Chapter 3 - Arrangement of Electrons in an Atom

Question 1

What happens to the continuous spectrum produced by a glass prism when the source of white light is replaced with light from a hydrogen discharge tube?

Answer 1

You only see a few colours with narrow lines and this spectrum is called an emission line spectrum

Question 2

What is a discharge tube?

Answer 2

A glass tube filled with gas at low pressure, with an electric current passed through it

Question 3

Spectrometer

Answer 3

Instrument used to carry out measurements on spectra

Question 4

Spectroscope

Answer 4

Instrument used to simply observe spectra

Question 5

Describe the experiment to carry out flame tests with various salts

Answer 5

1. Using a damp wooden splint/platinum wire, hold a sample of salt in the blue flame of the Bunsen
2. Repeat with the other salts
3. Each metal gives a characteristic colour
4. You can use the colours obtained to identify metals present in unknown compounds

Question 6

What colour does lithium turn in the flame test?

Answer 6

Crimson

Question 7

What colour does potassium turn in the flame test?

Answer 7

Lilac

Question 8

What colour does barium turn in the flame test?

Answer 8

Green

Question 9

What colour does copper turn in the flame test?

Answer 9

Blue-green

Question 10

What colour does strontium turn in the flame test?

Answer 10

Red

Question 11

What colour does sodium turn in the flame test?

Answer 11

Yellow

Question 12

Summarise Bohr’s Theory of electrons (12)

Answer 12

1. Electrons revolve around nucleus in fixed orbit
2. Each energy level has a fixed amount of energy
3. Energy levels are represented as n=1, n=2 etc
4. Once an electron remains in one orbit/energy level it neither gains nor loses energy
5. Atoms normally exist in their ground state
6. When an atom in ground state is provided with energy, a specific amount of this energy is absorbed and the electrons from lower to higher energy levels
7. Energy absorbed = difference in energy between ground and excited state
8. Electrons in ground state are unstable and soon fall down to lower energy level, and this excess energy is released in the form of a photon of light
9. Frequency of light emitted depends on the difference in energy between the two levels (E₂ - E₁ = hf)
10. Energy difference between levels is proportional to frequency of light emitted
11. Light of definite frequency appears as a line of particular colour on the emission line spectrum
12. Each element has a unique emission line spectrum

Question 13

Energy level

Answer 13

The fixed energy value that an electron in an atom may have

Question 14

Ground state

Answer 14

Where electrons of an atom occupy the lowest available energy levels

Question 15

Excited state

Answer 15

Where electrons of an atom occupy higher energy levels that those available in the ground state

Question 16

Why does each element have a different emission line spectrum?

Answer 16

Each element has a different number of electrons and its own arrangement of these electrons in energy levels (and depending on how much energy is supplied). As electrons fall different distances, different frequencies of light are given off

Question 17

What are the three series of light

Answer 17

Lymen series → invisible: found in ultraviolet radiation
Balmer series → Visible light
Paschen series → Invisible: infrared

Question 18

What is an atomic absorption spectrum?

Answer 18

Atoms can absorb light. If white light is passed through a gaseous sample of an element, we see that the light that emerges has certain wavelengths missing. This is called the atomic absorption spectrum

Question 19

Atomic absorption spectrometer

Answer 19

Instrument used in the analysis of water for heavy metals

Question 20

What does s, p, d and f stand for in terms of energy sublevels?

Answer 20

sharp
principal
diffuse
fundamental

Question 21

What did Louis de Broglie do?

Answer 21

Said you could detect the wave motion for an electron as it is such a small object

Question 22

Heisenburg Uncertainty Principal

Answer 22

States it is impossible to determine with perfect accuracy both the position and velocity of a particle at any given point in time

Question 23

What are the limitations to Bohr’s Theory (of electrons)?

Answer 23

○Didn’t explain the many lines on the emission line spectra of elements other than hydrogen
○Didn’t take into account that an electron has a wave motion, i.e. the electron can’t travel in a precise path at a precise distance from the nucleus
○In conflict with Heisenburg’s Uncertainty Principal as we can only refer to the probability of finding an electron in a region of space
○Didn’t take into account the presence of sublevels

Question 24

Orbital

Answer 24

Region in space within which there is a high probability of finding an electron

Question 25

Who used mathematical equations to work out the probability of finding an electron in any sublevel?

Answer 25

Schrodinger

Question 26

What shape is the s orbital?

Answer 26

spherical

Question 27

What shape is the p orbital?

Answer 27

dumbbell shape centres on the x, y and z axis

Question 28

Sublevel

Answer 28

Subdivision of the main energy levels and consists of one or more orbitals of the same energy