U3 - Module 1: Analyzing Molecular Structure Flashcards
Hydrophilic Molecules
Tend to be more polar and have stronger IMFS from attracting water.
Hydrophobic
Tend to be non polar and have weak molecular interactions from repelling water.
What do physical properties of molecules arise from?
The collective IMFs in the molecule
What 3 things affect how a molecule interacts with other particles?
- Molecular geometry
- Bond polarity
- Molecular polarity
What is the relation between IMFs and states of matter?
IMFs will keep molecules together in the lower state of matter.
- Molecules need to gain enough kinetic energy to move to a higher state of matter.
What does having stronger IMFs mean?
- There are strong intermolecular attractions (harder to break)
- Requires more energy to break bonds
What are the 3 examples of having strong IMFs?
- Higher boiling/melting points
- Lower vapor pressure and lower volatility
- Higher viscosity
Why do stronger IMFs cause higher boiling/melting points?
Requires more energy to bring molecules to the higher state of matter.
Why do stronger IMFs cause lower vapor pressures/voltality?
Since the attractions between atoms are stronger, it is harder for molecules to move from the liquid to gas state
= lower evaporation levels
Why do stronger IMFs cause higher viscosity?
Stronger bonds between atoms makes it harder for substance to flow out.
Viscosity
How easily a liquid flows
How do highly viscous substances act?
Flow very slowly
What is the relationship between atomic size, ionization energy, and electronegativity?
As size increases…
- Ionization energy and electronegativity levels decreases
Ionization Energy
The amount of energy needed to remove an electron from the atom.
Explain why as size increases, ionization energy decreass?
As size increases electrons become more distanced from the nucleus, losing the attractive forces the further apart they move.
Since the attractive levels are lower, less energy is required to remove an electron from the atom.
What can nonmetallic elements combine to form?
Polar covalent bonds
What is the formula for EN difference between atoms?
EN = | ENa - ENb | < 2
What does this formula mean:
EN = | ENa - ENb | < 2
Any elements that have an EN difference lower than 2 are found to be nonmetal bonds (covalent).
How are many physical properties of molecular compounds determined?
By the strength of the interactions between their molecules.
What can polarity be considered?
A differentiating characteristic
What are the 3 differentiating characteristics that can be responsible for differing molecular properties?
- Size/shape/geometry
- Bond and molecular polarity
- Mass and total # of electrons
How do intermolecular forces arise?
The charged regions of molecules that attract or repel each other with forces that vary depending on the intermolecular distance.
What 3 things are the strength of IMFs dependent on?
- Bond polarity
- Molecular polarity
- Polarizability
Bond Dipole
The measure of uneven distribution of valence electrons in a BOND.
Molecular Dipole
The measure of uneven distribution of valence electrons in a MOLECULE
Polarizability
The measure of how electrons in an atom, molecule, or ion are affected by the presence of other atoms, molecules, or ions nearby.
Explain the 2 outcomes of polarizability.
- The presence of a negative atom causes the electron cloud to repel away from the atom.
- The presence of a positive atom causes the electron cloud to attract to the atom.
What happens to the EN when polarizability occurs?
Makes one side g+ and the other g- (dipole moment)
Induced Dipole Moment
A dipole moment can be created or strengthened due to the presence of a charged atom being put near a molecule (polarizability)
When two atoms have the same number of electrons but differing sizes, which would be more polarizable?
The larger atom
Electrons are more spread out and easier to move around (less attractive forces to nucleus)
When two atoms have the same size but different number of electrons, which would be more polarizable?
The atom with more electrons
There is a higher chance for electrons to react with the charge of the nearby atom.
When two atoms have different sizes and different number of electrons, which would be more polarizable?
The larger atom
Size plays a larger role than amount of electrons.
Are gases or solids more electronegative?
Gases
What two factors increase polarizability?
- More electrons
- Larger size
Dispersion Forces
When two molecules/atoms get close together, the IMF interactions between electrons and protons induce a temporary dipole moment.
What happens when a temporary dipole moment is induced?
Particles from different atoms/molecules attract each other.
What is the major contribution to intermolecular forces?
Dispersion forces
What molecules have dispersion forces?
ALL MOLECULES
What indicates a dispersion force in an image?
Dashed lines = temporary interaction
When an atom and a compound have around the same electrons and mass, which has an assumed higher boiling point?
The compound
What is the relationship between dispersion forces and polarizability?
The relative strength of dispersion forces increases as the polarizability of molecules increases.
What is the relationship between polarizability and vapor pressure/volatile?
The more polarizable something is, the lower vapor pressure it has and is less volatile.
When are dipoles stronger?
When it is easier to create induced dipoles
Why do larger molecules have stronger IMFs?
There are more contact areas where polarization/dispersion forces can occur.
What is the difference between molecules with flat geometries and molecules with spheric geometries?
Molecules with flat geometries have stronger dispersion forces and are more polarizable because they have more surface area where dispersion interactions can occur.
Do phenyls have strong or weak dispersion forces?
Strong - flat geometry
What role does molecular polarity play in IMFs?
When dipoles are present in a molecule, it increases the polarizability and strength of IMFs.
Explain the case of molecular polarity when a molecule is polar.
Contributions to IMFs arise from the presence of permanent molecular dipole moments in the system.
Dipole Dipole Forces
Additional permanent attractive contribution to the total IMFs between polar molecules.
What is the total IMFs in POLAR MOLECULES composed of?
Dispersion forces and dipole-dipole forces
Electrostatic Potential Map
A 3D representation of charge distribution in a molecule used to show regions of positive and negative electrostatic potential
What do electrostatic potential maps help predict?
How molecules interact with each other.
What do dispersion and dipole dipole forces make up?
The total IMFs of polar molecules
Just because a molecules has more types of IMFs means they have higher boiling points.
NO
What IMF is related to polarizability?
Dispersion
What IMF is related to molecular polarity?
Dipole-Dipole
What do polar molecules have?
Dipole-dipole interactions
What IMF is related to bond polarity?
Hydrogen Bonding
When is bond polarity relavent?
When H is bonded to N, O, or F
Why are hydrogen bonds so strong?
N, O, and F are the most EN molecules, and small in size so bonds can come very close together.
Hydrogen bonding behavior vs hydrogen bond
Hydrogen bonding behavior: Hydrogen has a H-O, H-n, or H-F bond that can create a hydrogen bond in another molecule
Hydrogen bond: Two molecules interact and create a bond with hydrogen and two other atoms (O,N,F)
How do you draw a molecular structure when hydrogen bonding is present?
Draw dashed lines to show the hydrogen bonds.
What 3 factors do you examine for dispersion bonds?
- Number of electrons
- Size
- Shape
Wha factor do you examine for dipole-dipole bonding?
The net dipole moment
What 2 factors do you examine for hydrogen bonding?
- Strength
- Hydrogen bonds present
Compare the energy needed to overcome IMFs and the energy to break a covalent bond?
The energy needed to overcome IMFs is smaller than those needed to break a covalent bond
What is the order of IMFs based on most common to least common?
- Dispersion
- Dipole-Dipole
- Hydrogen Bonding
What is the order of IMFs based on strength, strongest to weakest.
- Hydrogen bonding
- Dipole-Dipole
- Dispersion
What is the relative strength of different types of IMFs dependent on?
The type of molecule
Liquid Alkanes
Lubricants (oils)
What characteristics do liquid alkanes have?
- High viscosities
- Low volatiles
= HIGH IMFs
Structural Isomers
Molecules that have that same molecular formula, weight, and number of electrons…
But have different structures
How do you determine which structural isomer will have the highest polariazability?
The one with the flattest structure
- Can easily get close with other molecules on a larger surface area.
What do more tightly structured molecules have that flat molecules do not?
Branches
What does the presence of branching do?
Reduces the effective contact area of the molecules that can interact, decreasing IMFs
What 4 characteristics do lower IMFs lead to?
- Low melting points
- Low boiling points
- Low Viscosities
- HIGH VOLAlITIES (vapor pressure)
What are characteristics of ideal gases?
- Small masses
- Weak IMFs
What type of molecule is the least polar in water?
Nonpolar
INTRAmolecular forces
Forces that hold atoms together inside a molecule
INTERmolecular focres
Forces that hold different molecules together
What two factors is the miscibility of substances dependent on?
- Strength of IMFs
- # of configurations
What IMF strength is needed for substances to mix?
STRONG IMFs to hold the molecules together when they mix
What # of configurations is needed for substances to mix?
HIGH number of configurations
What is the relationship between IMFs and potential energy level?
Strong IMFs are correlated to low potential energy levels
Why are more configurations a better factor for substances to mix?
The more configurations a mixture has, the more options for equal molecular arrangements with preferred IMF interactions
What molecules is higher number of configurations more common in?
Molecules with
- Similar size
- Similar structure
- Similar PE levels
What are the y and x axis on the PEC diagrams for mixing substances?
Y - Potential energy increasing UP
X- # of configurations increasing to the RIGHT
What would a PEC diagram of two substances that always mix look like?
The UM substance would have lower configurations, and higher potential energy (upper left)
The M substance would have higher configurations and lower potential energy (lower right)
= meets ideal conditions of miscosity
What would a PEC diagram of two substances that never mix look like?
The UM substance would have higher configurations and lower potential energy (lower right)
The M substances would have lower number of configurations and higher potential energy (upper left)
= meets none of the ideal conditions of miscosity
What would a PEC diagram of two substances that slightly mix at higher temperatures look like?
The UM substance would have lower configurations and low potential energy (lower left)
The M substance would have higher configurations and higher potential energy (upper right)
- Higher potential energy distinguishes higher temperature
= Only 1 condition met
How would you draw the arrow between the two substances on the PEC diagram?
The arrow goes from the UM substance to the M substance
How do types of IMFs impact substances ability to mix with each other?
Molecules that have the same IMFs will mix with each other
- “like dissolves like”
What does “Like dissolves like” mean?
Polar molecules will mix with polar molecules
Nonpolar molecules will mix with nonpolar molecules
Endothermic
Energy is taken in (>0)
Exothermic
Energy is released (<0)
What would the PEC diagram look like if a mixture is endothermic?
The potential energy of UM would be lower than the PE of M
What would the PEC diagram look like if a mixture is exothermic?
The potential energy of UM would be higher than the PE of M
Does raising temperature affect the miscibility of an endothermic or exothermic mixture?
Endothermic
Does lowering temperature affect the miscibility of an endothermic or exothermic mixture?
Exothermic
Miscibility
The ability for two substances to mix into an equal/homogenous solution.
Conditional Solutions
Only 1 of the two conditions for miscibility is met, leaving the ability to alter the environment to increase the chance of the two substances to mix together.
Is a higher or lower potential energy level more stable?
Lower level
What would the PEC diagram look like for a mixture that always mixes but does not change with temperature?
The UM would have lower configurations (left) and the M would have higher configurations (right)
The PE level for both states would be the same
What would the PEC diagram look like for a mixture that NEVER mixes but does not change with temperature?
The UM would have higher configurations (right) and the M would have lower configurations (left)
The PE level for both states would be the same
If one substance is polar, and the other is nonpolar, will they mix?
No - Not the same kinds of molecules
When the M and UM states have the same PE level, what is the relationship of temperature and solubility?
The solubility is independent of temperature since they have the same PE (temp)
What is the relationship between physical properties of compounds and intermolecular interactions?
They influence each other
Why do intermolecular forces arise in molecules?
Atoms, molecules, and ions have charged regions in a particle that can be unevenly distributed and changing.
What is the relationship between strength of IMFs and strength to remove those forces?
The stronger the IMFs - The more energy is needed to separate the molecules from each other.
What 3 factors determine physical properties of molecular compounds?
- Polarity of molecules
- Polarizability of molecules
- Possibility of hydrogen bonding
Induced Dipole Induced Dipole
Type of dispersion force
- Weak attractions that occur when temporary changes in electron density in one nonpolar molecule, induces a similar shift in a nearby molecule.
Dipole Induced Dipole
When a nonpolar substance interacts with a polar compound.
