Unit 3

Question 1

Intramolecular force

Answer 1

A covalent bond- holds atoms together within a molecule

Question 2

Intermolecular force

Answer 2

Interaction between two different molecules

Question 3

Difference in strength from ionic/covalent bonds to IMFs?

Answer 3

IMFs are weaker

Question 4

Are water molecules polar or non polar?

Answer 4

Polar: partial negative charge on the oxygen and a partial positive on the Hydrogens

Question 5

When do dipole dipole ints occur?

Answer 5

Any two polar molecules

Question 6

What can dipole dipoles be?

Answer 6

Attractive or repulsive

Question 7

How do molecules generally orient themselves?

Answer 7

To maximize attraction

Question 8

What determines the strength of dipole dipole interactions?

Answer 8

The magnitude of the dipole is directly related

Question 9

What are some examples of dipole dipole interactions?

Answer 9

CO, NH3, CH2Cl2

Question 10

What are dipole induced dipoles? What are they ALWAYS?

Answer 10

When a dipole of water (neg charged O) approaches the NP O2 molecule: The O2 is repelled by the negative part of the water, so it is forced to form a dipole (Pos charge on one O atom)

THEY ARE ALWAYS ATTRACTIVE

Question 11

How are temporary dipoles forned in NP molecules?

Answer 11

The electrons randomly fluctuate, creating TEMPORARY dipoles

Question 12

Explain how temporary dipoles in a NP molecule can affect another NP molecule that it approaches.

Answer 12

Temporary dipole of one molecule approaches another –> electrons in second molecule are repelled by NEG pole and attracted to POS pole –> this polarizes 2nd molecule –> attraction between the two

Question 13

What are attractions caused by temporary dipoles called?

Answer 13

London Dispersion Forces

Question 14

What do the strength of LDFs depend on?

Answer 14

The dispersion of the electron cloud

Larger cloud –> more polarizable –> greater LDF strength

Question 15

What happens to the boiling point when the electron cloud becomes larger?

Answer 15

They increase because of increased LDFs

Question 16

What does a higher Hvap mean?

Answer 16

Molecules are experiencing higher IMFs regardless of type

Question 17

What gives H2O, a small molecule, a higher boiling point than H2S, a larger molecule with stronger LDFs?

Answer 17

H2O can hydrogen bond

Question 18

How does hydrogen bonding work?

Answer 18

A highly EN O atom draws electrons to itself away from H atoms –> A “bare” H proton is left since its electrons are pulled away –> another highly En O atom from a different water molec interacts strongly with this H atom and forms the H bond

Question 19

What are the only atoms that can hydrogen bond?

Answer 19

An H covalently bonded to N, O, or F, AND a highly EN atom on another molecule

Question 20

How can H bonding happen IN THE MOLECLE?

Answer 20

The atoms must be far enough apart in the molecule in order to “reach”

Question 21

Explain ion dipole interaction.

Answer 21

Ionic compounds dissolve in an Aqueous solution –> the dipole of water interacts with the ions and makes them separate

Question 22

What are ion dipole interactions stronger than?

Answer 22

Hydrogen bonding

Question 23

What properties of substances are explained by IMFs?

Answer 23

Melting/boiling pt
Vap pressure
Volatility
Surface Tension
Viscosity
Heat of Vap

Question 24

Which properties increase as IMFs increase?

Answer 24

Melting/boiling pt
Surface tension
Viscosity (resistance to flow)
Heat of vap (energy to go from liquid –> gas)

Question 25

Which properties decrease as IMFs increase?

Answer 25

Vap pressure (pressure of gas when at eq with liquid)
Volatility (ease of evaporation)

Question 26

How to compare IMF magnitude in 2 diff substances?

Answer 26

Same # electrons (so same mass usually): Hyd bond > di-di > LDF

Diff electrons/same IMFs = larger molecule has stronger IMFs

Diff sizes/DIff IMFs = Compare boiling points

Question 27

Properties of solids

Answer 27

1. Very strong particle interactions
2. Definite shape and volume
3. Regular, crystalline structure
4. Fixed arrangement of particles
5. Vibrational degree of freedom

Question 28

Ionic solid properties

Answer 28

1. Cation and anions in a 3D Lattice held together by lattice energy
2. Formula reps ratio between ions, not discrete particles
3. HIGH MELTING and BOILING points due to strong coulombic attractions
4. Brittle - can shift ions in place –> repulsion –> breakage
5. Poor conductors of electricity when solid, but good when liquid and aqueous (ions must be free to conduct)

Question 29

Molecular solid properties

Answer 29

1. Individual neutral molecules fixed into molecular lattice structures
2. made of NM atoms, the formula reps the actual # of atoms int he molecule
3. Weak IMFs = Low melting and boiling pt
4. Poor conductors of electricity due to electrons held tightly in covalent bonds

Question 30

Covalent network solid properties

Answer 30

1. Distinct atoms bonded in covalent 3D network
2. Formed by carbon or metalloids (silicon, germanium, boron)
3. SUPER high melting pt and hardness
4. Poor conductors due to tightly held electrons in covalent bonds

Question 31

How is graphite (solid carbon) different from diamond (solid Carbon)

Answer 31

SP2 hybridized –> forms large sheets in trigonal planars –> weak IMFs allow layers to slide past one another

EXCELLENT CONDUCTOR OF ELECTRICITY due to delocalized electrons flowing across sheets of aligned p orbitals

Question 32

Metallic solid properties

Answer 32

1. Formed by metallic elements
2. Free flow of VEs between atom to atom
3. Great conductors of heat and electricity
4. malleable
5. ductile (can stretch)