Atomic Structure

Question 1

From Greek philosophers to Early 20th Century, how where the beliefs about atoms formulate and changed

Answer 1

• Greek philosophers - pure theory
• Early 19th century - John Dalton - Atoms combine to form compounds
• Early 20th century - Rutherford – scattering of alpha particles (He2+ ions) by nuclei in a gold foil Atomic structure of hydrogen (simplest): Atomic radius (≈50 pm) Nucleus - nearly all the mass - radius ≈10-3 pm Electron - only 1/1850 of mass

Question 2

What did Ernst Rutherford use experiments to work out the structure of the atom

Answer 2

tried to use classical mechanics (Newton) to explain behaviour of atoms.
This approach failed as the orbit of the electron would gradually decay and collide with the nucleus

Question 3

What did Neils Bohr believe about the structure of an Atom

Answer 3

suggested that the energy of an electron in a particular orbit was quantised e.g. the hydrogen emission spectrum

Question 4

Energy is defined as what for a free electron

Answer 4

Zero

Question 5

All energies for bound electrons are

Answer 5

Negative

Question 6

Ionisation energy is what
Where does the evidence for this come from

Answer 6

The energy to remove an electron from an atom
Calculated energy level agree exactly with those measured experimentally in the atomic spetrum of hydrogen

Question 7

What is frequency in terms of waves (v)

Answer 7

Number of waves passing per second

Question 8

How do you work out frequency of a wave

Answer 8

v = c / λ
Where c = 3.00 x 10^8 m-s = velocity of light
λ = wavelength

Question 9

What is the relationship between wavelength and frequency

Answer 9

Question 10

In the late 19th century the were some problems - several properties of radiation were discovered which could not be explained by solely wave behaviour.
These problems were explained by Max Planck and Albert Einstein.
How

Answer 10

1. Planck - radiation is quantised, i.e. consists of a stream of PARTICLES
2. Einstein - these particles (quanta) are called PHOTONS
3. Planck - the energy of a quantum (photon) is given by the equation: E = hν
   (where h = Planck’s constant, 6.63 × 10-34 Js)

Question 11

Why do metal ions in the vapour phase emit light?
Why does the colour vary with the metal ion?
e.g. Lithium red, Sodium yellow, Potassium lilac, Barium green
How does this reflect the atomic structure?

Answer 11

The metal will absorb heat from the flame causing electrons to be promoted to higher energy levels, however they immediately return to ground state releasing that energy in the form of radiation in the visible light spectum
The spacing between energy levels due to differences in atmoic structure in an atom determines the sizes of the transitions that occur, and thus the energy and wavelengths of the collection of photons emitted

Question 12

What is the photoelectric effect

Answer 12

the ejection of electrons from a material on irradiation of light

Question 12

What is the photoelectric effect

Answer 12

the ejection of electrons from a material on irradiation of light

Question 13

Photons carry ….

Answer 13

the energy from planck’s law with a current flowing above a minimum frequency

Question 14

Therefore the evidence from the photoelectric effect and flame suggest which property about radiation

Answer 14

There is therefore strong evidence that radiation has the properties of both waves and particles!!
All early experiments on atoms, nuclei and electrons assumed that they were particles.
No theory could be found to explain their properties.

Question 15

What is the ‘de Broglie Relationship’

Answer 15

De Broglie pointed out that the energies calculated for a wave and for a partucle must be equal - for any object which was behaving as both
λ = h/p
Where λ = wavelength of wave
p = momentum of particle (i.e. mass x velocity)
h = Planck’s constant (6.63 x 10^-34)

Question 16

What does the de Broglie Relationship explain

Answer 16

the so called ‘wave-particle duality’

Question 17

The proposal made by de Broglie paved the way for the development of which piece of technology

Answer 17

The electron microscope

Question 18

Early ideas of suggested electrons in an atom like planets going around the sun - path was a well-defined orbit
However now we know that an electron has wave-like properties, with a wavelength ( λ) the same order of magnitide as the size of an atom, what does this mean

Answer 18

such precision to find the position off an electron is impossible
All we can do is to determine the probability that an electron is in a certain place
This is done through te Heisenberg uncertainity principle

Question 19

How is momentum worked out

Answer 19

p (momentum) = Mass x Velocity

Question 20

What is the Heisenberg Uncertainity Principle

Answer 20

Where the position of the elctron in space is defined by 3 coordinated: x, y and z
Where P (momentum) is parallel to each axis: px, py and pz
The right side of the equation is contant

Question 21

What is the Heisenberg Uncertainity Principle

Answer 21

Where the position of the elctron in space is defined by 3 coordinated: x, y and z
Where P (momentum) is parallel to each axis: px, py and pz
The right side of the equation is contant

Question 22

What does the Heisenberg uncertainity principle tell us

Answer 22

The more accurately we know the position of an electron, the less accurately we can know its momentum vice veras
This is not due to our experimental inadequacy, it is an inherent property of matter.

Question 23

How does the size of an object relate to the heisenberg uncertainity principle

Answer 23

The Heisenberg Uncertainty Principle applies to all matter but is only significant for very small objects (size of Planck’s constant).

Question 24

How would you rearrange the heisenburg equation to work out Δx

Answer 24

(m x Δv) = Δp