Intermolecular Forces Flashcards
What is electronegativity?
Ability of an atom to pull electrons towards itself
What do atoms with a higher electronegativity do?
Pull electrons more strongly towards itself
What is periodic property?
Dependency on. the position of an element on the periodic table
What are the different types of factors which affect electronegativity?
Nuclear charge
Atomic radius
Electron shielding
What do you have to have to have a high electronegativity in terms of :
Nuclear charge
Atomic radius
Electron shielding
A higher nuclear charge
A small atomic radius
A low amount of shielding
Can you predict whether the bonding of molecules will ionic or covalent?
Yes by calculating the different in values of electronegativity
Is it more likely to be an ionic or covalent bond if the difference of electronegativity is greater than 1.7?
Ionic
Is it more likely to be an ionic or covalent bond if the difference of electronegativity is less than 1.7?
Covalent
What is the electronegativity between hydrogen and chloride?
0.9
Why is hydrogen chloride special?
- In its gaseous form, hydrogen and chlorine are covalently bonded
- In aqueous form, it ionises completely to give H+ and Cl- (Hydrochloric acid) form has a polar covalent bond
Finish the sentence:
If two atoms of the same element form a covalent bond, the distribution of electrons in molecular orbitals is …..
symmetrical
What happens if different atoms forms bonds?
- Asymmetrical distribution of electrons in molecular orbitals
- Different electronegativities
- Different ability to attract electrons
Why is the carbon-chlorine bond polar?
- Chlorine more electronegative than carbon
- Gives an unsymmetrical bonding molecular orbital
- Which can be illustrated with partial charges d+ and d-
- The bond has a dipole
What is a permanent dipole?
Small charge difference across a bond that results from a difference in the electronegativities of the bonded atoms
Is a carbon-hydrogen bond polar or not polar?
Not polar
- but the molecule its self is polar and overall there is a permanent dipole
How can the overall dipole on a molecule be reinforced or reduced?
Determined by the orientation if the bonds
Are ionic and covalent intermolecular forces?
Yes
-Bonds occur between atoms
What is an intermolecular force?
Occurs between atoms
- Difference in electronegativity values between atoms
- Polarity of molecules
What happens to the boiling point if you have a strong intermolecular forces?
High boiling point therefor high melting point
Wha are the three types of intermolecular forces?
- Dipole-dipole interactions
- van-der Waals forces
- Hydrogen bonds
What are dipole-dipole reactions?
Molecules with a permanent dipole attack each other
-Due to electronegativity differences
Are dipole-dipole weak or strong intermolecular forces?
Weak but still impact e.g boiling point
What is required when going from liquid to vapour phase?
Breakage of intermolecular attractions
How does dipole-dipole interactions affect solubility?
Interaction between molecules with permanent dipoles enables such compounds to dissolve
What are van-de Waals forces?
Interaction between molecules which do not have a permanent dipole (therefor induced dipoles)
How do you get van-de Waals forces?
- Electrons not beings stationary (EVEN IN SYMMETRICAL MOLECULES)
- Leads to a small temporary dipole
- Which induces a small temporary dipole in an adjacent molecules
Do larger molecules (have more electrons) have more or less temporary dipoles?
More
If more temporary dipoles is the attired force less or greater?
Greater
If the molecules are further apart are the forces stronger or weaker?
Weaker
What are van-her Waals forces vital in?
Maintaining lipid bilayer of a cell membrane
Protein structure
What are hydrogen bonding?
- Occurs when a hydrogen atom is attached to an electronegative atom, usually oxygen or nitrogen
- This hydrogen atom is also attracted to another electronegative atom
Is hydrogen the strongest intermolecular interaction?
Yes
Is hydrogen bonding possible in ethanol?
Yes
Is hydrogen bonding possible in diethyl ether?
No
Does hydrogen have many vital biological roles?
Yes - complementary base pairing
Are protein dependent on H-bonding for structure?
Yes - enzyme substrate binding
Order dipole-dipole interaction, van-der Waals force and hydrogen bonding in weakest to strongest?
van-der Waals forces
Dipole-dipole interaction
Hydrogen bonding
What is solubility?
Two substances will mix completely (or a solute will dissolve in a solvent if some of intermolecular attraction between the molecules after mixing are greater than the some of intermolecular attractions before mixing
What is salvation?
Two compounds mixing together
Do compounds that show extensive hydrogen bonding dissolve in water?
Yes
What doe hydrocarbons really on?
Van der Waals forces for intermolecular attractions
Are hydrocarbons soluble in water?
No
If the longer the alkyl chain in water are there more or less van der Waals forces?
More causing water solubility to drop
Can changes in intermolecular interactions give solubility?
Yes
