12 Intermolecular Forces Flashcards
What is VSEPR theory
Valence She’ll Electron Pair Repulsion Theory states valence electron pairs in an atom repel one another and are positioned as far apart as possible
Define intermolecular forces
The attractive forces that arise between molecules in a substance and are responsible for physical and chemical properties of matter
What are the 5 shapes of molecules?
Linear - 180*
Trigonal planar - 120*
Tetrahedral - 109*
Bent
Trigonal pyramidal
What causes a bond to be bent?
If there are three things around the central atoms but one is a lone electron pair
What determines properties of covalent compounds?
The strength of the forces between molecules (intermolecular forces or bonds) which depends of the shape and covalent bonds inside molecules
What causes IMF to increase?
Increased melting point, boiling point, viscosity, solubility and surface tension
What is the relationship between IMF and vapour pressure?
IMF decrease when VP increases
Define vapour pressure
The pressure of the vapour present at equilibrium in a closed container
What are noncovalent intermolecular forces?
What are van der waals forces?
All intermolecular forces of attraction
What is electronegativity in reference to distribution
Tendency of an atom to attract electrons in a covalent bond. Determines the electron distribution of molecules
What are Non-Polar bonds
Formed between two identical atoms in a covalent bond, with a symmetrically positioned electron cloud
What are Polar bonds
Formed between two different atoms in a covalent bond, electrons might not be equally shared.
Uneven charge distribution.
skewed positioned electron cloud
What are dipoles
Comprised of two equal opposing charges separated by a distance
Symmetrical molecules polarity
In this molecule Individual bond dipoles cancel each other out and become non-polar eg methane
Types of intermolecular forces
Dispersion forces
Dipole dipole forces
Hydrogen bonds
What are dipole dipole forces
Wake attractive forces between polar molecules. The more polar the molecules, the stronger of the dipole dipole force. +I’ve and -I’ve ends of polar molecules attract.
Dispersion forces
Nonpolar molecules, where temporary dipoles can form because electrons in atoms are not always symmetrically distributed.
Strengths of dispersion forces
- large atoms have stronger dispersion forces
- large atoms have a larger number of electrons so are more likely to be asymmetrical
- more electrons means parcial charges on temporary dipoles are more likely to be larger
- strength increases down group
- shape of molecules
How weak r IMF
Intermolecular forces are 10-100 times weaker than bonds. They determine melting pts, boiling pts and vapour pressure
