Chem Module 2

Question 1

Quantization

Answer 1

When an electron is ‘confined’ to a finite region of space by the forces exerted on it
- total energy is restricted t certain values

Question 2

Light and its three fields

Answer 2

electromagnetic radiation that transmits energy through space/medium, travels in waves
- electric field, magnetic field, direction that oscillate perpendicular to eachother

Question 3

wavelength

Answer 3

distance between adjacent maxima

Question 4

period

Answer 4

time for electric field to return to its max strength

Question 5

frequency

Answer 5

related to period , 1/T

Question 6

The electromagnetic spectrum in increaing wavelength (decreasing frequency )

Answer 6

gama rays, x rays, ultraviolet, visible, infrared, microwave, radiowaves

Question 7

Range of visible region in nm

Answer 7

from 400 to 750 nm

Question 8

visible spectrum and their colours

Answer 8

• violet (400)
• indigo
• blue
• green (570)
• yellow
• orange
• red (750)

Question 9

3 experiments that support the concept of energy being quantized at the molecular level

Answer 9

1. Blackbody Radiation
2. The Photoelectric Effect
3. Line Spectra of Atoms

Question 10

Blackbody Radiation

Answer 10

• atoms in a heated solid osciallte with certain energies only
• Energy of oscillation = nhv

Question 11

Max Planck

Answer 11

First suggestion of quantization of energy , quanta of energy are absorbed by and emitted from matter
- Frequency : v=c/landa
- Energy: E = nhv (h is an constant , v is frequency)
- plancks constant

Question 12

The photoelectric effect

Answer 12

• Energy of light is highly localized and is proportional to its frequency
• light can produce and electric current
• discovered by having electrons dislodge from the surface of a metal

Question 13

Observations of the photoelectric effect

Answer 13

• electrons were ejected only if the frequency of light was greater than some “threshold” frequency
• ejected electron increased proportionally with frequency
• energy of the light must be highly localized in space and not spread out over the entire wave
• proportionality constant between frequency and energy is equal to Planck’s constant

Ephoton =hv

Question 14

Line Spectra of atoms

Answer 14

Energy of an electron in an atom is not arbitrary , restricted to certain special values.
- absorbed or emitted colours show that atoms absorb or emit photons with certain specific energies - emission lines

Question 15

Problems with the Bohr Model

Answer 15

• doesn’t explain why the angular momentum and energy of the electron is quantized
• model not extended to other atoms
• why doesn’t the H atom emit radiation continuously?

Question 16

2 solutions to the limitations of the Bohr Model (behaviour of electrons)

Answer 16

1. de Brogile’s hypothesis
2. the Heisenberg uncertainty principle

Question 17

de Brogile’s hypothesis

Answer 17

particles exhibit wave-particle duality by understanding
- diffraction (light behaving as a wave)
- The photoelectric effect (light behaves as particles)

experiment: diffraction pattern produced by constructive and destructive interference of light waves

Question 18

Heisenberg uncertainty principle

Answer 18

we can never know the true behaviour of a system
- if we tried to measure the position of an electron, we will change its momentum

Question 19

n quantum number

Answer 19

principal quantum number - determines size of orbital (any integer)

Question 20

l quantum number

Answer 20

orbital angular momentum quantum number - determines the shape of an orbital (n-1)

Question 21

ml quantum number

Answer 21

magnetic quantum number - the number of distinct orientations allowed for a particular orbital (-l to +l)

Question 22

Radial factors, what does it describe and its axis

Answer 22

R(r) and r, how the wave function changes w distance from nucleus

Question 23

Radial electron density, what does it describe and its axis

Answer 23

R(r)^2 and r, probability of finding electron changes as we move away from the nucleus

Question 24

Radial Distribution plot, what does it describe and its axis

Answer 24

r^2(R)r^2 and r, average distance between nucleus and electron

Question 25

Significance of Schrodinger equation

Answer 25

describes the behaviour of a single electron moving about the nucleus in the H atom