Forces between molecules Flashcards
What bonds hold atoms in molecules and in giant structures
Atoms in molecules and in giant structures are held together by strong covalent, ionic or metallic bonds
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 act only between certain types of molecules
hydrogen bonds act only between certain type of molecules
What is the rank order of strength between van der Waals, dipole - dipole forces and hydrogen bonds?
1) van der Waals - weakest
2) dipole - dipole forces - medium
3) hydrogen bonds - strongest
If a molecule has more than one polar bond, what occurs commonly? If a molecule has more than one polar bond what main 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.
If a molecule has more than one polar bond, the effects may add up and reinforce each other, but this depends on the shape of the molecule
When two polar molecules have dipoles, what occurs?
Two polar molecules that both have dipoles will attract one another. No matter their starting positions, molecules with dipoles will ‘flip’ to make an arrangement where the two molecules attract
What are van der Waals?
van der Waals are a type of intermolecular forces which are formed fromt he positive and negative charges between atoms, which 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 as the electron distribution of the original 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 the electron cloud
What is the name given to the forces created by the change of electron distribution of the original atom?
These forces created are called instantaneous dipole - induced 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
Van der Waals increase in size with the number of electrons, what does this mean for atoms/molecules with smaller/larger masses?
Atom and molecules with larger atomic or molecular masses produce stronger van der Waals forces than atoms and molecules with small atomic or molecular masses
What is a hydrogen bond?
A hydrogen bond consists of a hydrogen atom sandwiched between two very electronegative atoms
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
