M8 Topic 3: Quantum Mechanical Nature of the Atom

Question 1

What were the limitations of Rutherford’s planetary model (2)

Answer 1

• could not explain why electrons did not lose energy and spiral into the nucleus as they were accelerating
• could not explain the structure of the nucleus

Question 2

Who was the third person to change the atom model

Answer 2

Niels Bohr (1911)

Question 3

How did Niels Bohr change the Rutherford’s atom model (3)

Answer 3

Bohr’s Postulates

• Electrons orbit the nucleus in clearly defined energy states called orbitals and therefore could not radiate energy.
• Any transition between states involved the absorption and emission of a discrete amount of energy.
• The angular momentum of electrons in each orbital is quantised. (meaning they could not exist in between these orbitals)

Question 4

Who discovered proof of energy levels

Answer 4

Thomas Melvill

Question 5

How did Melvill find proof of energy levels and what did the proof show (3)

Answer 5

• Observing the light produced from gases through a prism
• discovering a spectral pattern where colored lines were separated between dark bands (emission spectra)
• spectra where always the same for each gas

Question 6

How was this emission of discrete energy explained (proof for Rutherford’s second postulate)

Answer 6

Electron jumps between energy states (Excited state ➞ Ground state) release specific photons creating the same emission spectra pattern

Question 7

What is the equation to calculate energy of a photon

Answer 7

E = hf = hc/λ

Question 8

what is the Rydberg equation (the equation for the wavelength of a photon emitted from the de-excitation of electrons)

Answer 8

1/λ = R ( 1/n𝒻² - 1/nᵢ²)

Question 9

What were the limitations of the Bohr model (3)

Answer 9

• Could not explain the Zeeman effect (splitting of spectral line sin a magnetic field)
• Could not explain why electrons inhabited defined energy levels
• could not explain hyperfine spectral lines

Question 10

Who was the fourth person to changed the atom model

Answer 10

Louis de Broglie

Question 11

How did Louis de Broglie change Bohr’s atom model

Answer 11

• introduced the idea of wave-particle duality to explain why electrons had defined energy levels (shells)
• stating that each energy level corresponds to whole wavelengths, ( shell 1 = 1 wavelength, shell 2 = 2 wavelength etc)

Question 12

What was Louis de Broglie particle wave duality equation

Answer 12

λ = h/p

Question 13

What does each symbol in Louis de Broglie particle wave duality equation mean and what units are they measured in

Answer 13

λ = wavelength of the particle (metres (m))
h= Planck's constant (6.63 x 10 ⁻³⁴ Js 
p= momentum of the particle (kgms⁻¹)

Question 14

What experiments showed evidence for electrons as waves

Answer 14

• Davisson and Germer experiment

- Double slit experiment

Question 15

How did the double slit experiment show (2)

Answer 15

• By sending matter (ie electrons through double slits it will create a interference pattern as the quantum particles interact with each other
• But when measured the electrons would act like particles and only make two bands (with no interference

Question 16

How did the Davisson and Germer experiment work (2)

Answer 16

• Electrons were fired at nickel crystal

- causing the electron beam to diffract

Question 17

What is the mathematical equation (model) to show that whole integer value wavelengths can fit into an electron orbit (4)

Answer 17

2πr = nλ
=nh/p
= nh/mv
rearrange:
mvr= nh/2π

Question 18

Who was the 5th person to change the atom model

Answer 18

Erwin Schrodinger

Question 19

How did Erwin Schrodinger change the atom model (2)

Answer 19

• made a more complex particle wave duality equation for electrons
• displaying electrons by there probability of being in a certain area depicted as electron clouds
• explaining the hyperfine electron lines