Forces between molecules Flashcards
(15 cards)
How many types of intermolecular forces are there? What are the names of all the intermolecular forces?
There are three intermolecular forces;
1) van der Waals
2) dipole - dipole forces
3) hydrogen bonds
What do van der Waal forces act between?
What do dipole - dipole forces act between?
What do hydrogen bonds act between?
van der Waals act between all atoms and molecules
dipole - dipole forces and hydrogen bonds act only between certain type of molecules
Rank order the strength of the intermolecular forces between:
van der Waals
dipole - dipole forces
hydrogen bonds
1) hydrogen bonds - strongest
2) dipole - dipole forces - medium
3) van der Waals - weakest
If a molecule has more than one polar bond, what occurs commonly?
What may also occur depending on the shape of the molecule?
If a molecule has more than one polar bond there may not be a dipole moment, as the effect of each bond may cancel eachother
Depending on the shape of the molecule, the effects may add up and reinforce eachother
When two polar molecules have dipoles, what occurs?
They become attracted to one another. They will then rotate to make an arrangement allowing the attraction to occur
What are van der Waals forces?
van der Waals are a type of intermolecular forces formed between the positive and negative charges of atoms to produce very weak electrostatic attractions between all atms and molecules
What is a temporary dipole + how does it occur?
A temporary dipole occurs when an arrangement is formed within an atom resulting in a dipole, temporary dipoles are dipoles that happen just for an instance
Describe what happens to other atoms as the electron distribution of an atom changes
As the electron distribution of the original atom changes, atoms around it will be induced to form dipoles, that will be attracted to the original atom
What is the cause of a dipole?
Dipoles are caused by the changing positions of electron distribution
The name given to the force created by the change of electron distribution of the original atom?
Instantaneous dipole/ Induced dipole - dipole forces
What causes the size of van der Waals to increase?
The size of van der Waals increases with the number of electrons present
How does a hydrogen bond occur?
A hydrogen bond occurs when the lone pair electrons on an atom is strongly attracted to the electron deficient hydrogen atom to form a strong intermolecular force
What two requirements are needed in order for a hydrogen bond to form
1) A hydrogen atom with a strong partial positive charge
2) A very electronegative atom with lone pair of electrons to be attracted to the partially charged hydrogen atom
What are the only atoms that are electronegative enough to form hydrogen bonds?
Fluorine
Nitrogen
Oxygen
Why do the boiling points of noble gases increase?
The boiling points in noble gases show gradual increase in boiling points because the only forces acting between atoms are van der Waal forces which increase with the number of electrons present
