Emission Spectra

Question 1

How is Rutherford’s model flawed?

Answer 1

Electrons accelerate (circular orbit), giving off energy 
But if energy carried away, EP reduced, electron should move closed to nucleus… unstable 

Spectrum of EM would be continuous in theory

Question 2

Emission spectra of liquids/solids and gases

Answer 2

Liquids and solids produce CONTINUOUS spectra - electrons are shared between many atoms giving a huge range of possible frequencies.
Hotter = higher frequency limit emitted

Gas - line spectra due to excitation of INDIVIDUAL electrons which don’t interact with each other

Question 3

What is a spectroscope?

Answer 3

Device that breaks up visible light emitted from a source into a spectrum

Question 4

Absorption spectra

Answer 4

Gases can absorb specific frequencies when a continuous spectrum is shone through

Dark lines

Question 5

Why are there distinct spectral lines?

Answer 5

Photon passed through gas
Photons with the same energy as the energy gaps in the atoms are absorbed (e jumps up)

Atoms have specific energy levels, hence only specific wavelengths of light absorbed or emitted

Question 6

Describe the Bohr model of the atom

Answer 6

Only certain orbits are stable (stationary states)
Closest orbital radius is the “ground state”

Change in energy when an electron changes levels

Because the electron can only make certain jumps in its energy level, it can only emit photons of certain frequencies

Question 7

ΔE = hf

For energy levels

Answer 7

Difference in energy between two levels

hf = Ei - Ef

Question 8

Name the three series of energy jumps

Answer 8

Lyman - transitions between n=1 and higher orbits
UV

Balmer - n=2 and higher
Visible

Paschen - n=3 and higher
Infrared

PuBLic 321

Question 9

Rydberg equation

1/λ = R (1/S^2 - 1/L^2)

Answer 9

λ = wavelength of emitted photon

R = rydberg-ritz constant

S = series electron falls TO
L = series electron falls FROM
So that it’s positive

Paschen S=3, Balmer S=2, Lyman S=1
L=3+

Question 10

Define eV

Answer 10

Electron volt

1eV is the amount of energy involved in accelerating an electron through a potential difference of one volt

= 1.6 x 10^-19 J

Question 11

Define Electron potential energy

What is it for H ground state?

+ formula

Answer 11

The amount of energy it would take to ionise the electron

For an electron in H ground state n=1, the electron potential energy is -13.6eV
Negative as it is POTENTIAL energy

For H ONLY
E = -(hcR)/(n^2)

E = energy of emitted PHOTON 
c = speed of light 
h is plancks 
R is rydberg ritz 
n = energy level of hydrogen