Chemistry- Intra and Intermolecular Forces

Question 1

intramolecular forces

Answer 1

• within the molecule

- all type of bonds (ionic, covalent, metallic)

Question 2

intermolecular forces

Answer 2

• relatively weak interactions that occur between molecules

- broken when a substance changes state

Question 3

molecular-ion attraction

Answer 3

• occurs when an ionic compound (ex. salt) is dissolved in water
• positive end of water (H) attracts the Cl- ion and negative end of water (O) attracts the Na+ ion
• results in higher boiling point

Question 4

(aq)

Answer 4

• mixture, ionic compound is dissolved in water

- shows molecule-ion attraction

Question 5

Boiling Point and IMF

Answer 5

• usually, the higher the molar mass of a compound, the greater the boiling point
• not always true for polar molecule
• the stronger intermolecular force, the higher the boiling AND melting point

Question 6

dipole-dipole attraction

Answer 6

• the positive end of one molecule is attached to the negative end of another
• molecule MUST BE POLAR (generally liquid/solid)
• strong intermolecular force
• only about 1% as strong as ionic/covalent bond

Question 7

Strength of dipole-dipole attraction

Answer 7

• decreases as distance between dipole increases

- increase in strength of dipole dipole mov’t increases the boiling/melting point and heat of fusion/vaporization

Question 8

London Dispersion (Van Der Waals) Forces

Answer 8

• occurs between NONPOLAR molecules
• temporary (induced) dipole occurs
• smaller atoms have weaker dispersion forces
• weakest intermolecular attraction

Question 9

instantaneous dipole in London Dispersion (Van Der Waals) Forces

Answer 9

• occurs accidentally in a given atom induces a similar dipole in neighboring atom
• significant in large atom/molecules
• occur in all molecules, including nonpolar

Question 10

Phase Changes

Answer 10

• due to changes in forces AMONG molecules
• solid to gas is endothermic
• gas to solid exothermic
• S to G (sublimation) and G to S (deposition)

Question 11

Density of Water

Answer 11

Gas < Solid < Liquid (exception)

Question 12

Strength of Van Der Waals Forces

Answer 12

• increases as # of electrons increase OR molecular mass increases
• decreases as distance between molecules increases (solid has highest, gas has lowest)

Question 13

Hydrogen Bonding

Answer 13

• specific type of dipole- dipole attraction
• occurs when hydrogen is bonded to N, O, or F (small atomic radius and high electronegativity)
• strongest intermolecular attraction
• strong dipole dipole forces

Question 14

Strength of hydrogen bond

Answer 14

• increases with increased electronegativity of the atom bonded to the hydrogen atom
• decrease with an increase in size of bonded atom (stronger in smaller atoms)

Question 15

Effects of Hydrogen Bond

Answer 15

• high boiling/ melting point
• low vapor pressure
• higher heat of fusion/ vaporization