Atomic Structure Flashcards
From Greek philosophers to Early 20th Century, how where the beliefs about atoms formulate and changed
- 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
What did Ernst Rutherford use experiments to work out the structure of the atom
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
What did Neils Bohr believe about the structure of an Atom
suggested that the energy of an electron in a particular orbit was quantised e.g. the hydrogen emission spectrum
Energy is defined as what for a free electron
Zero
All energies for bound electrons are
Negative
Ionisation energy is what
Where does the evidence for this come from
The energy to remove an electron from an atom
Calculated energy level agree exactly with those measured experimentally in the atomic spetrum of hydrogen
What is frequency in terms of waves (v)
Number of waves passing per second
How do you work out frequency of a wave
v = c / λ
Where c = 3.00 x 10^8 m-s = velocity of light
λ = wavelength
What is the relationship between wavelength and frequency
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
- Planck - radiation is quantised, i.e. consists of a stream of PARTICLES
- Einstein - these particles (quanta) are called PHOTONS
- Planck - the energy of a quantum (photon) is given by the equation: E = hν
(where h = Planck’s constant, 6.63 × 10-34 Js)
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?
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
What is the photoelectric effect
the ejection of electrons from a material on irradiation of light
What is the photoelectric effect
the ejection of electrons from a material on irradiation of light
Photons carry ….
the energy from planck’s law with a current flowing above a minimum frequency
Therefore the evidence from the photoelectric effect and flame suggest which property about radiation
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.
What is the ‘de Broglie Relationship’
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)
What does the de Broglie Relationship explain
the so called ‘wave-particle duality’
The proposal made by de Broglie paved the way for the development of which piece of technology
The electron microscope
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
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
How is momentum worked out
p (momentum) = Mass x Velocity
What is the Heisenberg Uncertainity Principle
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
What is the Heisenberg Uncertainity Principle
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
What does the Heisenberg uncertainity principle tell us
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.
How does the size of an object relate to the heisenberg uncertainity principle
The Heisenberg Uncertainty Principle applies to all matter but is only significant for very small objects (size of Planck’s constant).
How would you rearrange the heisenburg equation to work out Δx
(m x Δv) = Δp
