IMF's and Phase Changes

Question 1

Coulombs Law

Answer 1

• of the charges are greater and distances similar, the greater charged compound will have more ion-ion attraction
• it will require more energy to dissociate
• greater boiling/melting pts

Question 2

Types of IMF’s (from strongest to weakest)

Answer 2

• ion bonding
• hydrogen bonding
• dipole-dipole forces
• LDF (London Dispersion Forces)

Question 3

London Dispersion Forces

Answer 3

• non-polar molecules
• instantaneous dipoles
• larger the particle, the more electrons, the more polarizable its electron cloud, the stronger the force of attraction, stronger LDF

Question 4

Dipole-Dipole Forces

Answer 4

• polar molecules
• molecules align themselves such that the opposite poles align
• result from unequal distribution of electron density (electronegativity)
• larger dipoles= stronger force of attraction=stronger dipole-dipole force

Question 5

Hydrogen Bonding Forces

Answer 5

• polar molecules in which a hydrogen atom is covalently bonded to very electronegative element (N, O, F)
• -molecules align themselves such that the opposite poles align

Question 6

surface tension

Answer 6

• surface tension of a liquid is attracted only by the molecules below and on each side of it
• increase in surface area (polar molecules)
• high surface tension= strong IMF

Question 7

capillary action

Answer 7

• spontaneous rising of a liquid in a narrow tube
• adhesive forces between molecules and glass overcome IMFS between molecules themselves
• Water= higher attraction for glass= concave
• Hg= higher attraction for other Hg molecules= convex

Question 8

viscosity

Answer 8

• resistance to flow

- molecules with larger IMF’s and more complexity have more resistance

Question 9

vapor pressure

Answer 9

• pressure resulting form the particles of a substance that exist in the vapor phase above the liquid in a close container
• weaker IMF= higher VP bc the substance will more easily overcome the forces and break away to vapor phase
• increase temp= increase VP

Question 10

Boiling point

Answer 10

• temperature at which the VP of a liquid equals the atmospheric pressure
• all molecules have enough energy to overcome IMF
• normal BP= temp at which the VP of a liquid equals 1 atm

Question 11

molecular solids

Answer 11

• molecules with LDF, D-D, or Hydrogen bonding
• contains arrangements of atoms or molecules that are organized in an orderly 3D pattern
• soft; Low melting points

Question 12

ionic solids

Answer 12

• consists of cations and anions distributed throughout in an ordery 3D pattern - crystal lattice
• cations positioned in holes between anions
• hard, brittle
• high melting points, which are a result of the electrostatic attractions of the ionic bonds (stronger than IMF in molecular solids)

Question 13

covalent network solids

Answer 13

• atoms held together in large networks containing extended covalent bonds
• ex: carbon in the form of graphite or diamond

Question 14

atomic solids

Answer 14

• individual atoms held together by weak LDF’s
• low MP
• noble gases

Question 15

metallic solids

Answer 15

• metallic atom’s nuclei surrounded by freely moving electrons
• band theory= states that the atomic orbitals of these atoms mix to form a range of molecular orbitals that encompass all energy levels
• empty orbitals= electrons move freely from orbital to orbital
• good conductors of electricity and heat
• shiny
• high melting points

Question 16

phase diagrams

Answer 16

-graphically represent the relationship of the 3 states of a pure substance in terms of pressure and temperature

Question 17

neg slope on water’s phase diagram means……

Answer 17

-solid is less dense than liquid

Question 18

heating and cooling curves

Answer 18

• graphically represent the relationship of a pure substance in terms of how the temperature changes over time
• q=mcΔT
• q=ΔH

Question 19

polar solvent and polar solute

Answer 19

• large ΔH to overcome large IMF
• strong IMF’s between solute-solute and solvent-solvent must be overcome–> significant imput of energy
• solute and solvent form strong interactions between each other, releasing an equal amount of energy
• solute dissolves bc it gets as much energy back form interactions as was required to overcome IMF

Question 20

non-polar solvent and non-polar solute

Answer 20

• small ΔH to overcome weak IMF
• weak IMF’s between solute-solute and solvent-solvent must be overcome
• solute and solvent form weak interactions between each other, releasing an equal amount of energy

Question 21

non-polar solvent and polar solute

Answer 21

• IMF in polar solute is large but ΔH required for non-polar solvent is small
• interactions are small/weak
• solute cannot dissolve