger than intermolecular forces

Question 2

What are inter-molecular forces?

Answer 2

• Interactions between molecules, atoms or ions, so between chemical species
• Affect physical propreties, such as boiling and melting point
• State of matter depends on the magnitude of intermolecular forces (Liquids and solids = strong and gases = weak)

Question 3

What are metallic bondings?

Answer 3

• Between metallic atoms
• Valence electrons move freely through the structure

Question 4

London dispersion force (LDF)?

Answer 4

• Type of inter-molecular force (temporarily)
• All substances have LDF
• When electrons are temporarily unsymmetrically distributed in a molecule
• Results in short-lived dipole moments, that creates polarity in molecules, even in non-polar bonds
• Larger atoms/molecules are said to be polarized, because have more electrons
• Consequences: higher melting and boiling points that expected

Question 5

Dipole-dipole interactions?

Answer 5

• Type of inter-molecular force (permanent)
• Between polar molecules with net dipoles
• Permanent dipole due to uneven sharing of electrons
• Consequences: higher melting/boiling points than nonpolar molecules

Question 6

Hydrogen bonds?

Answer 6

• Strong dipole-dipole interaction
• O-H, N-H, F-H bonds are highly polarized
• Due to very small size of hydrogen atoms

Question 7

Ion-dipole forces?

Answer 7

• Electrostatic attractions between ions and polar molecules
• Ex: NaCl in water
• Most commonly found in solutions
• The strongest force