Select your language

Suggested languages for you:
Log In Start studying!
StudySmarter - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
|
|

All-in-one learning app

  • Flashcards
  • NotesNotes
  • ExplanationsExplanations
  • Study Planner
  • Textbook solutions
Start studying

Atoms and Radioactivity

Save Save
Print Print
Edit Edit
Sign up to use all features for free. Sign up now

Want to get better grades?

Nope, I’m not ready yet

Get free, full access to:

  • Flashcards
  • Notes
  • Explanations
  • Study Planner
  • Textbook solutions
Atoms and Radioactivity

Everything you ever touched is made up of atoms. In fact, atoms are the building blocks of all matter in the entire universe. They can contain three main types of subatomic particles, protons, neutrons, and electrons.

All the chemical elements on the periodic table are arranged based on how many protons are in the atomic nuclei. Some of these atomic nuclei are inherently unstable. These are radioactive isotopes. Well-known examples include Uranium, Plutonium, and Thorium. Radioactive atoms are unstable because they have an excess of internal energy within their nucleus. Given time, they will spontaneously undergo a process called radioactive decay to change to a more stable form.

Atoms and radioactive relationships

Measuring radioactivity

We can measure the activity of radioactive sources using a Geiger-Muller tube attached to a counter. Radioactivity is measured using count-rate, meaning the number of decays detected per second. The standard unit of activity is the becquerel (Bq). So, a source that has 10 decays per second would have a count rate of 10 Bq. When a radioactive isotope decays, it emits a radioactive product, commonly an alpha particle, beta particle, or gamma wave. Every time one of these products of radioactive decay enters the Geiger-muller tube, the counter clicks and the count rate is displayed to the operator.

Radioactive isotopes

Different radioactive nuclei will decay at different rates, even between different isotopes of the same element. One isotope might even be stable, while another isotope of the same element is radioactive. More massive elements tend to be more radioactive because their larger nuclei are more likely to have an unstable excess of internal energy.

Atoms and Radioactivity Periodic table showing the half lifes of radioactive elements StudySmarter

Period Table with radioactive elements highlighted according to half-life, adapted from image by Alessio Rolleri CC-BY-SA-2.5

Atoms and Radioactivity: Half-life

An important concept when understanding radioactive decay is a radioactive isotopes half-life. The half-life of a radioactive isotope is defined as the time taken for half the isotopes within a sample to decay. Alternatively, the half-life can be described as the time taken for the count-rate of the sample to be reduced to half its original level. You might be wondering why the half-life is an important thing to learn. The answer is that radioactive decay is random.

Imagine you are studying a single unstable Bismuth-210 nucleus. It would be impossible to determine when it will decay due to the random nature of radioactive decay. However, if you had a 1 kg block of radioactive material containing approximately 1025 Bismuth-210 atoms instead, then you could be nearly certain that some of the radioactive isotopes would decay. If it takes five days for the count rate of the sample to be halved, then you know that the half-life of Bismuth-210 is five days.

Atoms and Radioactivity Radioactive substance decay chart StudySmarterDecay of a radioactive substance, commons.wikimedia

Using the graph above, determine the half-life of the radioactive sample.

Half-life is defined as when half the radioactive isotopes in a sample have decayed. Find the point on the line where the remaining radioactivity is 50%, then determine its x-coordinate to find the time taken to decay.

The radioactive sample has a half-life of 1 year.

Sometimes, the lifespan of a radioactive element is significantly longer than a reasonable observation time. For example, Uranium-238 has a half-life of approximately 4.5 billion years. Scientists can use clever statistical methods to determine when half the unstable nuclei within a sample would have decayed by observing the sample for a relatively short amount of time.

Practically, knowing a materials half-life is useful when evaluating how long it will take before a radioactive sample no longer poses any health risks, such as radioactive waste from a nuclear power plant. An alternative application is the use of a technique called radiocarbon dating, where we can estimate the age of ancient remains.

Carbon-14 is a radioactive isotope of the more common Carbon-12, a stable isotope. Carbon-14 has a half-life of 5730 years. Living organisms contain a lot of carbon, and so do their fossils. By measuring the ratio of Carbon-14 (which decays over time) and Carbon-12 (which does not) in a sample, we can estimate its age.

The structure of an atom and radioactivity

Its actually due to radioactivity that we even understand the underlying structure of the atom at all. After the discovery of the electron in 1897 by J. J. Thomson, the most popular theory of how an atom was structured was the plum pudding model or the Thomson Model. Thomson proposed that negatively charged plums (electrons) were surrounded by a positively charged pudding.

Atoms and Radioactivity Diagram showing the comparison of the Thomson model and the Rutherford model StudySmarterScattering of alpha particles if Plum Pudding model was correct compared to the real results, commons.wikimedia

In 1905, Ernst Rutherford tested the plum pudding model by directing a beam of alpha particles at a strip of gold foil. Alpha particles are a form of radiation with a large positive charge. He expected the alpha particles to pass through the gold with no deflection as the positively charged pudding should be evenly spread out. However, a very small number of the alpha particles were deflected, sometimes being reflected completely.

He proposed that the atom actually consisted of a small, compact, and positively charged nucleus surrounded by a cloud of electrons, called the Rutherford model. The vast majority of the alpha particles passed through the atom without any deflection, proving how small the nucleus was compared to the atom as a whole.

The effects of radioactivity on an atom

A radioactive atom will be changed after undergoing radioactive decay, which can happen in several different ways. Radioactive decay can occur due to an unstable nucleus emitting radiation. The most common forms of decay are alpha particles, beta particles, gamma-rays, or neutron emissions. Each type of radiation has different properties and characteristics.

Atoms and Radioactivity: Alpha radiation

When the nucleus of an atom has too few neutrons compared to protons, it will emit an alpha particle α, which is made from two protons and two neutrons. This helps to restore the balance within the nucleus and reduce the ratio of protons to neutrons.

Atoms and Radioactivity Diagram showing the decay of Americium 241 StudySmarterAn Americium-241 nucleus decays into Neptunium-237 and emits an alpha particle, commons.wikimedia

An alpha particleis exactly the same as a helium nucleus. Therefore, alpha decay will cause the nucleus of an atom to lose a mass number of 4 and a proton number of 2. This is helpful when using nuclear equations, as we are able to determine what element the nucleus will decay into.

A radium (Ra) nucleus emits an alpha particle. What element has the radium nucleus decayed into?

Refer to the periodic table. Radium has a proton number of 88 and a mass number of 226:

One helium nucleus is emitted in alpha decay, so subtract 4 from the mass number and 2 from the proton number of radium:

Determine which element has a proton number of 86 on the periodic table. The answer is Radon, .

Atoms and Radioactivity: Beta particle

Oppositely to alpha decay, if an unstable nucleus has too many neutrons compared to protons, it will emit a beta β particle. A neutron within the nucleus will spontaneously turn into a proton, ejecting a high-velocity electron in the process. The beta particle is literally just one electron.

Atoms and Radioactivity Diagram showing the decay of Caesium 137 StudySmarterA Caesium-137 nucleus decays into Barium-137 and emits a beta particle, commons.wikimedia

Beta decay will cause an atom to change to a different element. Remember that a neutron has been converted into a proton. This will increase the proton number of the nucleus by one but keep the mass number unchanged, as an electron has virtually no mass. A beta particle can be written asorin the context of nuclear equations. The nuclear equation of beta decay of Caesium-137 into Barium-137 shown in the example above is.

Atoms and Radioactivity: Gamma-ray

After an instance of alpha or beta decay, an atomic nucleus will sometimes still have an excess of internal energy. The nucleus will emit this energy in the form of a gamma-ray γ, which is a high-energy electromagnetic wave.

Atoms and Radioactivity Diagram of a radioactive nucleus emmiting a gamma ray StudySmarterRadioactive nucleus decaying by emitting a gamma-ray, commons.wikimedia

Unlike alpha or beta radiation, gamma-rays are waves and not particles. Therefore, during gamma-ray emission, the proton number and mass number remain completely unchanged. It is written asin a nuclear equation. The nucleus loses some energy, but there is no change to the atomic structure.

Atoms and Radioactivity: Neutron emission

Some radioactive isotopes are capable of decay by emitting neutrons η at high velocities. It is most commonly seen during nuclear fission (which is a form of radioactive decay) of high mass radioactive isotopes with a high neutron to proton ratio. Depending on the isotope that is undergoing decay, one or multiple neutrons can be emitted at once.

Atoms and Radioactivity Diagram showing the neutron emmision during fission  StudySmarterNeutron emission during the fission of an atomic nucleus, flickr

When a nucleus emits a neutron, its mass number decreases by 1, but its proton number remains the same. It is generally written as. An atoms designated element depends only on the proton number and not the mass number. This means that neutron emission alone will never change the element of an atom, although it will change it to a different isotope.

Atoms and Radioactivity - Key takeaways

  • Atoms contain three different types of sub-atomic particles, protons, neutrons, and electrons.
  • Some nuclei are inherently unstable due to an excess of energy in the nucleus. These are radioactive isotopes. They will undergo a process called radioactive decay to change to a more stable form.
  • Radioactivity can be measured using a Geiger-Muller tube. Activity is measured in count-rate, and the units of count-rate are the Becquerel (Bq).
  • Different radioactive isotopes will decay at different rates. More massive nuclei tend to be more radioactive, as there is a higher excess of energy in their nuclei.
  • The half-life is the time taken for half the radioactive isotopes in a sample to decay or the time taken for the count rate to be halved. This measurement is taken as radioactive decay is random.
  • Radiation was used to discover the internal structure of the atom.
  • Radioactive nuclei can emit several different types of radiation with different properties and characteristics.
  • Alpha decay occurs when there are too few neutrons compared to protons. An alpha particle is released, consisting of two protons and two neutrons.
  • Beta decay can occur when there are too many neutrons compared to protons. A neutron spontaneously changes into a proton, which ejects a high-velocity electron.
  • The atomic structure of an atom is unchanged during gamma-ray emission, as the radiation takes the form of a wave and not a particle.
  • Neutron emission occurs mainly during the fission of atomic nuclei. Multiple neutrons can be emitted at once.

Frequently Asked Questions about Atoms and Radioactivity

Some atomic nuclei are unstable because of an excess or imbalance of internal energy. They undergo radioactive decay in order to change into a more stable form.

Not all atoms are radioactive. Most elements on the periodic table have at least one isotope with a completely stable nucleus.

Radioactivity cannot destroy atoms. However, splitting an atom (nuclear fission) is actually a form of radioactive decay. The atom is not destroyed, but a lot of energy is released in the process.

Different radioactive nuclei will decay at different rates, even between different isotopes of the same element. More massive elements tend to be more radioactive.

Final Atoms and Radioactivity Quiz

Question

What did Rutherford discover in his alpha scattering experiment?

Show answer

Answer

The alpha particles scattering experiment lead to the discovery of the nucleus. 

Show question

Question

What is the main idea behind John Dalton's atomic theory?

Show answer

Answer

All atoms of an element are the same and atoms are indivisible - they are the smallest structure.

Show question

Question

What is the name of the piece of apparatus used by Thomson to discover the electron and why does it have this name?

Show answer

Answer

It is called a deflection tube. It has this name because the electrons were deflected using oppositely charged metal plates. 

Show question

Question

What model of the atom first included electrons?

Show answer

Answer

The plum pudding model

Show question

Question

Which model of the atom is the one generally used today?

Show answer

Answer

Bohr's model.

Show question

Question

How did Bohr solve the problem of the atom collapsing due to electrons being attracted to the nucleus?

Show answer

Answer

He said that electrons could only exist at fixed energy levels (shells) and were confined to these orbits around the nucleus.

Show question

Question

Does an electron's orbit around the nucleus become larger or smaller as its energy increases?

Show answer

Answer

As its energy increases, an electron's orbit get larger. 

Show question

Question

How did Rutherford conclude that the nucleus is extremely small compared to the size of the atom?

Show answer

Answer

In the alpha scattering experiment, the vast majority of alpha particles passed straight through the gold foil.

Show question

Question

Why did Rutherford conclude that the nucleus accounted for almost all of the mass of the atom?

Show answer

Answer

The alpha particles that were shot at the foil of gold had a large momentum. Therefore, the nucleus had to have a large mass to be able to reflect them backward. 

Show question

Question

What is the name given to the energy levels around the atom in which electrons orbit?

Show answer

Answer

They are called shells.

Show question

Question

How did Thomson conclude that electrons were negatively charged?

Show answer

Answer

He observed them deflect towards a positively charged plate and away from a negatively charged plate.

Show question

Question

Why did Thomson claim that electrons were extremely light?

Show answer

Answer

He observed that they were not affected by gravity significantly. And they moved very easily in the presence of electric and magnetic fields.

Show question

Question

In Thomson's experiment that resulted in the discovery of electrons, what suggested that the rays observed were a stream of particles?

Show answer

Answer

The rays did not split or widen when they were deflected as was expected for waves. Furthermore, the rays were slower than the speed of light.  

Show question

Question

What are the plums, and what is the pudding in the plum pudding model?

Show answer

Answer

The plums represent the electrons, and the pudding represents a positive charge spread out over the atom.

Show question

Question

How was the nucleus found to be positively charged?

Show answer

Answer

During the alpha scattering experiment, it was observed how the positively charged alpha particles were sometimes deflected by large angles. This suggests that the charge must be concentrated in the centre. 

Show question

Question

Name two instruments for detecting radiation.

Show answer

Answer

A photographic plate and a Geiger counter.

Show question

Question

What instrument did Henri Becquerel use to identify the radiation coming from uranium rocks when he first discovered radioactivity in 1896?

Show answer

Answer

A photographic plate.

Show question

Question

What are the three types of radiation?

Show answer

Answer

Alpha, beta, and gamma radiation.

Show question

Question

Alpha radiation is the most penetrating type of radiation. True or false.

Show answer

Answer

False. Gamma radiation is the most penetrating.

Show question

Question

Which type of radiation would be absorbed by a piece of paper?

Show answer

Answer

Alpha radiation.

Show question

Question

What does a Geiger counter measure?

Show answer

Answer

Count rate.

Show question

Question

What is someone's radiation dose?

Show answer

Answer

It is the amount of radiation they are exposed to.

Show question

Question

What is the main type of detector used to measure a person's radiation dose?

Show answer

Answer

A film badge dosimeter.

Show question

Question

Which type of radiation is involve in the process behind a smoke detector?

Show answer

Answer

Alpha radiation.

Show question

Question

Which type of radiation is used for measuring the thickness of materials like paper?

Show answer

Answer

Beta radiation, as alpha would be absorbed and gamma would pass straight through.

Show question

Question

What is background radiation?

Show answer

Answer

It is the small amount of radiation that is always present and we are all exposed to.

Show question

Question

Give two sources of background radiation

Show answer

Answer

eg the air, the earth, food, drink

Show question

Question

Why did Becquerel think that the radiation coming from uranium violated the law of conservation of energy?

Show answer

Answer

The uranium rock in his experiment seemed to emit constant amounts of radiation - this would mean that it had unlimited energy. It is now known that uranium decays over a very long period and the amount of radiation that it emits does not change by much over thousands of years.  

Show question

Question

Give an example of somewhere that you would be exposed to a large amount of radiation.

Show answer

Answer

eg nuclear power plants

Show question

Question

Uranium rocks are radioactive, do they glow with light?

Show answer

Answer

They do not, although this is how they are often depicted. They only glow when placed in 'pools' in nuclear power plants.

Show question

Question

The nucleus is positively charged. True or false.

Show answer

Answer

True.

Show question

Question

What is the mass of the electron in atomic mass units?

Show answer

Answer

0 amu

Show question

Question

What is the relative charge of the proton?

Show answer

Answer

+1

Show question

Question

What two particles make up the nucleus?

Show answer

Answer

Protons and neutrons.

Show question

Question

Where are the electrons in the currently accepted model of the atom?

Show answer

Answer

They orbit the nucleus in shells.

Show question

Question

In nuclide notation, what is the top number called and what does it represent?

Show answer

Answer

It is called the mass number (A) and represents the total number of protons and neutrons.

Show question

Question

In nuclide notation, what is the bottom number called and what does it represent?


Show answer

Answer

It is called the atomic number (Z) and represents the number of protons.

Show question

Question

Does the atomic number or the mass number define what element an atom is?

Show answer

Answer

The atomic number (number of protons) defines the element.

Show question

Question

If an atom is neutral and has an atomic number of 7, how many electrons does it have?

Show answer

Answer

7

Show question

Question

What is the charge of a neutron?

Show answer

Answer

It has no charge.

Show question

Question

What is relative charge measured in?

Show answer

Answer

The electron volt (the magnitude of the charge of the electron).

Show question

Question

What is the definition of the atomic mass unit?

Show answer

Answer

The atomic mass unit is equal to 1/12 of the mass of a carbon-12 atom.

Show question

Question

By how many orders of magnitude are the proton and neutron heavier than the electron?

Show answer

Answer

Roughly 3 orders of magnitude (they are approximately 2000 times as heavy).

Show question

Question

Can atoms of the same element have different numbers of neutrons?

Show answer

Answer

Yes, these are called isotopes.

Show question

Question

Can atoms of the same element have different numbers of protons?


Show answer

Answer

No, the number of protons defines the element.

Show question

Question

What is atomic relative mass? 

Show answer

Answer

The relative atomic mass of an atom Ar is the weighted average mass of all the isotopes of the same element. It also takes into account the abundance of each isotope.

Show question

Question

What is abundance of an isotope? 

Show answer

Answer

It it the percentage of isotopes of the same element found in a naturally occurring sample .

Show question

Question

What are isotopes? 

Show answer

Answer

Isotopes are  atoms of the same elements that have the same proton number and a different neutron number .  

Show question

Question

Which of the following is true?

Show answer

Answer

Isotopes have the same atomic number.

Show question

Question

Which characteristic of an isotope determines its chemical element? 

Show answer

Answer

The atomic number 

Show question

60%

of the users don't pass the Atoms and Radioactivity quiz! Will you pass the quiz?

Start Quiz

Discover the right content for your subjects

No need to cheat if you have everything you need to succeed! Packed into one app!

Study Plan

Be perfectly prepared on time with an individual plan.

Quizzes

Test your knowledge with gamified quizzes.

Flashcards

Create and find flashcards in record time.

Notes

Create beautiful notes faster than ever before.

Study Sets

Have all your study materials in one place.

Documents

Upload unlimited documents and save them online.

Study Analytics

Identify your study strength and weaknesses.

Weekly Goals

Set individual study goals and earn points reaching them.

Smart Reminders

Stop procrastinating with our study reminders.

Rewards

Earn points, unlock badges and level up while studying.

Magic Marker

Create flashcards in notes completely automatically.

Smart Formatting

Create the most beautiful study materials using our templates.

Just Signed up?

Yes
No, I'll do it now

Sign up to highlight and take notes. It’s 100% free.