U1-1 - Electromagnetic Radiation and Atomic Spectra

Question 1

Symbol for wavelength

Answer 1

λ (lambda)

Question 2

How do you convert wavelength from metres (m) to nanometres (nm)?

Answer 2

wavelength × 10⁹

Question 3

All electromagnetic waves travel at the same velocity in a vacuum − _____________________.

Answer 3

the speed of light (c).

Question 4

Arrange in order of increasing energy:

ultraviolet

infrared

visible

Answer 4

infrared, visible, ultraviolet

Question 5

Arrange in order of increasing wavelength:

ultraviolet

infrared

visible

Answer 5

ultraviolet, visible, infrared

Question 6

How many significant figures should an answer have?

Answer 6

One less or up to two more than expected

Expected = same as the number which has the lowest no. of sig. fig.

If in doubt, use 3 sig. fig.

Question 7

Multiple numbers are given in a question:

0.36
0.1
1.2

Which one determines the no. of significant figures in the answer?

Answer 7

0.1 (lowest no. of sig. fig.)

Question 8

What is meant by wave-particle duality?

Answer 8

Electromagnetic radiation can be considered both as a wave and as a stream of particles (photons).

Question 9

A photon carries quantised energy proportional to the frequency of radiation.

What does ‘quantised’ mean?

Answer 9

Can only have specific set values (not any random value).

Think height of each step on a staircase.

Question 10

What is h?

Answer 10

Planck’s constant

Question 11

What is L?

Answer 11

Avogadro’s constant

(no. of particles in 1 mole of a substance)

Question 12

‘Calculate the energy, in kJ mol⁻¹, associated with a wavelength of 671 nm.’

What conversion must be done before the calculation?

Answer 12

671 nm must be converted into m (671 × 10^–9)

This is to match speed of light units, m s^–1.

Question 13

When energy is transferred to atoms, electrons within the atoms may be _________________________.

Answer 13

promoted to higher energy levels

Question 14

An atom emits a _________ when an
excited electron moves from a higher energy level to a lower energy level.

Answer 14

photon

Question 15

An atom emits a photon when an
_________ electron moves from a higher energy level to a lower energy level.

Answer 15

excited

(increased energy)

Question 16

An atom emits a photon when an
excited electron moves from _______________________________.

Answer 16

a higher energy level to a lower energy level

Question 17

In emission spectroscopy, what is used to excite the electrons within atoms?

Answer 17

Heat

Question 18

Why do atomic spectra show multiple discrete lines?

Answer 18

Different electron transitions (between different energy levels).

Each transition produces a line.

Question 19

The concentration of an element within a sample is related to the intensity of light emitted or absorbed.

Higher intensity = ____________ concentration.

Answer 19

higher

Question 20

The energy of a photon emitted when an excited electron falls to a lower energy level is equal to __________________.

Answer 20

the energy gap between the two energy levels