IB Chemistry IA idea · Structure, bonding and data
IB Chemistry IA idea: can a computer predict molecular polarity?
Dipole moments depend on bond polarity and shape; calculate them and test against measured values.
These ideas are starting points, not an IA to copy. Never copy an idea blindly: make the question, method and analysis your own, and check your plan with your teacher.
Example research question
How closely do dipole moments (D) calculated for CH₄, CH₃F, CH₂F₂, CHF₃, CF₄ and CH₃Cl in a free modelling program match the experimental values in the NIST CCCBDB?
Change the system, the range or the method so the question is yours. Check it against the research question checklist in our Chemistry IA guide.
Variables
- You change
- Molecule (a series where polarity changes, such as CH4, CH3F, CH2F2, CHF3, CF4), 6 or more
- You measure
- Calculated dipole moment (debye), and its difference from the experimental value
- You keep the same
- Same software, method and basis set
- Geometry optimisation settings
- Same experimental source (CCCBDB)
Method
Model each molecule in a free package, optimise the geometry, and record the dipole moment; collect experimental values from CCCBDB.
Data analysis
Plot calculated against experimental dipole and compute errors; explain trends with the vector sum of bond dipoles and the molecular geometry.
How it works
You change Molecule and measure Calculated dipole moment (D) in Fluoromethanes (modelled), keeping Method, Basis set, Geometry optimised the same. Expect a graph of Calculated dipole moment / D against Experimental dipole moment / D: Points near a line of gradient 1 mean good agreement.
Make it yours
Compare two basis sets or methods and discuss cost versus accuracy.
Extended Essay angle
Benchmark several levels of theory systematically.
Safety
Computer only.
Data sources
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