Forces between Molecules Flashcards
What are intermolecular forces?
weak forces of attraction between molecules
What are the three types of intermolecular forces?
-van der Waals forces
-dipole-dipole forces
-hydrogen bonding
Put each intermolecular force in order of strongest to weakest
hydrogen > dipole-dipole > van der Waals
What are van der Waals forces?
weak electrostatic attraction produced by positive and negative charges
Where do van der Waals forces occur?
between all atoms and molecules
What affects the strength of van der Waals forces?
increase with number of electrons
What atoms produce strong van der Waals forces?
those with large atomic masses
What molecules may have a dipole moment?
those with polar bonds
In which molecules do dipoles cancel?
linear and tetrahedral molecules
What is a dipole caused by?
changing position of electron cloud
What do dipoles affect?
electron distribution in nearby molecules, can induce temporary dipoles
Where do dipole forces act?
between molecules with permanent dipoles
What will dipoles do so that two molecules attract?
flip their arrangement
What does a hydrogen bond consist of?
hydrogen atom between two very electronegative atoms
What conditions are required for hydrogen bonding to occur?
- very electronegative atom with lone pair
- connected covalently to hydrogen atom
How can hydrogen bonding occur in water?
-oxygen atom is highly electronegative
-oxygen has a lone pair
-hydrogen atoms electron deficient due to oxygen high electronegativity
How is a hydrogen bond shown?
a dashed line - - -
How is hydrogen charged in a water molecule?
delta plus / partially positive
How is oxygen charged in a water molecule?
delta minus / partially negative
How does hydrogen bonding affect the boiling points of the hydrides?
generally noble gases shown increase in boiling point as van der Waals forces increase with number of electrons
HOWEVER…
boiling points of H2O, HF and NH3 are higher due to strength of hydrogen bonds
