Intermolecular Forces Information Page
Broad definition of what we are considering
We are considering electrostatic attractive forces BETWEEN species. This generally means between two separate molecules or between two separate parts of a molecule but could be between a molecule and an ion. This includes how these interactions are formed as well as how the relative charges/partial charges on the species and the distance between species affect the strength of the electrostatic attraction (Coulomb’s law).
To meet the concept of interest: Video must either describe HOW IMFs are formed OR explicitly connect physical properties of substances to TYPES and RELATIVE STRENGTHS of IMFs.
Videos designed to just answer a very narrow question (e.g., which substance would have a bp closest to that of Ar?) are not ones we will do a full evaluation of.
Videos where IMFS are mentioned and explained but the focus is not IMFs, e.g.,a video focused on the physical properties of water are not ones we are going to evaluate.
Johnstone's Triangle Elements
Gas Law Specific Criteria
| Element | Examples |
|---|---|
| Macroscopic |
Visible phenomena - differences in physical properties of substances: molecular
compounds in different phases at Room temp - sugar vs hexane; differences in mp or bp
- water vs. ethane; differences in viscosity - water vs. glycerol; for BP, specific
examples and values are often expected if only briefly addressed. |
| Symbolic |
Chemical formulas of substances; Potential energy well diagram; graphical
representation of relative strength of forces; Coulomb’s Law; using arrows to show
dipole moments; Dashed lines between molecules representing IMFs; Lewis structures
of molecules - showing three or more LS interacting counts as particulate. |
| Particulate | Particle representations of molecules oriented appropriately for electrostatic interactions OR that illustrates something like increase surface contact (for LDFs); Bohr or QM type model showing unequal distribution of electrons. Showing unequal distribution of electrons in atoms for LDFs is included in particulate. |
| Connection between levels |
Videos should make explicit connections between two or more levels for this to be
coded as present. For example, they could show a macroscopic example of things that
are miscible or immiscible and then show the particle interactions between the miscible
and immiscible components. |
Core Ideas
| Core Ideas Elements | ||
|---|---|---|
| Electrostatic Bonding and Interactions | Energy | Atomic/Molecular Structure & Properties |
| Attractive and repulsive electrostatic forces govern noncovalent and bonding (covalent and ionic) interactions between atoms and molecules. The strength of these forces depends on the magnitude of the charges involved and the distances between them. | Kinetic and potential energy changes occur when atoms and molecules interact. Energy is released to the surroundings when attractive noncovalent interactions form, and conversely, energy is required to overcome noncovalent interactions. | The macroscopic physical and chemical properties of a substance are determined by the three‐dimensional structure, the distribution of electron density, and the nature and extent of noncovalent interactions between the particles. |
|
Video needs to include: Intermolecular forces (attractive noncovalent interactions) exist between atoms/molecules due to instantaneous, induced, and permanent dipoles. AND The strength of the attraction depends on the size of the dipole. (Needs to have this last part!) Difference between this and CMR Option 1 is that for CMR video must include HOW the dipoles (permanent or temporary) are formed. |
Video is likely to include: Energy is required to overcome intermolecular attractions between molecules to change phase from solid to liquid to gas, and conversely, energy is released to surroundings when molecular compounds change phase from gas to liquid to solid. Discussion of phase changes is not required though. |
Video needs to include: Physical properties of molecular compounds can be explained based on the type(s) and strength(s) of IMFs that exist between particles. AND Describe how a change to the strength of the IMF will influence the physical property (e.g., as IMF strength increases, boiling point will increase). |
Casual Mechanistic Reasoning
Option 1: What governs the strength of attraction between molecules (IMFs)?
How:
- Molecules are attracted to each other based on the partial charges (temporary or permanent) that exist. Opposite charges attract. The strength of attraction depends on the size of the dipoles (e.g., LDFs tend to be weaker than D-D as instantaneous dipoles are weaker than permanent dipoles).
Why:
- Particles develop partial charges based on the distribution of electrons within a molecule. Unequal sharing or complete transfer of electrons leads to permanent charges (partial or full charges respectively). Temporary dipoles are formed due to an asymmetric distribution of
electrons within an atom or molecule (either through random motion or in response to another atom/molecule/ion/or electrical field). This should be addressed for each IMF type presented.
Must have both parts! For videos that just talk about one type of IMF (e.g., DD) just need to describe why for the relevant IMF type.
Option 2: What drives the formation of attractions between molecules (IMFs)?
How:
- The strength of IMFs is governed by the magnitude of the charges involved and the distance between the interacting species.
Why:
- The formation of attractive forces between species results in a lower potential energy state for the system and a corresponding release of energy to the surroundings, or conversely overcoming attractive forces requires energy. Stronger attractions release more energy when formed/require
more energy to overcome.
Must have both parts!
Option 3: What is the relationship between different types of IMF’s and physical properties?
How:
- Physical properties depend on the strength of attractive forces between individual particles in the substance.
Why:
- Mp/bp will increase with increasing strength of IMFs, because more energy is required to overcome them.
- Viscosity will increase with increasing strength of IMFs, because more energy is required to allow the molecules to move past each other.
- Vapor pressure will decrease with increasing strength of IMFs, because less energy will be required to overcome them and get into the vapor phase.
Does not need to explain all of these but generally needs to explain some well.
Must have both parts!
Scientific Practices
| Most Frequent Science Practices |
|---|
SP 2: Developing and Using Models
|
SP 4: Analyzing and Interpreting Data
|
SP 6: Constructing Explanations and Engaging in Argument from Evidence
|
Multimedia Principles
Multimedia learning as knowledge construction: The goal of multimedia presentations is not only to present information but also to provide guidance for how to process the presented information – that is, for determining what to pay attention to, how to mentally organize it, and how to relate it to prior knowledge. We will categorize the videos along each of the following criteria (High and Low should be mutually exclusive.)
| High | Low |
|---|---|
|
|
Misleading vs. Inaccuracies
Analogies
Compares dipole interactions to magnets. Shows magnet attraction and repulsion on camera.
Misleading
- Says that water molecules have strong bonds between them. Instructor says that Hydrogen Bonds are a type of bond, not an IMF. Says that breaking these “bonds” requires a lot of energy.
- Various personifications of molecules. Atoms are drawn as cartoon people. Charged attraction is sexual attraction, Electron affinity and IMF strength is physical strength.
- Several minor spelling issues is misleading, not inaccurate
- Note: common confusing issue
- Some videos use the terms van der Waals forces and London dispersion forces
interchangeably. - Official IUPAC definition for van der Waals forces: The attractive or repulsive
forces between molecular entities (or between groups within the same molecular
entity) other than those due to bond formation or to the electrostatic interaction of
ions or of ionic groups with one another or with neutral molecules. The term
includes: dipole–dipole, dipole-induced dipole and London (instantaneous
induced dipole-induced dipole) forces. The term is sometimes used loosely for the
totality of nonspecific attractive or repulsive intermolecular forces.- Source: PAC, 1994, 66, 1077. (Glossary of terms used in physical organic
chemistry (IUPAC Recommendations 1994)) on page 1175 [Terms]
[Paper]
(https://goldbook.iupac.org/terms/view/V06597#:~:text=https%3A%2F%
2Fdoi.org%2F10.1351,bond)
- Source: PAC, 1994, 66, 1077. (Glossary of terms used in physical organic
- Some videos use the terms van der Waals forces and London dispersion forces
Example High Quality Videos
Examplar Videos
These are examples of videos that were found to provide good illustrations of some or many of the framework components for this concept. Develop a deep understanding of chemistry concepts requires multiple experiences with the material and these videos may provide one such experience.
|
Exemplar Video 1 |
Exemplar Video 2 |
|
Strengths Provides very good segmenting through flow chart at beginning and end. Provides an animation and explanation of how induced dipole forms and gives many examples of how different atoms have more/less LDF which leads to macroscopic properties like protein folding and boiling point. |
Strengths Good overview on all the types of interactions and shows the particles oriented correctly. Connects concept of electronegativity and dipoles and the relative strength of charge to strength of IMF attraction. Clearly articulates hydrogen bonding is dipole and all atoms have LDF. Shows example vector analysis. |
|
Weakness Instructor on screen, only covers LDF. |
Weakness Instructor on screen, says energy is stored in bonds and does not clearly state energy is used to overcome IMF/electrostatic attraction, but to overcome energy stored in bonds. Honestly, 0:00-5:20 is really good. Second half is good but kinda drags on. |
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