Atomic Structure

What is an atom?

The smallest unit of an element

What are the three main subatomic particles?

Proton, neutron, electron

What charge does a proton have?

+1

What charge does a neutron have?

0 (neutral)

What charge does an electron have?

-1

Where are protons found?

In the nucleus

Where are neutrons found?

In the nucleus

Where are electrons found?

Orbiting nucleus in shells

What is the atomic number?

Number of protons in nucleus

What is the mass number?

Number of protons plus neutrons

How do you calculate number of neutrons in an atom?

Mass number minus atomic number

What is an isotope?

Atom of same element with different number of neutrons

Which particle determines element identity?

Proton

What did John Dalton propose?

Atoms are solid spheres

What did J.J. Thomson discover?

Electron (plum pudding model)

What did Rutherford discover?

Nucleus (gold foil experiment)

What did Bohr propose about electrons?

Electrons orbit nucleus in shells/energy levels

What is nuclear model of atom?

Small, dense nucleus with protons and neutrons, electrons in shells

What is radioactive decay?

Unstable nucleus emits radiation to become more stable

What is ionisation?

Loss/gain of electrons, often due to radiation

What are the three main types of nuclear radiation?

Alpha, beta, gamma

What is an alpha particle?

2 protons and 2 neutrons (helium nucleus)

What is a beta particle?

A fast electron emitted by nucleus

What is gamma radiation?

Electromagnetic wave (high energy photon)

What is the charge of alpha particle?

+2

What is the charge of beta particle?

-1

What is the charge of gamma ray?

No charge

Which radiation is most ionising?

Alpha

Which radiation is least penetrating?

Alpha (blocked by paper/skin)

Which radiation is most penetrating?

Gamma (needs thick lead/concrete to block)

Which radiation travels furthest in air?

Gamma

Describe the penetration of beta radiation.

Moderate; blocked by aluminium foil (~few mm)

What is background radiation?

Natural and artificial radiation always present

Sources of background radiation?

Radon gas, cosmic rays, medical, nuclear industry, food

What does unstable mean in atomic structure?

Nucleus likely to decay and emit radiation

What is a half-life?

Time for half radioactive atoms to decay

What unit is half-life measured in?

Seconds, minutes, hours, years

What type of decay emits an alpha particle?

Alpha decay

What happens in beta decay?

Neutron changes to proton, electron (beta) emitted

What happens in gamma decay?

No change to nucleus, gamma ray emitted from excited nucleus

How does atomic number change in alpha decay?

Decreases by 2

How does mass number change in alpha decay?

Decreases by 4

How does atomic number change in beta decay?

Increases by 1

How does mass number change in beta decay?

Stays the same

Does gamma decay change atomic or mass number?

No change

How is radioactive activity measured?

Geiger-Muller tube (counts per second/min)

What is nuclear fusion?

Joining of two small nuclei to make a larger one; releases energy

What is nuclear fission?

Splitting of large nucleus to release energy

Where does nuclear fusion happen naturally?

In stars, including our Sun

What is a chain reaction (in fission)?

Released neutrons cause further fission events

What are uses of alpha radiation?

Smoke detectors

What are uses of beta radiation?

Thickness control in manufacture (e.g. paper/metal)

What are uses of gamma radiation?

Medical tracers, sterilisation, cancer treatment

Why is radiation harmful?

Ionises cells, can cause tissue damage, cancer

What are precautions for working with radiation?

Minimise exposure, shielding, monitoring, safe disposal

What is radioactive contamination?

Unwanted presence of radioactive material on surfaces/materials

What is irradiation?

Exposure of an object to radiation

How can you reduce contamination risk?

Gloves, tongs, sealing radioactive sources

How can you reduce irradiation risk?

Lead shield, distance, limit time exposed

Why is alpha safe outside body, dangerous inside?

Cannot penetrate skin, but causes severe damage to tissues if ingested/inhaled

What is a medical tracer?

Radioactive substance injected/ingested, followed with detector

Which radiation type is most suitable for tracers?

Gamma or beta (passes through body safely, short half-life)

What should the half-life of a tracer be?

Short—active only during use, not for long

Why are gamma rays used for sterilisation?

High penetration, kills microbes on medical equipment

Why does cosmic ray background fluctuate?

Depends on location, altitude, weather

What is radon gas?

Naturally radioactive gas from rocks/soil

Why is monitoring background radiation important?

Avoid high levels, health/safety

What is a radioactive decay curve?

Graph showing activity decreasing over time

How is half-life found from decay curve?

Time interval for activity to drop from initial value to half

Why is carbon-14 dating useful?

Estimate age of old samples; carbon-14 decays at known rate

What’s a disadvantage of nuclear power?

Long-lived waste, accident risk, high cost

Why don't electrons fall into the nucleus?

They occupy energy levels (shells)

Who proved atom mostly empty space?

Rutherford (gold foil experiment)

How did Bohr improve atomic model?

Quantised electron orbits/shells at fixed distances

What is a cloud chamber?

Detects radiation tracks using condensation trails

What particles are found in nucleus?

Protons and neutrons

Name one way to detect ionising radiation.

Geiger counter, photographic film, scintillation detector, cloud chamber

What does an isotope decay into?

A different element or isotope, emitting radiation

What is the typical energy for nuclear reactions?

Millions of electron volts (MeV)

What does decay mean in physics?

Spontaneous change in unstable nucleus with emission of radiation

If an isotope has a half-life of 10 years, how much remains after 20 years?

1/4 of original amount

What is an alpha emitter useful for?

Smoke alarm, because it’s stopped by air, safe inside device

What is a limitation of gamma in medical imaging?

Exposure risk, needs correct dose and half-life

Why is beta not used for internal tracers?

Moderate penetration, risk to tissue

What is the standard model of the atom?

Current theory: nucleus surrounded by electrons in shells; quarks inside protons/neutrons

What causes background radiation to vary by location?

Natural rocks, cosmic rays, human activity

What is the process by which isotopes emit radiation?

Radioactive decay

How do you calculate the new activity after one half-life?

Divide by two

Why is nuclear fusion not used for power on Earth?

Difficult to sustain high temperature/pressure, not energy efficient currently

What is the main difference between contaminated and irradiated objects?

Contaminated objects continue emitting radiation; irradiated do not

How is nuclear waste stored?

Secure, shielded containment underground

What causes radioactive objects to decrease activity over time?

Natural decay