2.5

Question 1

Describe the atomic structure in the Bohr model of the atom

Answer 1

The Bohr model describe the structure of the atom as having a central, positively charged nucleus with oribiting electrons at fixed distances from the nucleus in ‘energy levels’

Question 2

Describe some of the features of the Bohr’s model

Answer 2

• electrons are in circular oribits around the nucleus
• electron oribits correspond to energy levels
• electrons in the lowest energy orbit are said to be in the ground state
• electrons can gain energy to move to higher energy levels (excited states) or lose energy to drop down energy levels

Question 3

What is the ground state?

Answer 3

The lowest energy level

Question 4

What is an excited state?

Answer 4

When an electron gains energy and moves up an energy level

Question 5

What is ionisation?

Answer 5

When an electron gains enough energy to be completely removed from the atom or when an atom gains an electron.

Question 6

What happens when an electron in an excited state returns to a lower energy level?

Answer 6

When an electron from an excited state return to a lower energy level, energy is released. This energy is released as a photon, and the amount of energy lost is equal to the differnece between the energy levels the electron moves between.

Question 7

How do you calculate the energy of a photon emitted by an atom?

Answer 7

Calculate the difference in energy between the energy levels:
E2 - E1

Calculate frequency using: E = hf

Question 8

Why do emission spectra have multiple line of different wavelengths?

Answer 8

As there are multiple energy levels, there are multiple different electron transitions that can occur. Each possible electron transition between energy levels that can occur produces a different photon with a different frequency (and thus wavelength). This causes there to be multiple lines on line spectra.

Question 9

How can line spectra be used to identify elements?

Answer 9

Elements have different numbers of electrons and energy levels, meaning that there are different possibilities of electron transtitions between energy levels. This gives each element a unique emission spectrum.

Question 10

How can continuous emission spectra be produced?

Answer 10

Continuous spectra are produced from electrons being shared between a large number of atoms, creating a large range of possible transitions between energy levels.

Question 11

How are absorption spectra produced?

Answer 11

When photons pass through a gap, the photons with the same energy as the gaps between energy levels are absorbed, creating an absorption spectrum.

Question 12

What are Fraunhofer lines?

Answer 12

Lines in the absorption spectrum

Question 13

How can absorption spectra be used to determine the elemental composition of the Sun?

Answer 13

The Fraunhofer lines in the light spectrum from the Sun coincide for specific elements, allowing us to deteremine its elemental composition.

Question 14

What happens when an electron drops from a higher energy level?

Answer 14

a photon is emitted. Only photons with energies exactly matched to the difference between two energy levels can be emitted

Question 15

When does a electron move to a higher energy level?

Answer 15

when it absorbs the energy of a photon. Only photons with energies exactly matched to the difference between two energy levels can be absorbed.

Question 16

What is electron transtition?

Answer 16

the movement of an electron from one energy level to another. Electrons can move between energy levels by emitting or absorbing photons of electromagnetic radiation.

Question 17

How can the light from a star be analysed?

Answer 17

using a prism or spectroscope

Question 18

What is continuous spectra?

Answer 18

consists of a complete/continuous spectrum with certain colours missing which appear as black lines in the spectrum

Question 19

What is line spectra?

Answer 19

consists of lines of light of distinct colours rather than a continuous spectrum

Question 20

What is absorption spectra?

Answer 20

formed when light with a continuous spectrum passes through a low-pressure gas

Question 21

What is irradiance?

Answer 21

The power per unit area incident on a surface.

Question 22

What is the equation for irradiance?

Answer 22

I = P/A

Question 23

What is the relationship between irradiance and distance?

Answer 23

As the distance of a light source from a surface increases, the irradiance decreases. Therefore, this is an inversely proportional relationship.

Question 24

Give an equation to show the relationship between distance and irradiance

Answer 24

I = k/d^2

Question 25

Describe an experiment to show the inverse square law of irradiance

Answer 25

1. On a dark surface in a darkened room, set up a lamp and a light sensor.
2. Measure the ambient light in the room by switching off the lamp and rcording the light levels on the light sensor.
3. With a ruler to record distance and measure the light intensity at avrious distances from the source to the centre of the lamp by moving the light sensor.
4. Plot the irradiance values against distance on a graph, using the readings on the light sensor as irradiance