Atomic Struct Flashcards
What is the relative charge and mass of protons, neutrons, and electrons?
Proton: Charge +1, Mass 1
Neutron: Charge 0, Mass 1
Electron: Charge -1, Mass ≈0
Define “isotope” and give an example
Isotopes are element with the same number of protons but different numbers of neutrons. Example: Carbon-12 and Carbon-14.
Describe the alpha particle scattering experiment and its conclusions.
Experiment: Fired alpha particles at thin gold foil.
Observations: Most passed through, some deflected, very few bounced back.
Conclusions: Atoms are mostly empty space, have a dense, positively charged nucleus.
Compare the properties of alpha, beta, and gamma radiation.
Alpha (α): He nucleus, highly ionising, weakly penetrating (stopped by paper).
Beta (β): Fast electron, moderately ionising, penetrates a few mm of aluminium.
Gamma (γ): EM wave, weakly ionising, highly penetrating (stopped by thick lead).
Write a balanced nuclear equation for the alpha decay of Uranium-238.
92
238
U→
90
234
Th+
2
4
He
Define “half-life” and explain how it is measured.
Time taken for half the unstable nuclei in a sample to decay or for the activity to halve. Measured by monitoring count rate over time.
A radioactive source has a half-life of 5 hours. If its initial activity is 800 Bq, what will the activity be after 15 hours?
15 hours = 3 half-lives →
800 → 400 → 200 → 100 Bq
Explain the difference between irradiation and contamination
Irradiation: Exposure to radiation without direct contact (temporary).
Contamination: Radioactive particles get onto or inside an object (dangerous).
What are the risks and uses of nuclear radiation in medicine?
Risks: Can cause mutations, cell damage, cancer.
Uses: Radiotherapy, medical tracers (short half-life, gamma).
What is radioactive decay?
The random process by which an unstable nucleus emits radiation (alpha, beta, or gamma) to become more stable.
Name the three types of radiation and describe their nature.
Alpha (α): 2 protons + 2 neutrons (He nucleus).
Beta (β): Fast-moving electron.
Gamma (γ): Electromagnetic wave.
Compare alpha, beta, and gamma radiation in terms of penetration power and ionisation strength.
Alpha: Weak penetration, highly ionising.
Beta: Moderate penetration, moderately ionising.
Gamma: Strong penetration, weakly ionising.
How does beta decay change the nucleus?
A neutron turns into a proton and emits an electron. Atomic number increases by 1, mass number stays the same.
What happens in gamma decay?
The nucleus loses excess energy as a gamma wave, but the atomic and mass numbers remain the same.
What is the equation for calculating remaining activity after multiple half-lives?
Finalactivity=Initialactivity×( 1/2)n
Why is alpha radiation more dangerous inside the body than outside?
Inside, it is highly ionising and can damage cells and DNA. Outside, it cannot penetrate skin.
What safety precautions should be taken when working with radioactive materials?
Use lead shielding (absorbs radiation).
Increase distance from the source.
Handle with tongs to avoid direct contact
FINAL Round what did John Dalton, JJ Thompson, Ernest Rutherford and Bohr invent
John Dalton atom with solid sphere made from different elements
JJ Thompson atoms weren’t solid was a ball on centre with positive charge ‘ plumb pudding’
Ernest Rutherford Alpha particle with gold sheet experiment which shows the nuclues in the middle
Bohrs nucleur model electrons in shells orbit nucleus it contains protons +1 neutrons 0 and electron -1this is the current model.
The actual final Question
State the radius of an atom and the size of its nucleus
Radius of atom = 1x 10-10
Radius of nuclues is 10,000x smaller
