Atomic Structure

Summary and Exam Tips for Atomic Structure

Atomic Structure is a subtopic of Principles of Chemistry, which falls under the subject Chemistry in the Edexcel IGCSE curriculum.

• An atom consists of three subatomic particles: protons (positively charged), electrons (negatively charged), and neutrons (no charge). The nucleus, located at the center of the atom, contains protons and neutrons, while electrons are found in the outermost regions called electron shells.
• The relative mass and charge of these particles are crucial: protons have a relative mass of 1 and a charge of +1, neutrons have a mass of 1 and no charge, and electrons have a mass of $\frac{1}{1836}$ and a charge of -1.
• The proton number (atomic number) is the number of protons in an atom's nucleus, while the nucleon number (mass number) is the total number of protons and neutrons. Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
• The Periodic Table is organized by increasing atomic number, grouping elements with similar properties. Elements in the same group have the same number of electrons in their outer shell, influencing their chemical properties.
• Electron structure involves electrons orbiting the nucleus at specific energy levels. The number of electrons each level can hold is determined by the principal quantum number $n$, with the formula $2n^2$.

Exam Tips

• Remember that the mass number is the larger number, often referred to as the "massive number," while the atomic number is the smaller one.
• Understand the relationship between proton number and the arrangement of elements in the Periodic Table.
• Familiarize yourself with the concept of isotopes and their chemical properties.
• Practice calculating the number of neutrons using the formula: $\text{Number of neutrons} = \text{mass number} - \text{atomic number}$.
• Use the formula $2n^2$ to determine the maximum number of electrons in each energy level.