Chapter 10: Intermolecular Forces Flashcards
Intramolecular forces:
Forces acting within a molecule. Electrical forces between electron pairs.
Intermolecular forces:
Forces between molecules and between molecules and ions.
This what explains why atoms bond when they are not polar and the differences between melting and boiling points of substances.
What is polarity and what causes it?
Polarity is uneven charge distribution. It is caused by electron distribution.
Covalent bond:
Between non-metals and between non-metals and metalloids. This is the sharing of electrons.
What is electronegativity?
Electronegativity is when an atom wants the electrons more than another atom.
What are the Periodic Table Trends of electronegativity? And how do you determine the relative electronegativity of an atom?
Electronegativity increases left to right and decreases top to bottom. An Atoms electronegativity is determined from the Periodic Table of elements.
What are the characteristics of a Polar molecule?
When an atom is not bonded to itself–differing electronegativities, when dipoles are not in opposite directions–they do not cancel each other out, H-bond (H + N, O, F) , C=O bond (except CO2), Bent geometry (trigonal planar or tetrahedral bent) give us resulting vector, ionic species
What is an ionic bond?
A bond between a metal & non-metal when electrons are transferred
What are the characteristics of a non-polar molecule?
Atom bonds to itself, dipoles cancel ea. other out (equal in magnitude and in opposite directions), hydrocarbon, noble gases (forming diatomic molecules), diatomic molecules H2, N2, O2, Cl2, & Halogens
Why do elements in the same column behave similarly?
Because they have the same number of valence electrons.
What is an IMF and what are the different types in increasing strength?
Intermolecular force.
Dispersion, Dipole-induced dipole, Dipole-dipole, Hydrogen-bonding, and ion-dipole.
What is the relationship between kinetic energy and interactive or intermolecular forces?
When intermolecular forces are stronger the molecules have less kinetic energy.
Solid: high IMF, low KE
liquid: intermediate IMF and KE
Gas: low IMF, High
Consider: What is the velocity of the molecules?
What is the relationship between boiling point and atomic number?
When the atomic number increases so does the boiling point. There are more bonds to break.
What is the boiling point?
It is the temperature at which a liquid escapes into its gaseous form (when the pressure of the liquid equals the pressure of the environment)
What are dispersion (london) forces?
Dispersion forces are the forces that hold nonpolar atoms together. This force is created by induced dipoles.
these forces are present in ALL molecules
What is a temporary (induced) dipole?
A temporary dipole is when the nucleus of one atom is attracted to the electrons of another atom inducing a dipole. Or it is the separation of charge of an atom or molecule because of momentary uneven distribution of electrons.
What is polarizability?
It is the relative ease of an electron cloud to be distorted inducing a temporary dipole.
What are the factors that influence dispersion forces?
Size: the larger the atom/molecule the greater its polarizability and therefore the greater its dispersion force
Surface area: the larger the surface area of the molecule the greater its dispersion force ( which increases boiling point)
What is an example of dispersion?
Two atoms of same electronegativity bond together such as O2, He2 or CH4
What is the other nonpolar interaction other than dispersion?
Dipole-induced dipole. When a nonpolar molecule is polarized by the same atom in a polar molecule ie O2 interacting with the oxygen in H2O
What is the ion-dipole interaction?
IMF between an ion and a permanent dipole aka another polar molecule.
What is an example of an ion-dipole interaction?
How salt (an ion) dissolves in water: “the solubility process”
ie NaCl + H2O or MgCl2 + H2O
What is a dipole-dipole interaction?
IMF between two polar molecules
What is an example of a dipole-dipole interaction?
CH2O + CH2O, H2O + H2O
What is a hydrogen bond?
IMF between H and N/F/O
What are some examples of hydrogen bonds?
H2O + H2O and NH3 + NH3
What does solubility depend on?
IMF
What is the saying that goes with solubility and what does it mean?
“like dissolves like” a nonpolar solute is dissolved in a nonpolar solvent and a polar/ionic solute is dissolved in a polar solvent.
When can dispersion factors begin to outweigh hydrogen bonds?
Beyond five carbons in a hydrocarbon
If a molecule is nonpolar, will it dissolve in water?
No, a nonpolar molecule is not soluble in water
What does the solubility of gases in water depend on?
The temperature
The partial pressure above the liquid
The number of collisions
How does temperature affect the solubility of a gas?
The temperature: lower temp increases solubility because the molecules have less kinetic energy and are not moving around as much so as to escape the liquid
What does Henry’s law deal with and what is the equation?
Henry’s law deals with the solubility of gas.
Concentration of gas (Cgas) = Henry’s Constant (Kh) x Partial Pressure of gas (Pgas)
What can we use to find the partial pressure?
The mole fraction multiplied by the total pressure
What is vapor pressure?
Pressure exerted by gas in equilibrium with the liquid phase
What effects vapor pressure?
Temperature, surface area, and IMF
How does temperature effect vapor pressure?
Increased temperatures lead to a greater kinetic energy leading to a greater vapor pressure
How does surface area affect vapor pressure?
The greater the surface area the more molecules are in position to enter the gas phase
How does IMF effect vapor pressure?
The stronger the force the more kinetic energy needed to escape into the gaseous phase
What happens when vapor pressure reaches one atmosphere?
The vapor pressure reaches the normal boiling point and the liquid escapes to the gaseous phase.
This happens at different temperatures.
What is the association between vapor pressure and temperature?
The relationship is not linear but can be made linear through a logarithmic equation
What does the Clausius-Clapeyron equation describe? What is the equation?
The vapor pressure-temperature relationship between
ln(Pvap) = -AHvap/R (1/T) + C
y = mx + b
ln(PvapT1/PvapT2) = AHvap/R (1/T2-1/T1)
What does volatile mean? What does this mean for vapor pressure?
Volatile means that a substance readily evaporates at normal temperature and pressures. The more volatile an object the greater its vapor pressure.
What factors effect the physical state of a substance?
IMF: the strength of attractive forces compared to KE of atoms and molecules
Temperature: Increasing the temperature increases the kinetic energy of the atoms/molecules allowing them to escape into the gaseous phase
Pressure: affects the distance between atoms and molecules
What is a phase diagram and what are its aspects?
Graphical diagram that depicts how stabilities of physical states of a substance depend on temperature and pressure.
Aspects: Equilibrium lines, supercritical region, triple point, critical point, supercritical fluid.
What are the equilibrium lines of a phase diagram?
They are representative of phase changes between solid/liquid, liquid/gas, and solid/gas under specific conditions (T/P)
What is the supercritical region of a phase diagram?
It is the fourth state of matter with properties intermediate between gas and liquid.
What is the triple point of a phase diagram?
The temperature/pressure where all three phases of a substance coexist
What is the critical point of a phase diagram?
It is the specific Temperature/pressure at which the liquid and gas phases have the same density
What is the supercritical fluid of a phase diagram?
A substance above its critical temperature and pressure
What are the unique properties of water?
Water is unique because of its hydrogen bonds. Water had a neutral pH and a negative slope equilibrium line between solids and liquids designating that as pressure increases the melting point decreases: when water freezes it expands
What is the relationship between pressure and volume for most substances and how is it different for water?
For all substances when pressure increases volume decreases (Boyle’s Law) for most substances this means that volume decreases as the substance enters the solid phase. For water, volume increases as it enters the solid phase.
What is surface tension and how does it relate to IMFs?
The energy needed to separate the molecules at the surface of a liquid. As IMFs increase so does surface tension.
What is viscosity and how does it relate to IMFs?
The measure of resistance to flow of a liquid. When IMFs increase so does viscosity
What is the difference between adhesive and cohesive forces?
Adhesive: interactions between unlike particles
Cohesive: interactions between like particles
What causes a meniscus to be concave verses convex?
Concave: adhesive forces >= cohesive forces (U)
Convex: cohesive forces >= adhesive forces (upside down U)
What is the capillary action?
When a liquid rises up a narrow tube due to adhesive forces between the liquid and the tube and cohesive forces within the liquid
What factors affect viscosity?
IMF, molar mass, molecular shape, and temperature
What does a negative solid-liquid equilibrium line mean?
When the pressure is increased, the melting point decreases.
What are examples of molecules with greater IMF than water and why?
Ethylene glycol: HOCH2CH2OH
-Same 2 H-bonds as water but more bonds to break
Octane: CH3(CH2)6CH3
-No H-bonds but more than 5 central carbons
What bonds are in CH2O?
Polar bonds, NO H-bonds
