P4 - Atomoic Structure Flashcards
Who first proposed the idea that matter is made up of tiny spheres called ‘atomos’?
Democritus
What did John Dalton contribute to atomic theory in 1804?
Matter is made up of tiny spheres (‘atoms’) that couldn’t be broken up, and each element is made up of a different type of atom.
Who discovered electrons and proposed the plum pudding model?
J.J. Thomson
What was the prediction of the plum pudding model regarding alpha particles passing through gold foil?
Most alpha particles would pass straight through or be slightly deflected.
What was the outcome of the alpha scattering experiment conducted in Rutherford’s lab?
Some alpha particles were deflected back, indicating a concentrated mass in the center of the atom.
What does the nuclear model of the atom consist of?
A positively charged nucleus surrounded by a cloud of negative electrons.
Who proposed that electrons orbit the nucleus at certain distances called energy levels?
Niels Bohr
What particles make up the nucleus according to the current model of the atom?
Protons and neutrons
What is the relative charge of a proton?
+1
What is the relative charge of a neutron?
0
What is the relative charge of an electron?
-1
How does the size of the nucleus compare to the size of the atom?
The nucleus is about 10,000 times smaller than the radius of the atom.
What happens to electrons when they gain energy from absorbing EM radiation?
They move to a higher energy level, further from the nucleus.
What occurs when an outer electron leaves the atom?
The atom becomes a positively charged ion.
True or False: The current model of the atom is unlikely to change in the future.
False
Fill in the blank: The current model of the atom includes a nucleus that contains ______ and ______.
protons, neutrons
What was the significance of James Chadwick’s discovery in 1932?
It proved the existence of the neutron, explaining the imbalance between atomic and mass numbers.
What gives the atom its overall size?
Negative electrons whizzing around the outside of the nucleus.
What are isotopes?
Isotopes are atoms with the same number of protons but a different number of neutrons.
What determines the atomic number of an element?
The atomic number is determined by the number of protons in an atom.
How is the mass number of an atom calculated?
The mass number is the number of protons plus the number of neutrons.
What is the relationship between isotopes and atomic number?
Isotopes have the same atomic number but different mass numbers.
What is radioactive decay?
Radioactive decay is the process by which unstable nuclei lose energy by emitting radiation.
What types of ionising radiation are commonly known?
- Alpha radiation
- Beta radiation
- Gamma radiation
What is ionising radiation?
Ionising radiation is radiation that knocks electrons off atoms, creating positive ions.
What are alpha particles composed of?
Alpha particles are composed of two protons and two neutrons.
How far can alpha particles travel in air?
Alpha particles can only travel a few centimeters in air.
What is a common use for alpha radiation?
Alpha radiation is used in smoke detectors.
What are beta particles?
Beta particles are fast-moving electrons emitted by the nucleus.
What is the charge of a beta particle?
The charge of a beta particle is -1.
What materials can beta particles penetrate?
Beta particles can penetrate materials moderately and are absorbed by a sheet of aluminium.
What is the function of beta emitters in industry?
Beta emitters are used to test the thickness of sheets of metal.
What are gamma rays?
Gamma rays are waves of electromagnetic radiation released by the nucleus.
How do gamma rays interact with materials?
Gamma rays can penetrate far into materials and require thick sheets of lead or concrete for absorption.
True or False: Gamma rays are strongly ionising.
False. Gamma rays are weakly ionising.
Fill in the blank: Alpha radiation is when an _______ is emitted from the nucleus.
alpha particle
What do nuclear equations show?
Radioactive decay
They use element symbols to represent the decay process.
What is the form of a nuclear equation?
Atom before decay → atom after decay + radiation emitted
This format illustrates the transformation of the atom during decay.
What is the golden rule for nuclear equations?
The total mass and atomic numbers must be equal on both sides
This ensures the conservation of mass and charge in nuclear reactions.
What happens to the charge and mass of the nucleus during alpha decay?
Charge decreases by 2 and mass decreases by 4
Alpha particles consist of two protons and two neutrons.
What is an alpha particle represented as in nuclear equations?
¿He
An alpha particle can also be referred to as a helium nucleus.
What is the nuclear equation for the decay of Uranium-238 to Thorium-234?
238U → 234Th + 4He
This equation illustrates the transformation of Uranium-238 during alpha decay.
What is emitted during alpha decay?
Gamma rays may be released
Gamma rays can be emitted alongside alpha or beta decay to remove excess energy.
What occurs during beta decay?
A neutron turns into a proton and releases a fast-moving electron
This process increases the atomic number by 1.
What is the effect of beta decay on the mass of the nucleus?
Mass does not change
The number of protons and neutrons remains the same in terms of mass.
How is a beta particle represented in nuclear equations?
β
This symbol indicates the emission of a beta particle during decay.
What is the nuclear equation for the decay of Carbon-14 to Nitrogen-14?
14C → 14N + β
This equation reflects the transformation of Carbon-14 during beta decay.
What do gamma rays do in nuclear decay?
They eliminate excess energy from a nucleus
Gamma rays do not affect the atomic mass or atomic number.
True or False: Gamma rays change the charge or mass of the nucleus.
False
Gamma rays only serve to release energy without altering the nucleus’s composition.
What is the definition of half-life?
The time taken for the number of radioactive nuclei in an isotope to halve.
Half-life can also be described as the time taken for the activity (and so count-rate) to fall to half of its initial value.
What is the relationship between radioactive decay and randomness?
Radioactive decay is entirely random; you can’t predict which nucleus will decay next or when any one will decay.
This randomness applies to all radioactive substances.
What device is used to measure radiation from radioactive substances?
Geiger-Muller tube and counter.
This device records the count-rate, which is the number of radiation counts reaching it per second.
How is activity measured, and what does it represent?
Activity is measured in becquerels (Bq), where 1 Bq is 1 decay per second.
Activity represents the rate at which a radioactive source decays.
What happens to the activity of a radioactive source over time?
The activity decreases as radioactive nuclei decay into stable nuclei.
Older sources emit less radiation.
How can you determine the final activity after two half-lives if the initial activity is 640 Bq?
Final activity is 160 Bq, which is 25% of the initial activity.
Calculation steps: 640 ÷ 2 = 320 (1st half-life), 320 ÷ 2 = 160 (2nd half-life); (160 ÷ 640) × 100 = 25%.
What does a graph of activity against time look like for radioactive decay?
The graph is shaped like a curve that decreases over time.
The half-life can be determined by finding the time interval corresponding to a halving of the activity.
True or False: The activity of a radioactive source can ever reach zero.
False.
The activity never reaches zero, which is why half-life is used to measure decay.
Fill in the blank: The initial activity of a sample is 640 Bq, and after two half-lives, the activity is ______.
160 Bq.
What is the significance of measuring half-life?
It helps to understand the rate at which a radioactive source decays.
This is crucial for applications in medicine, archaeology, and nuclear energy.
What is the term for exposure to radiation?
Irradiation
Irradiation refers to the exposure of objects to radiation from a radioactive source.
Does irradiating an object make it radioactive?
No
Irradiating something does not make it radioactive.
What are common methods to reduce the effects of irradiation?
- Keeping sources in lead-lined boxes
- Standing behind barriers
- Using remote-controlled arms in some industries
These methods help minimize exposure to radiation.
What does contamination refer to?
Radioactive particles getting onto objects
Contamination occurs when unwanted radioactive atoms get onto or into an object.
What can happen if radioactive particles get inside your body?
They might decay, releasing radiation which could cause harm
This makes contamination especially dangerous.
What should be used when handling radioactive sources to avoid contamination?
- Gloves
- Tongs
- Protective suits for industrial workers
These items help prevent radioactive particles from sticking to skin or being inhaled.
Which type of radiation is most dangerous outside the body?
- Beta
- Gamma
Beta and gamma radiation can penetrate the body and reach delicate organs.
Why is alpha radiation less dangerous outside the body?
It can’t penetrate the skin and is easily blocked by a small air gap
This makes alpha radiation less harmful when outside the body.
Which type of radiation is most dangerous inside the body?
Alpha sources
Alpha sources do localized damage, making contamination a major concern.
How do beta sources behave inside the body?
They are less damaging, as radiation is absorbed over a wider area and some passes out of the body
This limits the potential harm compared to alpha radiation.
Which type of radiation has the lowest ionising power inside the body?
Gamma sources
Gamma radiation mostly passes straight out of the body.
Why is research about radiation important?
It helps us understand how different types of radiation affect our bodies
This knowledge improves safety and protective measures when using radioactive sources.
True or False: All types of radiation cause equal harm regardless of the source.
False
The seriousness of irradiation and contamination depends on the type of radiation.
Fill in the blank: Keeping sources in _______ can help reduce irradiation effects.
lead-lined boxes
Lead-lined boxes are commonly used to contain radioactive sources safely.
