Electromagnetic Radiation & Atomic Spectra

Question 1

Define ‘Wavelength’ and what units it is measured in.

Answer 1

Wavelength is the horizontal distance from one point of a wave to the same point of the next wave.

Wavelength is measured in metres unless radiation is in the visible part of the electromagnetic spectrum, where it is measured in nanometres (nm).

Question 2

Define ‘Frequency’ and what units it is measured in.

Answer 2

Frequency is the number of waves that pass a point in one second. It is measured in s^-1 or in Hertz.

Question 3

Describe ‘Velocity’ in electromagnetic radiation.

Answer 3

Velocity in electromagnetic radiation is constant and has a value of approximately 3 x 10^8 metres/second.

Question 4

What is the formula for velocity?

Answer 4

Velocity = frequency x wavelength

c=fλ

Question 5

What is the formula for wavelength?

Answer 5

Wavelength = velocity / frequency

λ=c/f

Question 6

What is the formula for frequency?

Answer 6

Frequency = velocity / wavelength
f = c / λ

Question 7

What are photons?

Answer 7

Photons are a stream of particles that carry quantised energy proportional to the frequency of radiation.

Question 8

What is the formula for the energy (in J) associated with a single photon?

Answer 8

Energy = Planck's constant x frequency
E = hf

OR

Energy = Planck's constant x velocity / wavelength
E = hc/λ

Question 9

What is the symbol and number for Planck’s constant?

Answer 9

Symbol - ‘h’

Number - 6.63 x 10^-34

Question 10

What is the symbol and number for Avogadro’s constant?

Answer 10

Symbol - ‘L’

Number - 6.02 x 10^23

Question 11

What is the formula for the energy (in J/mol) associated with one mole of photons?

Answer 11

Energy = Avogadro's constant x Planck's constant x frequency
E = Lhf

OR

Energy = Avogadro's constant x Planck's constant x velocity / wavelength
E = Lhc/λ

Question 12

What is the formula for the energy in kJ/mol?

Answer 12

Energy  = Avogadro's constant x Planck's constant x frequency / 1000
E = Lhf/1000

OR

Energy = Avogadro's constant x Planck's constant x velocity / (1000 x wavelength)
E = Lhc/1000λ

Question 13

What are the 2 types of Atomic Spectroscopy?

Answer 13

• Atomic Absorption Spectroscopy

- Atomic Emission Spectroscopy

Question 14

Describe atomic absorption spectroscopy.

Answer 14

When electromagnetic radiation is directed at an atomised sample, radiation is absorbed as electrons are promoted to higher energy levels.

An absorption spectrum is produced by measuring how the intensity of absorbed light varies with wavelength.

Question 15

Describe atomic emission spectroscopy.

Answer 15

In emission spectroscopy, high temperatures are used to excite the electrons within atoms. As the electrons drop to lower energy levels, photons are emitted.

An emission spectrum of a sample is produced by measuring the intensity of light emitted at different wavelengths.

Question 16

How is an atomic spectrum produced?

Answer 16

An atomic spectrum is produced by measuring the intensity of light absorbed or emitted at different wavelengths

Question 17

When doing energy calculations, how do you convert the wavelength in the visible spectrum into metres?

Answer 17

λ *10^-9