Midterm Test

Question 1

Wavelength (lambda)

Answer 1

Distance between two peaks or two roughs (measured in m or nm)

Question 2

Frequency (v, nu)

Answer 2

Number of waves that pass through a given point . (units S-1, HZ)

Question 3

Constructive vs deconstructive

Answer 3

Waves interfere, do not need to be the exact same.

Question 4

E = h*v

Answer 4

h = Plank’s constant (6.626*10^-24 J/S
E = E photon (= E binding + KE)
V = frequency

= hc/wavelength
C = constant (3x10^8 m/s)

Question 5

Diffraction

Answer 5

Electrons diffract.

Question 6

Emission of light from atoms

Answer 6

Passage of electricity through gas of atoms causes atoms to emit light.

• Only see 4 frequencies on the detecting screen
• Discrete emission lines can only be explained by quantisation of the energy levels of atoms and molecules

Question 7

Schrödinger model of the atom

Answer 7

H * Ψ = E * Ψ

H = hamiltonian
E = energy
Ψ = wavelength or orbital = a mathematical function describing the shape of a wave
Ψ^2 = Probability of finding and electron at any point around the nucleus,eaus

Question 8

Quantum Numbers of Atomic Orbital

Answer 8

1. Principle quantum number (n) - size of orbital
2. Angular momentum quantum number (l) = (n-1)- shape of orbital
3. Magnetic quantum number (ml or m) - orientation of orbital (-l <-> +l)
4. Electron spin quantum number (ms or s) = +/- 1/2

Question 9

Radial probability

Answer 9

Distribution, sum of all Ψ^2

Question 10

Schrödinger model: Energies of orbitals

Answer 10

HΨ = EΨ

E_n = -2.18x10^-18 J *(1/n^2) -DOES NOT depend on l or m

• Subshells have the same energy (they are degenerate)
  E = how stable the orbital is having the probability Ψ

Question 11

Pauli exclusion principle

Answer 11

No two electrons in an atom can have the same value of all 4 quantum numbers

Question 12

Factors determining an atom’s energy

Answer 12

1. Electron-nucleus attractions
2. Electron-electron repulsions - electrons further from the nucleus are shielded from full + nuclear charge by electrons closer to nucleus

Zeff = “effective” nuclear charge
= Z actual - shielding electrons

Ens < Enp < End < Enf
<——– higher zeff

Question 13

Hund’s Rule

Answer 13

If two or more degenerate orbitals are available, one electron goes into each until they are half full. All half fulled orbitals have the same spin quantum number.

Question 14

Non-directional solid

Answer 14

Ionic solids form because oppositely charged ions are attracted to each other in all directions.

Question 15

Electronegativity

Answer 15

The ability of an atom in a molecule to attract electrons toward itself.

Question 16

Types of Bonding

Answer 16

1. Non-polar covalent (En difference = 0) i.e. H2 - Electronically symmetrical
2. Polar covalent (En difference <=2.0) i.e HF - partial charges
3. Ionic (En difference >=2.0) i.e. LiF - full charges, metal + non-metal

Question 17

VSEPR Model

Answer 17

1. Linear (180º - 2)
2. Trigonal Planar (120º -3)
3. Tetrahedral (109.5º - 4)
4. Trigonal Bipyramidal (90º and 120º - 5 “seesaw”)
5. Octahedral (90º - 6)

Question 18

Dipole Moment

Answer 18

A measure of the separation of charge in a molecule arising from the unequal sharing of electrons in polar bonds.

No dipole moment = non-polar
Permanent molecule = polar

Question 19

Ion-dipole Interaction

Answer 19

(only for mixtures)
Interaction between fully charges ion and partial charges of a polar molecule
- The energy of attraction increases with the charge of the ion and decreases with the square of the distance between ion and dipole

Question 20

Dipole-dipole interaction

Answer 20

Polar molecules attract one another when they orient with unlike charges close together, but they repel one another when they orient with like charges together.

Question 21

Hydrogen-Bonding

Answer 21

Dipole-dipole interactions between H and very electronegative elements N and O. I.e. DNA nucleotide base pairs.

Question 22

London dispersion forces

Answer 22

Occurs between all molecules, strength depends on size, polarisability.

Question 23

Pressure

Answer 23

Force exerted per area
P = F/A

Units Pa = N/m^2; kPa = 10^3 Pa
1 atm = 760 mmHg

Question 24

Kinetic Molecular Theory

Answer 24

1. Gases made of tiny particles moving completely randomly
2. Total volume of particles very small compared to size of container
3. Particles do not interact with each other
4. Particle collisions are elastic
5. Kinetic Energy increases with temperature

Question 25

Effusion

Answer 25

Escape of a gas through a hole into a vacuum

Question 26

Crystalline Solids

Answer 26

Well-ordered matter within the solid arrangement of atoms in the solid repeats solids.
4 types: molecular, ionic, covalent network, metallic

Question 27

Amorphous Solids

Answer 27

Don’t have extensive ordering of particles.

Question 28

Allotropes

Answer 28

Different structural forms of an element.

Question 29

Covalent Network Solids

Answer 29

extended structure of atoms held together by covalent bonds.

Question 30

Metallic Solids

Answer 30

Metal atoms as cations in sea of “delocalised” electrons.

Question 31

Ionic Solids

Answer 31

Held together by electrostatic attraction between cations and anions.

Question 32

Cohesive vs adhesive forces

Answer 32

Cohesive: Between molecules (IMFs)
Adhesive: Between molecules and container walls.

Question 33

Colligative Properties

Answer 33

Solution properties that depend on concentration of solute, not its identity.

Question 34

Osmotic Pressure

Answer 34

Pressure that must be applied to a solution to prevent osmosis from a sample of pure solvent.

Question 35

Vapor pressure

Answer 35

Non-volatile solutes decrease vapour pressure of solvent.

Raoult’s Law for non volatile solute:
P = XPº
P = vapor pressure of solvent
X = mole fraction of solvent
Pº = vapor pressure of pure solvent