Understanding Atomic Structure and Radioactivity at GCSE Level

Atomic Structure and Radioactivity

Atomic Models

Over time, our understanding of the atom evolved through various historical models:

• Plum Pudding Model (J.J. Thomson, 1904): Atoms as a sphere of positive charge with negative electrons embedded in it.
• Nuclear Model (Ernest Rutherford, 1911): Atoms have a dense, positively charged nucleus surrounded by orbiting electrons.
• Quantum Model (Niels Bohr, 1913): Electrons occupy specific energy levels around the nucleus.

Atomic Structure

Atoms consist of three fundamental subatomic particles:

• Protons: Positively charged particles in the nucleus.
• Neutrons: Neutral particles in the nucleus.
• Electrons: Negatively charged particles orbiting the nucleus.

Each element has a unique atomic number (number of protons) and mass number (sum of protons and neutrons). Atoms of the same element with different numbers of neutrons are called isotopes.

Radioactive Decay

Unstable atoms undergo radioactive decay, emitting particles or energy:

• Alpha (α) decay: Emission of an alpha particle (two protons and two neutrons).
• Beta (β) decay: Emission of a high-energy electron or positron.
• Gamma (γ) decay: Emission of high-energy electromagnetic radiation.

The time taken for half of the radioactive atoms to decay is called the half-life. Background radiation exists naturally in the environment.

Worked Example: Half-Life

Problem: A radioactive sample has a half-life of 5 days. If it initially has 100 grams, how much will remain after 20 days?

Solution:

• After 5 days (1 half-life), 100/2 = 50 grams remain.
• After 10 days (2 half-lives), 50/2 = 25 grams remain.
• After 15 days (3 half-lives), 25/2 = 12.5 grams remain.
• After 20 days (4 half-lives), 12.5/2 = 6.25 grams remain.

Applications and Hazards

Radioactive materials have various applications, such as:

• Medical imaging and cancer treatment
• Dating techniques (carbon dating)
• Industrial measurement devices

However, exposure to radiation can be hazardous, causing cellular damage and increased risk of cancer. Proper shielding and safety protocols are essential when working with radioactive materials.

Nuclear Fission and Fusion

Nuclear fission is the splitting of heavy nuclei (like uranium) into lighter nuclei, releasing energy. Nuclear fusion is the joining of light nuclei (like hydrogen) to form heavier nuclei, also releasing energy. These processes power nuclear reactors and weapons.