3.1-3.3 Quiz Flashcards
London Dispersion Forces(LDFs)
- Definition
- What type of substances have LDFs?
- The result of Coulombic interactions between temporary, fluctuating dipoles.
- All substances have LDFs. They are the only force in nonpolar molecules or single nonmetal atoms.
What is the strongest IMF between large molecules?
LDFs
How does the polarizability of a molecule increase and why?
The polarizability of a molecule increases when the number of electrons in a molecule increases because larger atoms have more loosely held electrons in contrast to smaller atoms with tightly bound electrons.
Dipole-dipole interactions
- When do they occur?
- What substances have dipole-dipole?
- How do they increase?
- They occur between polar molecules.
- All polar molecules have dipole-dipole.
- When the difference in electronegativity is greater then the dipole is stronger
Are polar molecule interactions greater than nonpolar molecule interactions? Why or why not?
Yes because polar molecule interactions act in addition to LDFs.
Hydrogen bonding
- Where does it exist?
- The hydrogen has to be covalently bonded to NOF and then bonded to NOF through an intermolecular force. Technically it has to occur between molecules not within, but if it occurs within it needs to be far apart.
Intermolecular forces vs intramolecular forces
Inter- between molecules(H2 —- H2)
Intra- between atoms( H- - - O - H—-O)( dotted lines)
Weakest to strongest IMFs
Molecular(LDFs, Dipole-Dipole, Hydrogen Bonding), Ionic/Metallic, Covalent Network
Ionic interactions
- Description/Definition
- In what substances do these occur?
- When are ionic bonds stronger?
- Metal and nonmetal atoms form a lattice of alternating positive and negative ions held
together by ionic bonds - When metals bond with nonmetals when they lose or gain electrons to form ions.
- They are stronger when the charges are larger and the ions are smaller.
Covalent network
- Description/Definition
- Name the atoms that will have a covalent network.
- How do these increase?
- Nonmetal atoms form a lattice structure held together with covalent bonds.
- (BASICALLY ATOMS WITH C AND METALLOIDS(LIKE SILICON, GERMANIUM, BORON, ETC.)) C(diamond), C(graphite), C60, SiO2, SiC
- When there are more covalent bonds formed(two nonmetals)
Polarizability
The ability of an atom to form a temporary or induced dipole
When going down the list of halogens they change in state from gas to liquid to solid. Why does this happen?
This is because the LDFs increase and the LDFs increase due to the increase in electrons. Also, larger molecules will have stronger LDF because the increase in electrons increases their polarizability.
Name the way LDFs increase.
They increase with increasing contact area(meaning the bigger it is(more electrons it has)) between molecules and with increasing polarizability of the molecules. Also, long thin molecules have more surface area, stronger LDFs, and stronger polarizability. Short round/compact molecules have less surface area, weaker LDFs, and weaker polarizability. Lastly, the presence of double or triple bonds.
How are LDFs caused?
They are caused by the motion of electrons within an atom or molecule. As the electrons move around with the atom, the electrons sometimes become unequally distributed and the atom or molecule creates a temporary dipole because there is an excess of negative charge in one place and an area that is partially positive because it is deficient in electrons. This is a short lived thing which is why this is such a weak force.
Hydrocarbon
Only hydrogens and carbon
The amount of energy needed to melt a substance at its melting point is called the heat of fusion and for
water the value is 6.01 kJ/mol. The amount of energy needed to vaporize a substance at its boiling point is
called the heat of vaporization and for water the value is 40.7 kJ/mol. Use the relative distances in the
states of matter and the concepts intermolecular forces to explain the difference.
Solid to a Liquid is a slight distance increase, however Liquid to a Gas is a large distance increase because spreading the molecules apart takes a lot of energy.
Surface tension
ability of the surface of a liquid to resist an external force
Viscosity
resistance to flow