What does Structure of the Atom cover in IB Physics?

This topic covers the historical development of the atomic model and how atomic spectra provide evidence for discrete energy levels. The Geiger-Marsden-Rutherford experiment provided evidence for the existence of the atomic nucleus. Nuclear notation ^A_ZX indicates the nucleon number A and proton number Z.

Is Structure of the Atom SL or HL?

Both. SL and HL students study Structure of the Atom, and HL goes further: the relationship between the radius and the nucleon number for a nucleus, as given by R = R_0 A^1/3, and its implications for nuclear densities.

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Topic E.1 · SL and HL

Structure of the Atom: notes and practice questions

Q: How do I revise Structure of the Atom for IB Physics?

Start from the core idea: this topic covers the historical development of the atomic model and how atomic spectra provide evidence for discrete energy levels. In the exam: both papers, with the scattering and Bohr content HL only. May 2025 HL Paper 2 TZ1 question 3(a) asked, in two parts, explain why alpha scattering deviates from the Rutherford model at high energy (1 mark: the alpha is within range of the strong nuclear force) and explain how an initial energy E_0 estimates the nuclear radius (2 marks: recognize that the nuclear radius is approximately the distance of closest approach, then set initial kinetic energy equal to kQq/r). Then practise exam-style questions, easiest first, writing out every step of your working before you check it.

10 min read Jump to 17 practice questions

Summary

This topic covers the historical development of the atomic model and how atomic spectra provide evidence for discrete energy levels.
The Geiger-Marsden-Rutherford experiment provided evidence for the existence of the atomic nucleus.
Nuclear notation $^A_ZX$ indicates the nucleon number $A$ and proton number $Z$ .
Emission and absorption spectra demonstrate the existence of discrete atomic energy levels.
Photons are emitted or absorbed during atomic transitions.
The energy of a photon is related to its frequency by the equation $E = hf$ .
Emission and absorption spectra provide information about the chemical composition of substances.

How it is examined

Both papers, with the scattering and Bohr content HL only. May 2025 HL Paper 2 TZ1 question 3(a) asked, in two parts, explain why alpha scattering deviates from the Rutherford model at high energy (1 mark: the alpha is within range of the strong nuclear force) and explain how an initial energy $E_0$ estimates the nuclear radius (2 marks: recognize that the nuclear radius is approximately the distance of closest approach, then set initial kinetic energy equal to $kQq/r$ ). The mark scheme said explicitly that using r in an algebraic expression is not enough for the first marking point, which is a good illustration of how tightly "explains" is read.

Given in the booklet

SL: $E = hf$ , Planck's constant, the electronvolt conversion. HL adds $R = R_0 A^{1/3}$ with $R_0$ , the Bohr energy-level formula and $mvr = nh/2\pi$ . Chemical symbols are explicitly not required, so a question that depends on knowing that Au is gold should name the element in words.

Key ideas

the Geiger-Marsden-Rutherford experiment and the discovery of the nucleus
nuclear notation $^{A}_{Z}\text{X}$ , where A is the nucleon number, Z the proton number and X the chemical symbol
that emission and absorption spectra provide evidence for discrete atomic energy levels
that photons are emitted and absorbed during atomic transitions

Not assessed

Recall of chemical symbols is not required.

At HL

the relationship between the radius and the nucleon number for a nucleus, as given by $R = R_0 A^{1/3}$ , and its implications for nuclear densities
deviations from Rutherford scattering at high energies
the distance of closest approach in head-on scattering experiments
the discrete energy levels in the Bohr model for hydrogen, as given by $E = -\dfrac{13.6}{n^2}\ \text{eV}$

Guiding questions

What is the current understanding of the nature of an atom?
What is the role of evidence in the development of models of the atom?
In what ways are previous models of the atom still valid despite recent advances in understanding?

Linking questions

How can emission spectra allow for the properties of stars to be deduced?
How is the distance of closest approach calculated using conservation of energy?
How can emission spectra be used to calculate the distances and velocities of celestial bodies?
Under what circumstances does the Bohr model fail? (NOS)
How have observations led to developments in the model of the atom? (NOS)

Practice questions

17 questions · 7 easy · 8 medium · 2 hard

Showing 17 of 17

Question 1

EasyPaper 1A · calculator1 mark

Which experiment provided the first evidence for a small, dense, positively charged nucleus within the atom?

A. Millikan's oil drop experiment

B. Rutherford's gold foil experiment

C. The Davisson-Germer experiment

D. Thomson's cathode ray tube experiments

Question 2

MediumPaper 1A · calculator1 mark

In a particle scattering experiment, a proton is accelerated from rest through a potential difference of $2.5\text{ MV}$ . The proton is aimed directly at a stationary lithium nucleus. The proton number of lithium is $3$ .

What is the distance of closest approach between the proton and the lithium nucleus?

A. $\frac{3ke}{2.5 \times 10^6}$

B. $\frac{3ke^2}{2.5 \times 10^6}$

C. $\frac{ke}{2.5 \times 10^6}$

D. $\frac{4ke}{2.5 \times 10^6}$

Question 3

HardPaper 2 · calculator9 marks

(a)(i)

A stationary isotope of $_{92}^{238}$ U (Uranium) undergoes alpha decay, transforming into a new element, Thorium (Th), and an alpha particle.

(a)(i) Identify the proton number of the Thorium nucleus.

[1]

(a)(ii)

(a)(ii) The following data are available:

Atomic mass of $^{238}$ U $= 238.050788$ u

Atomic mass of $^{234}$ Th $= 234.043601$ u

Mass of $\alpha = 4.002603$ u

Show that the energy released in this decay is approximately $4.3$ MeV.

[2]

(a)(iii)

(a)(iii) The following data are available:

Atomic mass of $^{238}$ U $= 238.050788$ u

Atomic mass of $^{234}$ Th $= 234.043601$ u

Mass of $\alpha = 4.002603$ u

Calculate the percentage of the total energy released that is carried by the alpha particle.

[2]

(b)(i)

In a historical experiment, a beam of alpha particles was directed at a thin gold foil to probe the structure of the atom.

(b)(i) Describe two key observations from this experiment.

[2]

(b)(ii)

(b)(ii) Outline how these observations led to the nuclear model of the atom.

[2]

Question 4

EasyPaper 1A · calculator1 mark

An ion Y contains the following particles:

$38$ protons

$52$ neutrons

$36$ electrons.

What is the nuclear notation for Y?

A. $^{90}_{38}\text{Y}$

B. $^{88}_{36}\text{Y}$

C. $^{52}_{38}\text{Y}$

D. $^{90}_{36}\text{Y}$

Question 5

MediumPaper 1A · calculator1 mark

A nucleus of element P has a radius $R$ and density $\rho$ .

Another nucleus of element Q has a nucleon number that is $64$ times that of P.

What is the radius and density of the nucleus of Q?

Radius of nucleus of Q	Density of nucleus of Q
$4R$	$64\rho$
$64R$	$4\rho$
$4R$	$\rho$
$64R$	$\rho$

A. $4R$ , $64\rho$

B. $64R$ , $4\rho$

C. $4R$ , $\rho$

D. $64R$ , $\rho$

Question 6

HardPaper 2 · calculator20 marks

(a)

An exoplanet named Xylos orbits a star named Aethel. Scientists are studying its atmospheric conditions and the properties of its host star.

(a) State what is meant by the stellar constant for Xylos.

[1]

(b)(i)

(b) The following data are given for exoplanet Xylos:

Average albedo of Xylos $= 0.40$

Average orbital distance from Aethel $= 2.0 \times 10^{11} \text{ m}$

Average global surface temperature of Xylos $= 250 \text{ K}$

Luminosity of star Aethel $= 2.0 \times 10^{26} \text{ W}$

(i) Outline the physical mechanism by which some of the infrared radiation emitted by the surface of Xylos is absorbed by its atmospheric gases and re-radiated back towards the surface.

[2]

(b)(ii)

(ii) Show that the average global intensity of radiation absorbed by the surface of Xylos is about $60 \text{ W m}^{-2}$ .

[2]

(b)(iii)

(iii) Determine the average intensity re-radiated by Xylos's atmosphere towards its surface. Assume that the emissivity of the surface is $0.95$ .

[3]

(c)

[2]

(d)(i)

(d) A possible fusion reaction occurring in stars like Aethel is the deuterium-tritium (D-T) fusion reaction:

$^2_1\text{H} + ^3_1\text{H} \rightarrow ^4_2\text{He} + ^1_0\text{n}$

Relevant atomic masses are:

Mass of deuterium ( $^2_1\text{H}$ ) $= 2.013553 \text{ u}$

Mass of tritium ( $^3_1\text{H}$ ) $= 3.015501 \text{ u}$

Mass of helium-4 ( $^4_2\text{He}$ ) $= 4.001506 \text{ u}$

Mass of neutron ( $^1_0\text{n}$ ) $= 1.008665 \text{ u}$

(i) Calculate, in $\text{MeV}$ , the energy released in the reaction.

[2]

(d)(ii)

(ii) Outline the role of fusion reactions in maintaining a stable radius for a star like Aethel.

[2]

(d)(iii)

(iii) Outline how the presence of hydrogen in Aethel can be confirmed empirically.

[2]

(e)(i)

(e) Aethel has a surface temperature of $5200 \text{ K}$ and a luminosity $0.5$ times that of the Sun.

(i) State the star type of Aethel.

[1]

(e)(ii)

(ii) Discuss how nuclear fusion processes in a red dwarf star differ from those in the Sun.

[3]

Question 7

EasyPaper 1A · calculator1 mark

A particle accelerator is used to create a specific ion. Analysis shows that a single ion has the following composition:

$38$ protons

$52$ neutrons

$36$ electrons.

What is the nuclear notation for this ion?

A. $^{90}_{38}\text{Y}$

B. $^{52}_{38}\text{Y}$

C. $^{88}_{36}\text{Y}$

D. $^{90}_{36}\text{Y}$

Question 8

MediumPaper 1A · calculator1 mark

An astronomer analyses the spectrum of light received from a distant star. Three assertions are made about this spectrum.

I. The dark lines in the star's absorption spectrum correspond to the emission lines of elements in the star's outer atmosphere.

II. The redshift of these spectral lines can be used to determine the star's surface temperature.

III. The existence of discrete spectral lines provides evidence for the quantization of electron energy levels in atoms.

Which of the assertions are correct?

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

Question 9

EasyPaper 1A · calculator1 mark

In the Geiger-Marsden experiment, a beam of alpha particles was directed at a thin gold foil. What was the key observation that led to the conclusion that the atom has a small, dense, positively charged nucleus?

A. Most alpha particles passed through the foil with no deflection.

B. A small number of alpha particles were deflected by large angles.

C. Alpha particles were observed to have discrete kinetic energies after passing through the foil.

D. The gold foil became electrically charged during the experiment.

Question 10

MediumPaper 1A · calculator1 mark

A graph of the variation with nucleon number $A$ of the binding energy per nucleon is shown.

Graph of binding energy per nucleon (MeV) vs nucleon number A. The curve peaks around A=60 and then gradually decreases.

What is the approximate total energy, in MeV, needed to completely separate the nucleons of a $^{150}_{60}\text{Nd}$ nucleus?

A. $500$

B. $1250$

C. $1320$

D. $1440$

Question 11

EasyPaper 1A · calculator1 mark

In the Geiger-Marsden experiment, a small proportion of alpha particles were observed to be deflected through angles greater than 90°. What was concluded from this observation?

A. The atom is electrically neutral.

B. The nucleus of the atom is positively charged and has a very small volume.

C. Most of the atom consists of empty space.

D. Electrons are located in discrete energy levels.

Question 12

MediumPaper 1A · calculator1 mark

The diagram shows some of the energy levels for a hypothetical atom. The atom is in a cool gas.

Energy level diagram for a hypothetical atom. The ground state E1 is at 0 eV. Excited states are E2 at 6.0 eV, E3 at 8.0 eV, and E4 at 9.0 eV above the ground state. The energy levels get closer together as energy increases.

A continuous spectrum of electromagnetic radiation is passed through the cool gas. Which diagram correctly shows the resulting absorption spectrum?

Four possible absorption spectra labelled A, B, C, and D, plotted against increasing wavelength from left to right. A shows three dark lines getting closer together towards the left (shorter wavelength). B shows three dark lines getting further apart towards the left. C shows three equally spaced dark lines. D shows five dark lines.

A. A

B. B

C. C

D. D

Question 13

EasyPaper 1A · calculator1 mark

Three statements are made regarding atomic spectra.

I. An absorption spectrum is formed when a continuous spectrum of light passes through a cool gas.

II. The frequencies of the lines in an emission spectrum are directly proportional to the energy differences between electron energy levels.

III. The study of atomic spectra provides evidence for the existence of neutrons.

Which of the statements are correct?

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

Question 14

MediumPaper 1A · calculator1 mark

An electron in an atom de-excites from an excited state to the ground state via a two-step cascade. In the first step, a photon of wavelength $\lambda_1$ is emitted. In the second step, a photon of wavelength $\lambda_2$ is emitted. What is the wavelength of a single photon that could cause the excitation from the ground state to the initial excited state?

A. $\lambda_1 + \lambda_2$

B. $|\lambda_1 - \lambda_2|$

C. $\frac{\lambda_1 \lambda_2}{\lambda_1 + \lambda_2}$

D. $\frac{\lambda_1 + \lambda_2}{\lambda_1 \lambda_2}$

Question 15

EasyPaper 1A · calculator1 mark

The Bohr model is successful in predicting the spectral lines of hydrogen. For which of the following systems would the Bohr model also be applicable?

A. A neutral helium atom ( $^4_2\text{He}$ )

B. A singly ionized lithium ion ( $^7_3\text{Li}^+$ )

C. A triply ionized beryllium ion ( $^9_4\text{Be}^{3+}$ )

D. A singly ionized hydrogen molecule ( $\text{H}_2^+$ )

Question 16

MediumPaper 1A · calculator1 mark

The energy of an electron in a hydrogen atom is given by the formula $E_n = -\frac{E_0}{n^2}$ , where $n$ is the principal quantum number and $E_0$ is a positive constant. What is the frequency of a photon that is absorbed when an electron transitions from the state $n=1$ to the state $n=3$ ?

A. $\frac{1}{9} \times \frac{E_0}{h}$

B. $\frac{8}{9} \times \frac{E_0}{h}$

C. $1 \times \frac{E_0}{h}$

D. $\frac{10}{9} \times \frac{E_0}{h}$

Question 17

MediumPaper 1A · calculator1 mark

The diagram shows three energy levels of an atom.

An energy level diagram showing three horizontal lines at levels E0 (lowest), E1 (middle), and E2 (highest) along an energy axis. The gap between E0 and E1 is visibly larger than the gap between E1 and E2.

The frequencies of the photons emitted in all possible transitions between these levels are $f_1$ , $f_2$ and $f_3$ , where $f_1 < f_2 < f_3$ . What are $E_1$ and $E_2$ ?

	$E_1$	$E_2$
A.	$E_0 + hf_2$	$E_0 + hf_3$
B.	$E_0 + hf_1$	$E_0 + hf_3$
C.	$E_0 + hf_2$	$E_0 + hf_1$
D.	$E_0 + hf_3$	$E_0 + hf_2$

Every Structure of the Atom question, marked for you

Every answer is marked mark by mark, IB-style, and the AI tutor helps when you are stuck.

Where marks are lost

Stopping one step short of the conclusion. Two numbers and no sentence is two marks out of three.
Answering a procedure question with a platitude.
Losing precision in Paper 1B. Uniquely to this paper, quoting the right number badly loses marks.

Structure of the Atom: notes and practice questions

How it is examined

Guiding questions

Linking questions

Practice questions

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Question 11

Question 12

Question 13

Question 14

Question 15

Question 16

Question 17

Every Structure of the Atom question, marked for you

Where marks are lost

Practise this topic as a session

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How it is examined

Guiding questions

Linking questions

Practice questions

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Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Question 11

Question 12

Question 13

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Question 15

Question 16

Question 17

Every Structure of the Atom question, marked for you

Where marks are lost

Questions,answered.

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Questions,
answered.

Start with the IB question
bank built for you.