1.3.1 - 1.3.3 Emission Spectrum

Question 1

Electromagnetic Spectrum

Answer 1

The electromagnetic spectrum refers to all the possible frequencies of electromagnetic radiation.

Question 2

Describe the relationship between colour, wavelength, frequency and energy across the electromagnetic spectrum.

Answer 2

Towards the red section of the spectrum, there is low energy, low frequency, and long wavelengths.

Towards the violet section of the spectrum, there is high energy, high frequency, and short wavelengths.

Question 3

Speed of Light Formula

Answer 3

Speed of Light (c) = wavelength (λ) × frequency (v or f)

∴ c= λv

Question 4

Frequency (v or f)

Answer 4

The number of wavelengths per unit of time.

Question 5

Wavelength (λ)

Answer 5

The distance between successive crests of a wave

Question 6

High Frequency

Answer 6

When wavelengths are closer together.

Question 7

Low Frequency

Answer 7

When wavelengths are further away from each other.

Question 8

Line Spectra

Answer 8

A spectrum only containing certain discrete wavelengths/frequencies/colours/energies of electromagnetic radiation.

Question 9

Line Emission Spectrum

Answer 9

A spectrum consisting of discrete wavelengths (or frequencies, colours, and energies) of electromagnetic radiation. It is produced when electrons in excited states transition to lower energy levels, emitting photons of specific energies.

Question 10

What is the relationship between the line emission and line absorption spectrum?

Answer 10

The colours absent in the absorption spectrum appear in the emission spectrum.

Question 11

Hydrogen Emission Spectrum

Answer 11

The set of discrete wavelengths of light (or frequencies, colours, and energies), emitted by photons, when electrons in hydrogen atoms transition from higher to lower energy levels. This produces distinct lines categorised into series- Lyman (UV (part of the spectrum)), Balmer (Visible Light (part of the spectrum)), and Paschen (Infra-red Light (part of the spectrum)) - dependent on energy difference/gap

E.g. electron absorbs energy excited it from n = 1 to n = 3

• if n = 3 –> n = 2: balmer series (photon of visible light released) - less energy released
• if n = 3 –> n = 1: lyman series (photon of UV) - more energy released.

Question 12

What does the spacing of lines in hydrogen emission spectrum represent/match?

Answer 12

The spacing of lines match the energy levels occupied by electrons in a hydrogen atom.

Question 13

Explain the process of photon emission.

Answer 13

1. Electron begins at ground state: lowest energy of an electron closest to the nucleus
2. The electron absorbs energy from a photon of light (e.g. source: heat)
3. Once energy is absorbed, the electron is in an excited state, jumping up to a higher energy level away from the nucleus
4. Due to electrostatic attraction, the electron must eventually return to the ground state. In this process, the electron emits excess energy as a photon of light (EM radiation) with a particular frequency - dependent on amount of energy initially absorbed.

Question 14

What is quantized energy levels?

Answer 14

Electrons in atoms are quantised meaning they can only exist in discrete energy levels.

Question 15

What is the flame test?

Answer 15

Heat is used as an energy source to excite the electrons. The colour of the photon of light is dependent on the amount of energy released during photon emission. As each element has unique quantised energy levels, all atoms of the same element release the same amount of energy, resulting in each element emitting a unique flame colour.

Question 16

Where are larger energy gaps (lower or higher energy levels)? What happens to energy, frequency, and wavelength within larger energy gaps?

Answer 16

Larger energy gaps are located between lower energy levels. This larger gap allows high transition energy and thus higher frequency and shorter wavelengths.

Question 16

What happens as the distance from the nucleus/centre of the atom increases?

Answer 16

As the distance from the centre increases, the distance between the energy levels decrease/ the energy levels converge, energy increases, frequency increases, and wavelengths get shorter.

Question 17

Where are smaller energy gaps (lower or higher energy levels)? What happens to energy, frequency, and wavelength within smaller energy gaps?

Answer 17

Smaller energy gaps are located between higher energy levels. This smaller gap results in low transition energy and thus lower frequency and longer wavelengths.

Question 18

Lyman Series

Answer 18

When an electron falls down to n = 1, producing UV light.
- Large energy gap: higher frequency, shorter wavelengths

Question 19

Balmer Series

Answer 19

When an electron falls down to n = 2, producing visible light.
- Medium energy gap: medium frequency, medium wavelengths

Question 20

Paschen Series

Answer 20

When an electron falls down to n = 3, producing infra-red light.
- Small energy gap: lower frequency, longer wavelengths

Question 21

Draw the hydrogen emission spectrum.

Answer 21

refer to notes

Question 22

How did the hydrogen spectrum allow Bohr to propose his model of electron configuration.

Answer 22

There were 2 key elements in both the hydrogen spectrum and Bohr’s proposal:

1. Electrons exist in discrete energy levels
   - electrons can only move between specific energy levels so the energy emitted is fixed, thus only certain wavelengths, corresponding to the energy, are represented by spectral lines are shown.
2. Energy levels converge as the distance from the nucleus increases
   - ionisation: at very high levels, the energy gaps become so small that the electron can escape completely