Unit 3 Flashcards
#1 to review
Intramolecular force
A covalent bond- holds atoms together within a molecule
Intermolecular force
Interaction between two different molecules
Difference in strength from ionic/covalent bonds to IMFs?
IMFs are weaker
Are water molecules polar or non polar?
Polar: partial negative charge on the oxygen and a partial positive on the Hydrogens
When do dipole dipole ints occur?
Any two polar molecules
What can dipole dipoles be?
Attractive or repulsive
How do molecules generally orient themselves?
To maximize attraction
What determines the strength of dipole dipole interactions?
The magnitude of the dipole is directly related
What are some examples of dipole dipole interactions?
CO, NH3, CH2Cl2
What are dipole induced dipoles? What are they ALWAYS?
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
How are temporary dipoles forned in NP molecules?
The electrons randomly fluctuate, creating TEMPORARY dipoles
Explain how temporary dipoles in a NP molecule can affect another NP molecule that it approaches.
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
What are attractions caused by temporary dipoles called?
London Dispersion Forces
What do the strength of LDFs depend on?
The dispersion of the electron cloud
Larger cloud –> more polarizable –> greater LDF strength
What happens to the boiling point when the electron cloud becomes larger?
They increase because of increased LDFs
What does a higher Hvap mean?
Molecules are experiencing higher IMFs regardless of type
What gives H2O, a small molecule, a higher boiling point than H2S, a larger molecule with stronger LDFs?
H2O can hydrogen bond
How does hydrogen bonding work?
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
What are the only atoms that can hydrogen bond?
An H covalently bonded to N, O, or F, AND a highly EN atom on another molecule
How can H bonding happen IN THE MOLECLE?
The atoms must be far enough apart in the molecule in order to “reach”
Explain ion dipole interaction.
Ionic compounds dissolve in an Aqueous solution –> the dipole of water interacts with the ions and makes them separate
What are ion dipole interactions stronger than?
Hydrogen bonding
What properties of substances are explained by IMFs?
Melting/boiling pt
Vap pressure
Volatility
Surface Tension
Viscosity
Heat of Vap
Which properties increase as IMFs increase?
Melting/boiling pt
Surface tension
Viscosity (resistance to flow)
Heat of vap (energy to go from liquid –> gas)
Which properties decrease as IMFs increase?
Vap pressure (pressure of gas when at eq with liquid)
Volatility (ease of evaporation)
How to compare IMF magnitude in 2 diff substances?
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
Properties of solids
- Very strong particle interactions
- Definite shape and volume
- Regular, crystalline structure
- Fixed arrangement of particles
- Vibrational degree of freedom
Ionic solid properties
- Cation and anions in a 3D Lattice held together by lattice energy
- Formula reps ratio between ions, not discrete particles
- HIGH MELTING and BOILING points due to strong coulombic attractions
- Brittle - can shift ions in place –> repulsion –> breakage
- Poor conductors of electricity when solid, but good when liquid and aqueous (ions must be free to conduct)
Molecular solid properties
- Individual neutral molecules fixed into molecular lattice structures
- made of NM atoms, the formula reps the actual # of atoms int he molecule
- Weak IMFs = Low melting and boiling pt
- Poor conductors of electricity due to electrons held tightly in covalent bonds
Covalent network solid properties
- Distinct atoms bonded in covalent 3D network
- Formed by carbon or metalloids (silicon, germanium, boron)
- SUPER high melting pt and hardness
- Poor conductors due to tightly held electrons in covalent bonds
How is graphite (solid carbon) different from diamond (solid Carbon)
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
Metallic solid properties
- Formed by metallic elements
- Free flow of VEs between atom to atom
- Great conductors of heat and electricity
- malleable
- ductile (can stretch)