UPCAT Chemistry — Molecular Theory — VSEPR, IMFA & KMTCheat Sheet
One-page cheat sheet for UPCAT Chemistry — Molecular Theory — VSEPR, IMFA & KMT. Every formula, definition, and key fact you need for this chapter, condensed to a single printable page. Designed for the final review session before the UPCAT 2026.
Exam context
On the UPCAT 2026, the Chemistry subtest carries a "Core" weight in University of the Philippines's pattern. Molecular Theory — VSEPR, IMFA & KMT lands at position 5th out of 7 in the standard review order. Target score is UPG ≤ 2.2 typical, and roughly 20 items come from Chemistry on a typical UPCAT paper.
Molecular Theory — VSEPR, IMFA & KMT - Cheat sheet
Your last-minute revision companion for mastering molecular geometry, intermolecular forces, and gas behavior before your UPCAT exam.
Sections
Formulas
Formula
Steric Number = Bonding pairs + Lone pairs
Meaning
Total electron pairs around central atom
Watch Out
Don't forget to count lone pairs - they affect shape!
When To Use
When determining molecular geometry
Common Values
Value
180°
Symbol
θ
Quantity
Linear bond angle
Value
120°
Symbol
θ
Quantity
Trigonal planar bond angle
Value
109.5°
Symbol
θ
Quantity
Tetrahedral bond angle
Section Title
VSEPR Theory (Valence Shell Electron Pair Repulsion)
Important Facts
- Lone pairs occupy more space than bonding pairs
- Bond angles decrease when lone pairs are present
- Double and triple bonds count as ONE electron pair
- Linear: 180°, Trigonal planar: 120°, Tetrahedral: 109.5°
- Lone pairs cause deviation from ideal bond angles
Key Definitions
Term
VSEPR Theory
Example
CH₄ has tetrahedral shape to minimize electron repulsion
Definition
Electron pairs repel each other and arrange themselves to minimize repulsion
Term
Steric Number
Example
NH₃ has steric number 4 (3 bonds + 1 lone pair)
Definition
Total number of electron pairs (bonding + lone) around central atom
Term
Electron Geometry
Example
NH₃ has tetrahedral electron geometry
Definition
3D arrangement of ALL electron pairs around central atom
Term
Molecular Geometry
Example
NH₃ has trigonal pyramidal molecular geometry
Definition
3D arrangement of atoms only (ignores lone pairs)
Diagrams To Know
- Lewis structures with electron pairs
- 3D molecular shapes for different steric numbers
- Bond angle diagrams showing electron repulsion
Formulas
Formula
Dipole moment = charge × distance
Meaning
μ = q × d (measure of molecular polarity)
Watch Out
Symmetrical molecules can have zero net dipole despite polar bonds
When To Use
Predicting strength of dipole-dipole forces
Common Values
Value
10-40 kJ/mol
Symbol
E
Quantity
H-bond energy
Value
5-25 kJ/mol
Symbol
E
Quantity
Dipole-dipole energy
Value
1-10 kJ/mol
Symbol
E
Quantity
London force energy
Section Title
Intermolecular Forces (IMFA)
Important Facts
- Strength order: Ion-dipole > H-bonding > Dipole-dipole > London forces
- Larger molecules have stronger London forces
- H-bonding requires H attached to N, O, or F
- Boiling point increases with stronger intermolecular forces
- Branching decreases intermolecular forces and boiling point
Key Definitions
Term
London Dispersion Forces
Example
Present in all molecules, strongest in large molecules like I₂
Definition
Weak forces due to temporary electron distribution imbalances
Term
Dipole-Dipole Forces
Example
HCl molecules attract each other through dipole-dipole forces
Definition
Attractions between permanent dipoles in polar molecules
Term
Hydrogen Bonding
Example
Water molecules form H-bonds: H₂O...H-O-H
Definition
Special dipole-dipole force when H bonds to N, O, or F
Term
Ion-Dipole Forces
Example
Na⁺ ion attracted to negative end of water dipole
Definition
Attraction between an ion and polar molecule
Diagrams To Know
- Hydrogen bonding patterns in water
- Dipole-dipole attraction diagrams
- London force temporary dipole illustrations
Formulas
Formula
KE = (3/2)kT
Meaning
Average kinetic energy of gas particles, k = Boltzmann constant, T = absolute temperature
Watch Out
Temperature MUST be in Kelvin, not Celsius!
When To Use
Relating temperature to molecular motion
Formula
PV = nRT
Meaning
Ideal gas law: P = pressure, V = volume, n = moles, R = gas constant, T = temperature
Watch Out
Use consistent units: atm-L or Pa-m³ for R value
When To Use
Calculating gas properties under ideal conditions
Common Values
Value
0.0821 L·atm/(mol·K)
Symbol
R
Quantity
Gas constant R
Value
8.314 J/(mol·K)
Symbol
R
Quantity
Gas constant R
Value
0 K = -273°C
Symbol
0
Quantity
Absolute zero
Section Title
Kinetic Molecular Theory (KMT)
Important Facts
- Gas particle volume is negligible compared to container volume
- No attractive forces between ideal gas particles
- Gas particles move in constant random motion
- All collisions are perfectly elastic
- Average kinetic energy depends ONLY on temperature
- Real gases deviate from ideal behavior at high pressure and low temperature
Key Definitions
Term
Ideal Gas
Example
No real gas is ideal, but noble gases at STP are close
Definition
Gas that perfectly follows KMT assumptions
Term
Elastic Collision
Example
Gas particles bounce off walls without losing energy
Definition
Collision where total kinetic energy is conserved
Term
Absolute Zero
Example
Theoretical temperature where gas volume becomes zero
Definition
Temperature where all molecular motion ceases (0 K = -273°C)
Diagrams To Know
- Maxwell-Boltzmann distribution curves at different temperatures
- Gas particle motion and collision diagrams
- Pressure vs temperature graphs for ideal gases
Reactions Or Equations
Note
Average kinetic energy per particle increases with temperature
Equation
KE_avg = (3/2)RT/N_A
Conditions
For one mole of gas particles
Must Remember
- VSEPR: Electron pairs repel and minimize repulsion
- Lone pairs take more space than bonding pairs
- Molecular geometry ignores lone pairs, electron geometry includes them
- H-bonding only with H attached to N, O, or F
- Intermolecular force strength: Ion-dipole > H-bond > Dipole-dipole > London
- KMT: Gas particles have negligible volume and no intermolecular forces
- Average kinetic energy depends ONLY on absolute temperature
- All gas collisions are elastic (energy conserved)
- Temperature must be in Kelvin for gas law calculations
- Real gases deviate from ideal at high pressure and low temperature
Last Minute Tips
- Draw Lewis structure first, then apply VSEPR to predict molecular shape
- Count lone pairs carefully - they're invisible but affect geometry
- For intermolecular forces: check for polarity first, then look for special cases like H-bonding
- In KMT problems, always convert Celsius to Kelvin (add 273)
- Remember: molecular motion never stops unless temperature reaches absolute zero
Comparison Tables
Rows
Values
- 2
- 0
- Linear
- Linear
- 180°
- CO₂
Property
2
Values
- 3
- 0
- Trigonal planar
- Trigonal planar
- 120°
- BF₃
Property
3
Values
- 2
- 1
- Trigonal planar
- Bent
- <120°
- SO₂
Property
3
Values
- 4
- 0
- Tetrahedral
- Tetrahedral
- 109.5°
- CH₄
Property
4
Values
- 3
- 1
- Tetrahedral
- Trigonal pyramidal
- <109.5°
- NH₃
Property
4
Values
- 2
- 2
- Tetrahedral
- Bent
- <109.5°
- H₂O
Property
4
Columns
- Steric Number
- Bonding Pairs
- Lone Pairs
- Electron Geometry
- Molecular Geometry
- Bond Angle
- Example
Table Title
VSEPR Molecular Geometries
Rows
Values
- Weakest
- All molecules
- 1/r⁷
- Br₂, CH₄
Property
London Dispersion
Values
- Moderate
- Polar molecules only
- 1/r³
- HCl, SO₂
Property
Dipole-Dipole
Values
- Strong
- H bonded to N, O, F
- 1/r²
- H₂O, NH₃, HF
Property
Hydrogen Bonding
Values
- Strongest
- Ions + polar molecules
- 1/r²
- NaCl in water
Property
Ion-Dipole
Columns
- Force Type
- Strength
- Molecules Involved
- Distance Dependence
- Example
Table Title
Intermolecular Forces Comparison
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