GCSE Physics: Atomic Structure

Atomic Structure

The study of atomic structure is fundamental to understanding the nature of matter. Atoms are the basic building blocks of all substances, and their structure determines the properties of elements and compounds.

Structure of Atoms

An atom consists of three main subatomic particles:

• Protons: Positively charged particles found in the nucleus.
• Neutrons: Neutral particles, also located in the nucleus.
• Electrons: Negatively charged particles that orbit the nucleus in energy levels.

The atomic number of an element is defined by the number of protons in its nucleus, while the mass number is the total number of protons and neutrons.

Isotopes

Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons. This results in different mass numbers. For example, carbon-12 and carbon-14 are isotopes of carbon.

Historical Models of the Atom

Over time, several models have been proposed to explain atomic structure:

• Plum Pudding Model: Proposed by J.J. Thomson, this model suggested that atoms are composed of a positively charged 'soup' with negatively charged electrons scattered throughout.
• Nuclear Model: Proposed by Ernest Rutherford, this model introduced the idea of a dense nucleus surrounded by orbiting electrons.

Radioactive Decay

Radioactivity refers to the process by which unstable atomic nuclei lose energy by emitting radiation. There are three main types of radioactive decay:

• Alpha Decay: Involves the emission of an alpha particle (2 protons and 2 neutrons). This decreases the atomic number by 2.
• Beta Decay: Involves the conversion of a neutron into a proton and the emission of a beta particle (an electron). This increases the atomic number by 1.
• Gamma Decay: Involves the emission of gamma rays, which are high-energy photons, without changing the atomic number or mass number.

Half-Life

The half-life of a radioactive isotope is the time taken for half of the radioactive nuclei in a sample to decay. This concept is crucial for understanding the stability and longevity of isotopes.

Background Radiation

Background radiation is the ionizing radiation present in the environment from natural and artificial sources. It is important to understand its levels and sources to assess safety and health risks.

Hazards and Uses of Radiation

While radiation has beneficial uses in medicine (e.g., cancer treatment, imaging), it also poses hazards, including radiation sickness and increased cancer risk. Proper safety measures are essential when working with radioactive materials.

Nuclear Fission and Fusion

Nuclear fission is the process of splitting a heavy nucleus into smaller nuclei, releasing a significant amount of energy. This principle is used in nuclear reactors. Conversely, nuclear fusion involves combining light nuclei to form a heavier nucleus, which powers stars, including our sun.

Worked Example: Calculating Half-Life

Problem: A radioactive isotope has a half-life of 5 years. If you start with 80 grams, how much will remain after 15 years?

Solution:

• After 5 years (1 half-life): 80 g → 40 g
• After 10 years (2 half-lives): 40 g → 20 g
• After 15 years (3 half-lives): 20 g → 10 g

Thus, after 15 years, 10 grams of the isotope will remain.