Periodic Trends
Organisation of the Periodic Table · Atomic Radius, Ionic Radius, and Electronegativity Trends
IB Chemistry topic guide
Structure 3: Classification of Matter
Structure 3: Classification of Matter is a core part of IB Chemistry. This guide connects the syllabus ideas behind Periodic Trends, Group Chemistry, Introduction to Organic Chemistry, Isomerism and IUPAC Nomenclature, shows how they appear in worked problems, and points you to the formulas and full lessons needed for exam revision.
What you will learn
Structure 3: Classification of Matter syllabus outline
The units below follow the structure used in the full Study to Learn course. Use the outline to identify exactly which idea needs attention, then work through the public example before continuing to the complete lesson path.
Group Chemistry
Alkali Metals and Halogens · Period 3 Oxides and Chlorides: Bonding and Acid–Base Character
Introduction to Organic Chemistry
Organic Compounds and Homologous Series · Functional Groups and Structural Representation
Isomerism and IUPAC Nomenclature
Structural Isomerism · IUPAC Nomenclature: Systematic Naming
Free worked preview
Organisation of the Periodic Table
This complete preview comes from the Periodic Trends unit. It introduces the core language, shows the method in context, and gives you a real example of the lesson quality before you create an account.
How the Table Is Built
The periodic table is chemistry’s most powerful organising tool — it groups elements with similar properties together and reveals patterns that let you predict behaviour without memorising every element individually. This lesson explains how the table is arranged by atomic number into groups and periods, and how the four blocks (s, p, d, f) correspond to electron configurations. After this lesson, you will understand why elements in the same group share similar chemistry and why the period number matches the outermost electron shell for s- and p-block elements.
The periodic table arranges elements in order of increasing atomic number. Groups (vertical columns): elements with the same number of valence electrons, hence similar chemical properties. Periods (horizontal rows): elements with the same number of occupied electron shells.
The Four Blocks
- s-block (Groups 1–2): outermost electron in an s orbital. Includes highly reactive alkali metals (G1) and alkaline earth metals (G2).
- p-block (Groups 13–18): outermost electron in a p orbital. Includes non-metals, metalloids, the halogens (G17), and noble gases (G18).
- d-block (Groups 3–12): d subshell being filled. Transition metals — characterised by coloured compounds, variable oxidation states, and catalytic activity.
- f-block: f subshell being filled. Lanthanides and actinides, placed separately for display convenience.
Common ErrorThe period number equals the principal quantum number n of the outermost occupied shell for s- and p-block elements, NOT for d-block elements (where the n−1 d subshell is being filled). Iron is in Period 4 because its outermost electrons occupy the n=4 shell (4s), even though its 3d subshell is also being filled.
Reviewed by the Study to Learn editorial team · Updated 2026-08-04