Last modified on 4 April 2015, at 07:15

IB Physics/Atomic and Nuclear Physics

7.1 Atoms and their constituentsEdit

Atomic structureEdit

7.1.1 Describe a model of the atom that features a small nucleus surrounded by electrons.Edit

  • The atom is spherical in shape composed of a small and dense nucleus.
  • The nucleus is composed of protons (that have a positive charge) and neutrons (that have a neutral charge).
  • The nucleus is orbited by "shells" of electrons.
  • The electrostatic attraction between the electrons and the nucleus keep the atom together.

7.1.2 Outline the evidence that supports a nuclear model of the atom.Edit

The Geiger-Marsden experiment supports the current nuclear model of the atom. The alpha particle scattering experiment (by Rutherford/Geiger+Marsden) involved firing alpha particles at a sheet of very thin gold foil, and detecting where they went (with a screen). The results of the experiment were that the majority of alpha particles passed straight through. Of those which were deflected, many were deflected through very large angles, and even straight back at the source. This result suggested that atoms consisted mostly of empty space, with a small nucleus of high positive charge.

Results of Geiger-Marsden experiment Explanation of results
Most particles passed through the gold foil The atom is composed mostly of space
A small percentage of the particles deflected at 0º-90º The gold nucleus is positive. Alpha particles are repelled by the nucleus, causing its path to deflect at an angle.
A small percentage of the particles "bounced" back at an angle larger than 90º The alpha particle collided with the gold nucleus.

7.1.3 Outline one limitation of the simple model of the nuclear atomEdit

Firstly, the simple model of the nuclear atom is that there is a small nucleus surrounded by orbiting electrons (there are no electron shells).

Rutherford's model was that around the small, highly charged nucleus, electrons orbited like planets around the sun. This created many more questions. Why didn't the electrons emit radiation and lose energy? How would they be kept in a constant orbit? Hence, the limitation of the simple model would be that the atom would decay quickly, as electrons would spiral into the nucleus.

7.1.4 Outline evidence for the existence of atomic energy levelsEdit

Elements emit light when given enough energy. This light can be analysed and each element has its own spectra. This is because elements do not provide a continuous spectrum of light.

Emission Spectra and absorption spectraEdit

Line spectra is produced when the element radiates light. This spectra corresponds to wavelengths of the same energy level jump, hence, different elements have different spectra. Elements can only occupy given energy levels and is said to be quantised. When the electron moves between the energy levels, it emits or absorbs energy.This energy is emitted or absorbed as "packets" of light called photons. When the electron emits energy in an emission spectra, it gives it off as a wavelength of light of a particular colour. When the electron absorbs energy in an absorption spectra, the light of the particular wavelength is shown as a black line.


Light is not simply a continuous wave but is emitted as "packets" of light called photons. Only photons of the same energy as the energy in the electron jump will be emitted.



E= photon energy (J)

h= Planck's constant (6.63*10^{-24} Js)

f= Frequency of light (Hz)

Nuclear structureEdit

7.1.5 Explain the terms nuclide, isotope and nucleon.Edit

Word Definition
Nuclide A particular species of atom which contains a specific number of protons and neutrons.
Isotope Atoms that contain the same number of protons but different number of neutrons
Nucleon The protons and neutrons in the nucleus

7.1.6 Define nucleon number (A), proton number (Z) and neutron number (N)Edit

Word Definition
Nucleon number The number of nucleons (protons and neutrons)
Atomic/proton number The number of protons in the nucleus
Neutron number The number of neutrons in an atom


7.1.7 Describe the interactions in a nucleusEdit

There are forces that exist within the nucleus of the atom.

Force (interaction) Description
Gravitational force This is the attractive force that exists between the masses of the protons and the neutrons. It is a comparatively weak force.
Electrical force The positive charges of the protons in a nucleus create a repulsive force that is comparatively strong to the gravitational forces of attraction.
Strong nuclear force Stronger than the repulsive electrical force, the attractive strong force keeps the protons from flying out of the nucleus. This force has an incredibly short range and is dependent on neutrons.

7.2 Radioactive decayEdit


7.2.1 Describe the phenomenon of natural radioactive decayEdit



7.2.2 Describe the properties of alpha (α) and beta (β) particles and gamma (γ) radiationEdit


7.2.3 Describe the ionizing properties of alpha (α) and beta (β) particles and gamma (γ) radiationEdit



7.2.4 Outline the biological effects of ionizing radiationEdit


7.2.5 Explain why some nuclei are stable while others are unstableEdit



7.2.6 State that radioactive decay is a random and spontaneous process and that the rate of decay decreases exponentially with timeEdit



7.2.7 Define the term radioactive half‑lifeEdit


7.2.8 Determine the half-life of a nuclide from a decay curveEdit


7.2.9 Solve radioactive decay problems involving integral numbers of half-livesEdit



=Nuclear reactionsEdit

7.3.1 Describe and give an example of an artificial (induced) transmutationEdit

7.3.2 Construct and complete nuclear equationsEdit

7.3.3 Define the term unified atomic mass unitEdit

The unified atomic mass unit is the mass of one-twelfth of the nucleus of a carbon-12 isotope

7.3.4 Apply the Einstein mass–energy equivalence relationshipEdit


7.3.5 Define the concepts of mass defect, binding energy and binding energy per nucleonEdit

7.3.6 Draw and annotate a graph showing the variation with nucleon number of the binding energy per nucleonEdit

7.3.7 Solve problems involving mass defect and binding energyEdit

Fission and fusionEdit

7.3.8 Describe the processes of nuclear fission and nuclear fusionEdit

7.3.9 Apply the graph in 7.3.6 to account for the energy release in the processes of fission and fusionEdit

7.3.10 State that nuclear fusion is the main source of the Sun’s energyEdit

7.3.11 Solve problems involving fission and fusion reactionsEdit

Extra stuffEdit





