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Unit 2: Topic 1 - Inter-molecular Forces (Inter-molecular Forces (Explain:…
Unit 2: Topic 1 - Inter-molecular Forces
Inter-molecular Forces
Predict:
The shapes of molecules with valence shell electron pair repulsion (VSEPR)
Assumes each atom in a molecule will achieve a geometry which minimises repulsion between electrons
Linear, trigonal planar, tetrahedral, trigonal pyramidal and bent molecules
Explain and Predict:
The polarity of molecules
Electronegativity
The tendency of an atom to attract a bonding pair of electrons within a covalent bond
The atom which pulls the electrons closer is more negative (weak so not ionic) and vice versa
Therefore in covalent molecules one side will be more negative vice versa, this creates a dipole
Sometimes the molecular shape has an impact (if symmetrical then charges cancel out & become non-polar)
Explain:
The relationship between observable properties and the nature and strength of intermolecular forces
Dipole-Dipole Bonding
Electrostatic forces of attraction between permanent dipoles (polar molecules)
Dispersion Forces
Occurs between non-polar molecules
Non-polar valence electrons can move freely which randomly creates dipoles
Extremely weak as it requires another molecule to also be experiencing a 'dipole moment' at the same time
Hydrogen Bonding
Specific type of dipole-dipole bonding with hydrogen (one of the most electropositve atoms)
Can bond with most electronegative atoms
Molecule Properties Based on Shape and Polarity
The stronger the IMF, the greater energy required to melt and boil/vaporise the molecules apart
Chromatography Techniques
Recognise:
That chromatography techniques can be used to determine the composition and purity of substances
Describe and Explain:
The mobile and stationary phases and how variations in interaction strength can be used to separate components
Analyse, Interpret and Evaluate:
Data from chromatographs to determine the composition & purity of substances (incl. calculating Rf values)