Chapter 3 - Electrons and energy levels [Complete]

Question 1

What is the equation linking energy and frequency?

Answer 1

Energy = planck’s constant x frequency

Question 2

What is the conversion between and electron volt and a joule?

Answer 2

1.6 x 10^-19 Joules (J) = 1 electron volt (eV)

Question 3

What is intensity in reference to electromagnetic radiation?

Answer 3

The energy transferred per unit time per unit area

Question 4

How could you increase the intensity of electromagnetic radiation?

Answer 4

Make the light source more powerful (e.g. 100W instead of 10W), make the photons each have a greater amount of energy (e.g. UV instead of visible), make the light incident on a smaller area (due to the inverse square law - when you half the distance the intensity increases x4)

Question 5

What is it called when all the electrons in an atom are in their base state?

Answer 5

The atom is in its ground state

Question 6

What is an absorption spectrum?

Answer 6

When light shines through a gas and lines are missing where energy frequencies have been taken by the gas for certain energy transitions

Question 7

What is a photon?

Answer 7

A particle representing a quantum of light/electromagnetic energy

Question 8

What is the equation for work done using electron volts?

Answer 8

Energy transferred in electron volts, W = potential difference in volts, V x electron charge, Q

Question 9

What is the inverse square law and where does apply in physics?

Answer 9

The inverse square law is when a quantity, in physics it is often intensity, is inversely proportional to the square of the distance from the source

Question 10

What could cause an electron to move up an energy level?

Answer 10

A collision with a photon

Question 11

What does quantised in the phrase ‘quantised energy levels’ mean?

Answer 11

That the energy levels are separate and have definite values

Question 12

Why are stairs analogical to the excitation of electrons?

Answer 12

As electrons can only be excited in certain phases, or steps - similar to how you cannot climb half a stair or part of a stair, either you move up or down by a step amount. The same goes with electrons - a certain amount of energy must absorbed and thus a certain distance moved each time an electron is excited or ionised

Question 13

What are the two ways in which an electron can gain enough energy to become excited or ionised?

Answer 13

By absorbing exactly the right amount of energy by either colliding with a free electron or from an incident photon

Question 14

What is ionisation?

Answer 14

When an electron within an atom gains enough energy to completely leave it, making the atom ionised and the electron free

Question 15

What is a diffraction grating?

Answer 15

A piece of transparent material ruled with very closely spaced lines which is used to see the diffraction of light

Question 16

What is an emission spectrum?

Answer 16

A bright spectrum seen when photons are emitted by electrons, for example when electrons fall from higher to lower energy levels within an atom

Question 17

What is an absorption spectrum?

Answer 17

A spectrum of dark lines seen on a coloured background produced when a gas absorbs photons. An example of this happening is when light comes from the Sun. When it is emitted, before it gets to the Earth, it passes through the outer layers of the Sun’s gases, causing parts of it to be absorbed by the atoms within them and thus dark lines, now known as ‘Fraunhofer lines’ on their absorption spectrum

Question 18

Why is it that despite electrons falling back to their original energy state, the black lines remain on absorption spectra?

Answer 18

As the photons emitted when they return back down the energy levels are emitted in all directions

Question 19

What is the ground state labelled as on a spectral line diagram?

Answer 19

n = 1

Question 20

When is the energy on a spectral line diagram 0?

Answer 20

When n = infinity, or the electron has fully ionised the atom

Question 21

What is fluorescence?

Answer 21

When a substance has the ability to absorb short wavelength radiation and emit it as longer wavelength radiation

Question 22

What is plasma?

Answer 22

A mixture of ions and electrons in a gas

Question 23

How does a fluorescent tube work?

Answer 23

At each end there is an anode or a cathode. When the light is switched on, a potential difference is applied across the tube, and free electrons flow across it. In the middle of the anode and cathode, however, is mercury gas. If the electrons collide inelastically with the gas, then the electrons within the mercury atoms may become excited. When they de-excite again, they release photons which strike the phosphors in the coating and are absorbed to be reemitted with a longer wavelength