spectroscopy

Question 1

what is the speed of light?

Answer 1

3x10^8m/s

Question 2

what is the equation between speed of light, frequency and wavelength?

Answer 2

c = λf

Question 3

what does this equation show?

Answer 3

that wavelength is inversely proportional to frequency

Question 4

what is planck’s law? what do each of these represent?

Answer 4

E = hf
E = energy of a photon in Joules
h = 6.63x10^-34
f = frequency

Question 5

how are frequency and wavelength related, use the equation to explain this

Answer 5

f α 1/λ

Question 6

summarise how we use the electromagnetic spectrum for spectroscopy

Answer 6

spectroscopic excitations come about as a result of the movement of an electron(s) from lower to higher levels or vice versa. We can use these to work out the energy gaps between subshells and orbitals

Question 7

what does absorption spectroscopy measure?

Answer 7

light energy absorbed by an atom causing an electron to move from a lower energy level to a higher one

Question 8

why are the gaps between energy levels decreasing in absorption spectroscopy?

Answer 8

the energy differences is decreasing as frequency increases

Question 9

what does emission spectroscopy measure?

Answer 9

measure the light emitted when the excited electron falls back to lower energy levels

Question 10

why does an emission spectrum consist of a series of sharp lines?

Answer 10

because the energy levels are quantised (so only certain energy transitions are possible and certain frequencies are observed)

Question 11

define ‘convergence limit’

Answer 11

the point in the emission spectrum when the separate lines cannot be distinguished at n = ∞

Question 12

what happens at the convergence limit?

Answer 12

the nucleus has lost influence over the electron and therefore ionisation occurs

Question 13

how do you work out the ionisation energy from the convergence limit?

Answer 13

frequency at the convergence limit
E=hf

Question 14

how would you convert from J per atom to kJmol-3

Answer 14

energy J per atom x avogadros constant ÷1000

Question 15

how would you get from nm to m?

Answer 15

x10^-9

Question 16

how wouldyou get from nm to mm?

Answer 16

x10^-6

Question 17

nm to cm?

Answer 17

x10^-7

Question 18

what are the two different atomic emission spectrum of hydrogen?

Answer 18

The Lyman (UV) series and The Balmer (Visible Region) series

Question 19

what is the ionisation energy of hydrogen in the Lyman series?

Answer 19

difference of n=1 and n=∞

Question 20

Where do the electrons fall from in the Lyman series?

Answer 20

from higher levels to n=1 or ground state

Question 21

Where do the electrons fall from in the Balmer series?

Answer 21

from high energy levels to n=2

Question 22

Why do the lines show up in the mroe energetic UV part of the spectrum in the Lyman series?

Answer 22

n=1 is closest to the nucleus (lowest energy) so far more energy is released when it returns to n=1

Question 23

Why do we see the emitted energy as a line in the spectrum in the Balmer series?

Answer 23

they are in the visible spectrum

Question 24

In the Balmer series, where does the electron fall from when it emits a red line? Green line? Blue line? Purple line?

Answer 24

Red falls from n=3 to n=2
Green falls from n=4 to n=2
Blue falls from n=5 to n=2
Purple falls from n=6 to n=2

Question 25

Explain why hydrogen atoms emit only certain definite frequencies of visible light.

Answer 25

The electrons fall from higher energy levels to lower energy levels so the difference between the energy levels is quantised/fixed