Unit 4

Unit 4-1 ð Concept 1 ð explaining how the discovery of cathode rays

contributed to the development of atomic models

Cathode rays where discovered as a result of experiments being done on the discharge of electricity through rarefied gases. It was observed that something being emitted by the cathode caused the gas to glow at the far end of the tube. This something was determined to be deflected by both electric and magnetic fields. J.J. Thomson from these experiments determined that this cathode ray was a very small negatively charged particle and from this determined that cathode rays (electrons) were constituents of the atom and not atoms as others believed.

Unit 4-1 ð Concept 2 ð explaining Thomsonâs experiment and the

significance of the results

The significance of Thomson's experiment lead to a measurement of the charge to mass ratio of the electron as well it gave him support for his theory that the electron was a constituent of an atom.

Unit 4-1 ð Concept 3ð deriving the relationship q/m = v / Br , using circular

motion and charged particles in electric and magnetic

field concepts

When an object travels in a circle a centripetal force is needed. In this case, the force is from the magnetic field. The velocity

Unit 4-1 ð Concept 4ð explaining Millikanâs experiment and its significance relative to charge quantization

Millikan used an electric field to suspend charged oil droplets in-order to determine the charge on the droplets. He them found that the smallest difference in charge between the droplets and determined this to be the charge on a single electron. By determining that an electron had a specific charge Millikan determined charge came in fix amounts or was quantized rather then being continuous.

Unit 4-1 ð Concept 5ð relating the electronvolt, as a unit of energy, to the

joule.

The electronvolt (eV) is a none base 10 unit of energy with a conversion factor of 1.6 x 10^-19J / eV

Unit 4-2 ð Concept 1ð explaining the necessity for Planck to introduce the quantum of energy concept to explain blackbody radiation

Planck needed to introduce the quantum energy idea n-order to explain the blackbody radiation curves. To obtain an agreement with theory and experimental curves Planck assumed that the energy of an oscillator could only have discrete values or fixed quantities. He derived the follow formula o explain these blackbody radiation curves

Unit 4-2 ð Concept 2 ð defining the photon as a quantum of electromagnetic

radiation

It was discovered later the "n" in Planck's equation represented the number of packages (fix quantity) of light given the name photon.

Unit 4-2 ð Concept 3 ð describing how Hertz discovered the photoelectric effect while investigating electromagnetic waves

Unit 4-2 ð Concept 4 ð explaining the photoelectric effect in terms of the intensity and wavelength of the incident light and surface material

The energy of the photoelectron increases with a an increase in the frequency (decrease in wavelength) of light. An increase in the intensity of light increases (number of photons) causes an increase in the photoelectric current.

Unit 4-2 ð Concept 5 ð assessing the assumptions made by Einstein in

explaining the photoelectric effect

Einstein assumed that the light came in bundles he called photons and that each photon would pass it's energy to each electron and the energy of the photon came from Planck's equation E=hf

Unit 4-2 ð Concept 6 ð defining threshold frequency as the minimum frequency giving rise to the photoelectric effect; and work function as the energy binding an electron to a photoelectric surface

Self explanatory

Unit 4-2 ð Concept 7 ð explaining the relationship between the kinetic energy

of a photoelectron and stopping voltage

The kinetic energy of the photoelectron was determined experimentally by placing a voltage to stop the photoelectric circuit. The E_k = V_stopq

Unit 4-2 ð Concept 8 ð using Einsteinâs equation, quantitatively, to describe

photoelectric emission

The incident photon energy "hf" becomes kinetic energy of the photoelectron "Ekmax" and the energy to be released from the metal or work function "W"

Unit 4-2 ð Concept 9 ð describing the photoelectric effect as a phenomenon that supports the notion of the wave÷particle duality of electromagnetic radiation

Light was believed to be a wave. Einstein's explanation of the photoelectric effect using a particle model of light gave rise to a wave-particle model of light because both models are needed to explain all the phenomenon light waves exhibit.

Unit 4-2 ð Concept 10 ð explaining X-ray production as an inverse photoelectric effect, and predicting, quantitatively, the short wavelength limit of X-rays produced, given appropriate data

In the photoelectric effect, photons release energy to photoelectrons. The opposite occurs with x-rays. High-energy electrons collide with a metal target to release a photon during the collision or slowing of the electron. The kinetic energy of the electron is released as a high-energy photon.

Unit 4-2 ð Concept 11 ð explaining, qualitatively, the Compton effect and the de Broglie hypothesis applying the laws of mechanics, conservation of momentum and energy, to photons, as another example of wave÷particle duality.

Compton showed that photons had momentum p = h/ l a particle property. deBroglie by combining photon momentum and momentum of matter derived a formula which suggested matter traveled as waves. This was latter proven correct. This strengthened the wave-particle duality idea, if matter could have wave properties, a wave could have matter properties.

Unit 4-3 ð Concept 1ð using the isotope notation to describe and identify

common nuclear isotopes, and determine the number of each nucleon of an atom

^A_ZX

X = the symbol of the element

A = the mass number of the element (the number of neutrons and protons or number of nucleons)

Z = the number of protons

Unit 4-3 ð Concept 2ð describing the nature and behavior of alpha, beta and

gamma radiation

Alpha decay is a high-speed ionized helium particle. This type of radiation has very little penetrating power.

Beta decay is a high-energy electron. Beta particles have a higher ability to penetrate.

Gamma rays are high-energy photons of light which are a result of the nucleus jumping to a lower energy state. Gamma has the highest penetrating power of the three.

Unit 4-3 ð Concept 3ð writing nuclear equations for alpha and beta decay

Alpha decay ²²⁷ ₉₀^Th ½ ²²³₈₈Ra + ⁴₂He

Beta decay ¹⁴₆C ½ ¹⁴₇N + ⁰_-1B

Unit 4-3 ð Concept 4ð performing simple, nonlogarithmic, half-life calculations

Half life is a statistical probability. It is the time is takes one half of a radioactive sample to decay. When asked to find time or a 1/2 life n will be given as whole number.

Unit 4-3 ð Concept 5ð predicting the particles emitted by a nucleus from the examination of representative transmutation equations

When an element is bombarded by another particle or element the result may yield many different elements but all transmutations must conserve the number of nucleons as well as the charge of the system

¹⁴₇N + ⁴₂He ½ ¹⁷₈O + ¹₁H note the on both sides there are 18 nucleons and 9 protons

Unit 4-3 ð Concept 6ð explaining, qualitatively, how radiation is absorbed by matter, and compare and contrast the biological effects of different types of radiation

Unit 4-3 ð Concept 7ð comparing and contrasting the characteristics of fission and fusion reactions

Fission reactions split large atoms into smaller ones while fusion reactions fuse two smaller atoms together to make one larger atom.

Unit 4-3 ð Concept 8ð explaining, qualitatively, the importance of Einsteinâs

concept of mass÷energy equivalence

Einstein's equation states E=mc² _.This means that mass can be converted to energy. It also means that the conversion of only very small amounts of matter are needed to create vast amounts of energy.

Unit 4-3 ð Concept 9ð relating, qualitatively, the mass defect of the nucleus to the energy released in nuclear reactions.

In radioactive decay or in nuclear fission or fusion the energy released comes from what is known as the mass defect. The mass defect is the mass difference between the mass of the reactants and that of the products.

Unit 4-4 ð Concept 1 ð explaining, qualitatively, the significance of the results of Rutherfordâs scattering experiment in terms of the nature and role of the nucleons; and the size and mass of the nucleus and the atom, which lead to the proposal of a planetary model of the atom

In Rutherford's gold foil scattering experiment he found that alpha particles were scatter much more that a solid model of the atom would predict. He concluded that almost all of the mass and all the positive charge of an element is located in the centre of a atom or nucleus and the negative charge was located with the electrons orbiting the nucleus like planets orbit the sun .

Unit 4-4 ð Concept 2 ð explaining why Maxwellâs theory of electromagnetism predicts the failure of a planetary model of the atom

Maxwell's theory states that an accelerating charge will produce an EM wave and a object traveling in a circle is under going centripetal acceleration. Therefore the electrons should be continually emitting EM waves and as they do so loose energy and slow down eventually collapsing into the nucleus. This is not observed.

Unit 4-4 ð Concept 3 ð describing why each element has a unique line spectrum, and comparing and contrasting the characteristics of continuous and line spectra

A specific colour of light will be emitted when an electron jumps from one energy state to another. Each element has a different line spectrum because each element has a different number and arrangement of electron energy levels.

Unit 4-4 ð Concept 4 ð explaining, qualitatively, the conditions necessary to produce line emission and line absorption spectra

To produce a line spectrum a gas must be heated. This is often done by bombarding the gas with high energy electrons. An absorption spectrum is produced by passing white light through a cool gas. (note: the light from both needs to be viewed through a spectroscope.

Unit 4-4 ð Concept 5 ð explaining the quantum implications of the line absorption and the line emission spectra, and determining any variable in the Balmer equation 1/ l = R_H (1/n²_f - 1/n²_I)

In the balmer equation n can only be a whole number or fix quantity. This means that the energy states are quantized.

Unit 4-4 ð Concept 6ð explaining Bohrâs concept of "stationary states" and their relationship to line spectra of atoms; and using the frequency/wavelength of an emitted photon to determine the energy difference between states

Bohr fixed Rutherford's planetary model of the atom by stating that electron existed in fix energy states and only emit photons when they jump down energy states. The difference in energy between states will become the energy of the emitted photon.

E_initial - E_final = hf

Unit 4-4 ð Concept 7 ð explaining the relationship between hydrogenâs absorption spectrum and its energy levels

all elements including Hydrogen absorb only photons with the same energy as the energy difference between energy states.

Unit 4-4 ð Concept 8 ð describing how the Bohr atom can be used to predict

the ionization energy of hydrogen, and to calculate the allowed radii of the hydrogen atom

The energy of any electron energy level can be calculated using

The radius of the electron energy level can be calculated using

Unit 4-4 ð Concept 9 ð describing how the Rutherford÷Bohr model has been further refined, by applying quantum concepts to a purely mathematical model based on probability and waves

The Bohr and Rutherford models have been replaced by the electron cloud model

Unit 4-4 ð Concept 10 ð comparing and contrasting, qualitatively, the Rutherford, the Bohr and the quantum model of the atom.

The Bohr and Rutherford models have exact numbers for the position of the electron in any energy state while the cloud model takes about the probability of finding the electron.