FIC May 23 exam Flashcards
Identify how responses to electric fields differ between alpha, beta and Gamma radiation ?
Alpha - Helium Nucleus - 2+ charge - attracted to -ve plate - small deflection
Beta - High speed electrons - light - attracted to +ve plate - large deflection
Gamma radiation - high-energy radiation similar to X-rays - no deflection
Which is the incorrect answer ?
(A) An alpha particle shows a small deflection towards the negative plate of an electric field
(B) The charged particles detected in cathode rays by JJ Thomson were electrons
(C) Milliken determined the charge on the electron by observing the rate of fall of charged oil droplets
(D) A gamma ray splits and shows an equal deflection toward the negative and positive plate of an electric field.
(D) A gamma ray is not charged
What is the order of the electromagnetic spectrum in terms of decreasing wavelength and increasing frequency ?
Gamma rays - X-rays - UV - Visible - IR - Microwaves - Radio
Raging Martians invaded Venus using X-ray guns
Calculate the energy (in J) of light with a frequency of 9 x 10*15 s-1
5.96 x 10*18
E = hv
Calculate the energy of a wave of wavelength 520 nm
3.82 x 10*-19J
E = hc / wavelength
Describe the visible changes when T increases on black body objects
As T increases glows red then Blue / White
How is wavelength affected by changes in T in black body radiation ?
Wavelength (red / lower T) > Wavelength (blue / higher T)
As T increases the peak in intensity of radiation will shift to a shorter wavelength
Outline the term ‘Ultraviolet catastrophe’
Classical physics suggests a black body should emit an infinite amount of energy as the frequency of the radiation approaches infinity. However this would breakdown the laws of physics.
Disproved because experiments showed energy did not increase indefinitely, reached maximum and decreased at higher frequencies.
Outline the term ‘Ultraviolet catastrophe’
Classical physics suggests a black body should emit an infinite amount of energy as the frequency of the radiation approaches infinity. However this would breakdown the laws of physics.
Disproved because experiments showed energy did not increase indefinitely, reached maximum and decreased at higher frequencies.
What is the relationship between energy and wavelength
Energy is inversely proportional to wavelength
Suppose that yellow visible light can be used to eject electrons from a certain metal surface. What would happen if ultraviolet light was used instead and why ?
UV Light has a shorter wavelength, higher frequency and therefor higher energy - so the electron would be ejected with a greater kinetic energy than those ejected by the yellow light.
Explain the difference between absorption and emission
spectra
Émission spectra
- electron drops from higher energy level to lower
- photon of energy is emitted
- detect wavelength of this line
Absorption spectra
- photon of energy is absorbed.
- Electron is excited from lower energy level to higher.
- Detect wavelength of this line.
Explain how Bohr explained line spectra
Electron in an atom can only occupy certain circular orbits (corresponding to certain energies and specific radius)
How do you calculate energy using plank’s constant and frequency
E = hv
Identify the key features of the Bohr model which hold true.
Electrons exist only in discrete energy levels - described by quantum numbers
Energy is involved in moving an electron from one state to another.
As the electron in a hydrogen atom jumps from n = 3 orbit to the n = 7 orbit, does it absorb or emit energy?
It absorbs energy.
The electron moves from a lower-energy to a higher-energy state (absorption).
How do you calculate wavelength using planck constant, mass and frequency ?
Wavelength = Planck constant / mass * frequency
Does a moving tennis ball generate matter waves?
If so, can we observe them?
Yes!! The mass of the electron is 9.109 x 10-31 kg is much smaller than the mass of a tennis ball 0.05kg. Therefore, the wavelength associated with a tennis ball is too small to observe.
Calculate the uncertainty in the position of an electron moving with an uncertainty in the velocity of 5 ms-1 ?
Electron with a mass of me = 9.109 x 10*-31
1.16 x 10*-5
Delta x * Delta P = h / 4pi
Delta p = Mass * uncertainty in the velocity
Delta p = (9.109 x 10*-31) x 5
Delta x = (h / 4pi) / Delta P
What does wave-function show ?
Wave-function gives a probability density map of where an electron has a certain statistical likelihood of being at any given instant in time.
What is and what are the allowed values of the principle quantum number (n) ?
1, 2, 3, 4… (integers)
Shows the spatial orientation
What type of orbital does the azimuthal quantum number (l) correlate too ?
Value of l (type of orbital)
0(s) 1(p) 2(d) 3(f)
What is and what are the allowed values of the Azimuthal quantum number (l) ?
Defines the shape and energy of the orbital.
Allowed values range from 0 to n-1.
What is and what are the allowed values of the Magnetic quantum number (ml) ?
Described the three-dimensional orientation of the orbital.
Values are integers ranging from -l to l
What are the allowed values of the spin quantum number (ms) ?
+ or = 1/2.
Sketch a Radial wavefunction graph for a 1s orbital
Check answer
Sketch a radial wavefunction graph for a 2s orbital
Check answer
Sketch the radial wavefunction graphs for 3s, 3p and 3d orbitals
Check answer
What is the equation for No. of radial nodes
n - l - 1
How does the n value correlate to the distance between energy levels ?
Energy levels become closer together as n value increases
How does number of electrons affect repulsion ?
As the number of e-s increases, so does the repulsion between them.
In quantum mechanics, what does it mean for subshells to be ‘degenerate’ ?
An energy level is degenerate if it corresponds to two or more different measurable states of a quantum system.
In quantum mechanics, what does it mean for subshells to be ‘degenerate’ ?
An energy level is degenerate if it corresponds to two or more different measurable states of a quantum system.
Outline Pauli’s exclusion principle
No two fermions (particles with half integer spin) can occupy the same quantum state simultaneously. Which is why the spin quantum numbers of a quantum state must be +1/2 and -1/2
Outline the Aufbau Principle
Electrons in atoms build up from the lowest energy levels.
Order of filling up orbitals - 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p
Exceptions to the rule due to extra stability associated with half-filled and filled sets of d-orbitals which can occur since the 4s and 3d orbitals are very close in energy.
Outline Hunds rule
For degenerate orbitals (ie p or d/0/ the lowest energy is attained when the number of electrons with the same spin is maximised.
Briefly describe the the components of an electrochemical cell
Comprised of two half cells, a electrode in contact with a redox solution.
Define electrode potential
Energy when the redox states within the redox couple at equilibrium.
What are voltaic cells ?
Two connected half cells also known as a battery. E released in redox reaction may be used to perform electrical work.
Define and outline the equation for electromotive force (emf)
Joining two electrodes to form a cell creates a potential difference between them called the electromotive force. At equilibrium the emf is the difference between the two electrode potentials.
emf = E(+) - E(-)
emf sometimes written as Delta E
Calculate emf for this daniel cell
Zn I Zn2+ (aq) I I Cu2+(aq) I Cu
-0.76v 0.34v
0.34v - (-0.76 volts) = 1.10 volts
Define Gibbs function (delta G) ?
Measure of useful work done in a chemical reaction occurring in the cell which may be equated with the electrical output of the cell.
What is the equation for Gibbs free energy ?
Delta G = Number of electrons in redox equation x Faraday constant (charge of 1 mole of electrons) x electromotive force
Define radial distribution function
RDF = Probability that electron lies in a spherical cell of radius, r, thickness dr - useful to find most probable distance of finding an electron from the nucleus.
What types of bonds are contained within single and multiple bonds ?
In single bonds the bonds are always sigma bonds.
In multiple bonds (double, triple etc) one bond is sigma the rest are pi.
How are sigma bonds characterised ?
Head to head overlap
Shared electron density with internuclear axis.
How are Pi bonds characterised ?
Side to side overlap
Electron density above and below the internuclear axis.
What is the difference between in phase vs out of phase ?
In phase refers to constructive overlap of atomic orbitals. Results in molecular orbital with lower energy and greater stability than the original atomic orbitals.
Out of phase refers to the destructive overlap of atomic orbitals. Results in molecular orbital with higher energy and lower stability than the original atomic orbitals.
What happens as overlap of orbitals increases ?
As overlap of orbitals increases
- bonding MO e lowered (stabilised)
- Anti-bonding MO e raised (destabilised) more compared to the atomic orbitals from which they are formed.
What characteristics do atomic orbitals need to have for significant overlap to occur ?
- Similar size
- Similar energies
- Same symmetry
What is the calculation for bond order ?
Bond order = 1/2 ((no. of bonding e-)-(no. of anti-bonding e-))
What does ‘end on’ overlap of p orbitals form ?
End on overlap forms sigma and sigma* Molecular orbitals.
