Understanding Atomic Structure and Radioactivity in GCSE Physics

Atomic Structure and Radioactivity

The Structure of Atoms

An atom is the smallest unit of an element that retains its chemical properties. It consists of three fundamental subatomic particles:

• Protons (positively charged)
• Neutrons (neutral charge)
• Electrons (negatively charged)

Protons and neutrons make up the dense nucleus at the center of the atom, while electrons orbit the nucleus in shells or energy levels.

Atomic Models

Our understanding of atomic structure has evolved through various historical models:

• Plum Pudding Model (J.J. Thomson, 1904): Proposed that atoms were positively charged with electrons embedded in them.
• Nuclear Model (Ernest Rutherford, 1911): Established the existence of a dense, positively charged nucleus surrounded by orbiting electrons.
• Quantum Model (Niels Bohr, 1913): Introduced the concept of fixed electron orbits or energy levels.

Atomic and Mass Numbers

The atomic number (Z) represents the number of protons in an atom's nucleus, which determines the element's identity. The mass number (A) is the sum of protons and neutrons in the nucleus.

Isotopes

Isotopes are atoms of the same element with different numbers of neutrons and, consequently, different mass numbers. For example, carbon-12 (12C) and carbon-13 (13C) are isotopes of carbon.

Worked Example

Problem: Determine the number of protons, neutrons, and electrons in an atom with the following characteristics: 14N, Z = 7.

Solution:

• The atomic number (Z) is 7, which means the atom has 7 protons.
• The mass number (A) is 14, and since A = protons + neutrons, the number of neutrons is 14 - 7 = 7.
• In a neutral atom, the number of electrons is equal to the number of protons, which is 7.

Radioactive Decay and Radiation

Certain unstable isotopes undergo radioactive decay, emitting one of three types of radiation:

• Alpha (α) particles: Composed of two protons and two neutrons, emitted from heavy nuclei.
• Beta (β) particles: High-energy electrons emitted from the nucleus.
• Gamma (γ) rays: High-energy electromagnetic waves emitted during nuclear transitions.

Half-Life and Background Radiation

The half-life of a radioactive isotope is the time it takes for half of the atoms to decay. Background radiation refers to the low levels of ionizing radiation present in the environment from natural and man-made sources.

Applications and Hazards

Radioactive isotopes have various applications in medicine, industry, and scientific research. However, exposure to ionizing radiation can pose health risks, such as increased cancer risk and genetic mutations. Proper safety measures and regulations are essential when working with radioactive materials.

Nuclear Fission and Fusion

Nuclear fission is the splitting of heavy nuclei (e.g., uranium-235) to release energy, which powers nuclear reactors and atomic bombs. Nuclear fusion is the merging of light nuclei (e.g., hydrogen isotopes) to form heavier nuclei, releasing vast amounts of energy, as in stars and experimental fusion reactors.