Intermolecular Forces Flashcards
What are the 2 types of attraction in molecules?
Intramolecular and intermolecular forces.
What are intramolecular forces?
Forces of attraction within a molecule or ionic compound. (Holds atoms and ions together)
What are intermolecular forces?
Forces of attraction between molecules.
Which of INTRA and INTER mfs are stronger?
Intras are stronger.
What is happening when you boil water?
You are breaking the intermolecular forces.
Breaking the intermolecular forces does what?
Changes state.
What are the 3 kinds of intermolecular forces in order from weakest to strongest?
vanderwaals, dipole-dipole, H-bonds.
What are Vanderwaal’s forces?
Attractions between molecules that have temporary dipoles.
What are dipole-dipole forces?
Attractions between molecules that have permanent dipoles.
What is hydrogen bonding?
Attractions between molecules that contain very strong dipoles (H with N, O, or F).
Which intermolecular force occurs in all molecules.
Vanderwaals.
Why and how do Vanderwaals occur?
Because the electrons are moving around in atoms, so there will be instants when the charge around an atom is not symmetrical. This makes tiny dipoles which cause attraction between neighbouring atoms/molecules.
What factor increases the strength of Vanderwaals?
Size. Larger molecules have more protons and electrons.
Do larger molecules have higher or lower boiling points?
Higher
In a hydrocarbon chain, how does the number of carbons affect the boiling point?
As the number of carbons increase, the boiling point also increases.
How do Vanderwaals affect the halogens?
As you go down the halogens, their molar mass increases. This means they have more electrons and are harder to separate (higher boiling point).
What are 2 reasons why vanderwaals forces increase as molar mass increases?
With the molar mass, the number of electrons and the radius of the atom increase. The more electrons you have, and the more distance over which they can move, the bigger the possible temporary dipoles.
Why and how do dipole-dipole forces occur?
Polar substances have a slightly electronegative end and a slightly electropositive end. Dipole-dipole forces occur when oppositely charged poles momentarily attract one another.
What is the only intermolecular force that non-polar molecules have?
Vanderwaal
How does the electronegativity difference of the dipole moment affect the forces of attraction (dipole-dipole).
Greater EN means stronger dipole-dipole forces and higher boiling point.
Order HCl, HBr, and HI from highest boiling point to lowest.
HCl, HBr, HI
Why and how does hydrogen bonding occur?
N, O, and F are highly electronegative and have lone pairs of electrons which are attracted to H atoms in neighbouring molecules.
The hydrogen atoms in neighbouring molecules are essentially what?
Protons because of uneven sharing of the electron pair between H and NOF.
WHy are hydrogen bonds the strongest?
Because they have a much greater electronegativity than Dipole dipole forces.
How much stronger are Hydrogen bonds vs dipole dipole?
5 times stronger
What is misleading about the name “hydrogen bonding”?
It is not a real bond, since it is between molecules.
Out of COH, CCOH, and CCCOH, which is the most polar?
COH, because C is NP and OH is P. As the Carbon chain increases, the non-polar region becomes more significant, making the molecule less polar.
What is affected by the strength of IMFs between neighbouring covalent molecules?
The molecules’ boiling and melting points.
Its solubility in polar or nonpolar solvents.
When sharing electrons with H, what happens to the boiling point as you go down the group?
The molecule becomes stronger and has a higher boiling point. EXCEPTION: Even though O is the first in the group, H2O has the highest boiling point, because it has the ability to form H-bonds.
Why does the boiling point increase down a group (as period increases) ?
Electronegative difference and SIZE increase. Larger size means greater vanderwaals.
