IMF Flashcards
What Does Molecular Shape Depend On
Number of atoms in molecule
Number of bonds from the central atom
Number of unbonded pairs of electrons around central atom
What Does VSEPR Theory Stand For
Valence Shell Electron Pair Repulsion Theory
What is the VSEPR Theory
Electron pairs in valence shell of atom repel each other
- So arranged as far apart as possible so they don’t repel, giving most stable configuration
- Repel because like charges repel
- Lone pairs repel other electrons more
- Electron pairs repel as far as possible, forming different molecular shapes
What are the 6 Molecular Shapes of Atoms
Trigonal Planar
Tetrahedral
Pyramidal
V-Shaped (Bent)
Linear (2 Atoms)
Linear (3 Atoms)
What is Trigonal Planar
3 atoms around the central atom
No unbonded pairs of electrons
Approx 120 degrees between each atom
What is Tetrahedral
4 atoms around the central atom
No unbonded pairs of electrons
Approx 109.5 degrees between each atom
What is Pyramidal
3 atoms around central atom
1 unbonded pair of electrons
Approx 109 degrees between each atom
What is V-Shaped (Bent)
2 atoms around central atom
Can have 1 unbonded pair, with approx 120 degrees between each atom
Can have 2 unbonded pairs, with approx 109 degrees between each atom
What is Linear (2 Atoms)
Diatomic molecules
Linear molecule, regardless of unbonded pairs
What is Linear (3 Atoms)
3 atoms in molecule
Approx 180 degrees between each atom
No unbonded pairs of central atom
Bonds on either side repel each other
How Do You Identify Molecular Shape From Formula
2 Methods:
Method #1:
1) Identify central atom
2) Identify umber of valence electrons in central atom
3) Identify number of bonding electrons in central atom
4) Identify number of lone electron pairs in central atom
5) Use properties of each molecular shape to determine
Method #2:
1) Draw electron dot diagram
2) Identify number of bonding & non-bonding pairs of electrons around central atom
3) State and explain the shape
What are Intermolecular Bonds
Bonds between different molecules
Weak bonds, have different types
Uses dotted line to draw
What are Intramolecular Bonds
Bonds within a molecule
Strong bonds, have different types (Covalent, Metallic, Ionic)
Uses full line to draw
Used to determine chemical properties of molecule
What is Polarity & Dipole
A molecule with imbalanced charge distribution is said to be polar
Dipole is the separation of positive and negative charges
How is Electronegativity Used to Predict Bond Polarity, where the two atoms have the same electronegativity
Predicts the polarity of the intermolecular bonds
If the 2 atoms have same electronegativities = Bond between them is non-polar
- As electrons shared equally between atoms, no dipole created
- Only diatomic molecules, as that’s the only way to have same electronegativity (Eg. O2)
How is Symmetry Used to Predict the Molecular Polarity, Where The Molecule is a Diatomic Molecule
Predicts the polarity of whole molecules
If the molecule is a diatomic molecule, depends on polarity of bond between those two atoms
- Polar bond = Polar molecule
- Non-Polar bond = Non-Polar molecule
What is the Polarity of a Bond where 2 Atoms Have Different Electronegativities
If the 2 atoms have different electronegativities = Bond between them is polar
- As electrons are closer to more electronegative atom, not equally shared
- More electronegative side is -ve charged, other side +ve charged, creating a dipole
- Higher difference in electronegativity = Higher polarity
How is Symmetry Used to Predict the Molecular Polarity, Where The Molecule is a Symmetrical Polyatomic Molecule
If the molecule is a polyatomic molecule and is symmetrical, is a non-polar molecule
- Non-Polar bonds don’t create any dipole, so they stay as they are
- The individual dipoles with the polar bonds cancel out perfectly, as the atom is symmetrical, creating a non-polar molecule
- “Not all molecules with polar bonds are polar”
How is Symmetry Used to Predict the Molecular Polarity, Where The Molecule is a Asymmetrical Polyatomic Molecule
If the molecule is a polyatomic molecule (More than 2 atoms) and is asymmetrical, is a polar molecule
- Has net dipole, charges don’t cancel each other out
- Has uneven charge distribution in molecule
- Must have polar bonds, as these polar bonds create a dipole
What are Dispersion Forces
Temporary/Instantaneous dipoles, where electrons have random movement around a molecule
Electrons eventually will gather closely at one end, becoming negative side, other side is positive side = Dipole
Electrons in next molecule are pushed to the far end due to electrostatic repulsion, creating another dipole
These dipoles are held together by attraction between the positive and negative dipoles of different molecules
What are properties of dispersion forces
High vapour pressure, as weak IMF, so molecules are held weakly on the surface, so easy to escape
Low melting and boiling point, weak IMF
Non-Polar to Non-Polar solubility, where dispersion forces between solute & solvent sufficient to disperse solute particles through solvent
What are Dipole-Dipole forces
Moderate vapour pressure, where it is a moderate IMF, so molecules are held moderately tight on surface, fairly hard to escape
Medium melting & boiling point, as moderate IMF
Is 10x weaker than Hydrogen Bonding
Polar to Polar solubility, where Dipole-Dipole forces between solute & solvent molecules strong enough to overcome solute-solute & solvent-solvent interactions
What is hydrogen bonding
Electrostatic attraction of hydrogen atoms bonded to Nitrogen, Oxygen, Fluoride (NOF) molecules, and their lone pairs
What is process of hydrogen bonding
1) Hydrogen bonded to NOF molecule
2) NOF molecule more electronegative, withdraws shared electrons = Dipole
3) Hydrogen has unshielded nucleus, also large magnitude positive dipole
4) Attracted to lone pairs of other NOF molecules (As they have negative dipoles, and lone pairs of electrons)
= Chain of Hydrogen bonds
What are properties of hydrogen bonding
Strongest IMF, relatively high melting & boiling point
Low vapour pressure, as strong IMF so molecules held tighter together, so harder to escape surface
Polar to Polar solubility, where Hydrogen bonding forces between solute & solvent molecules sufficient enough to overcome solute-solute and solvent-solvent interactions
How can you compare different IMF strengths
Higher boiling point = Stronger bond
- Boiling point is best indicator, as all bonds are broken at boiling point
Condensed state, only held by IMF forces
