Unit Overview
Reactivity 1: Stoichiometry and Periodicity
IB Chemistry SLΒ· 5 min read π 15-20% of overall IB Chemistry SL exam
1. Unit at a Glance
This unit splits into two connected core themes: first, quantitative stoichiometry, which gives you the tools to calculate how much of a substance is involved in any chemical reaction, and second, periodicity, which explains how an element's position on the periodic table predicts its physical and chemical behavior.
We start with the mole concept, the foundation of all quantitative chemistry, before moving on to practical calculations for reacting masses, volumes, and concentrations. We then cover the organization of the periodic table, key periodic trends, and end with a survey of common s- and p-block element reactivity.
This unit covers the following core sub-topics:
The mole concept
Introduces the mole as the SI unit for amount of substance and covers basic molar mass calculations.
β β β± 10 min
Reacting masses and volumes
Teaches how to use mole ratios to calculate masses, gas volumes, and solution concentrations for reacting species.
β β β β± 12 min
Periodic table classification of elements
Explains how the periodic table is organized by electron configuration into periods, groups, and blocks.
β β β± 8 min
Periodic trends in atomic properties
Covers trends in atomic radius, ionization energy, electron affinity, and electronegativity across the periodic table.
β β β β± 15 min
S- and p-block element chemistry
Explores the characteristic chemical properties of key groups in the s and p blocks of the periodic table.
β β β β± 12 min
2. Common Pitfalls
Wrong move:
Confusing molar mass of a substance with the mass of a single particle
Why:
Molar mass describes mass per mole of particles, not the mass of one individual atom or molecule
Correct move:
Always label molar mass with units of g molβ»ΒΉ to avoid confusion with mass of a single particle (measured in amu)
Wrong move:
Assuming all periodic trends hold 100% of the time with no exceptions
Why:
Subshell electron stability creates small, regularly tested exceptions to key trends like ionization energy
Correct move:
Memorize common exceptions (e.g. ionization energy drop between groups 2 and 13) for exam questions
Wrong move:
Ignoring state when calculating reaction volumes
Why:
Molar volume rules only apply to gases, not solids or liquids
Correct move:
Check the state symbol of all species before applying volume stoichiometry calculations
3. Quick Reference Cheatsheet
Concept/Formula | Key Expression/Value |
|---|---|
Mole amount calculation | |
Avogadro's constant () | |
Molar volume of ideal gas at STP (IB SL) | |
Atomic radius periodic trend | Decreases across a period, increases down a group |
Ideal gas law |
What's Next
Begin your study of this unit with the first sub-topic on the mole concept, the foundational quantitative tool for all IB Chemistry. After completing all five sub-topics in this unit, you will be ready to move on to the next unit on bonding and chemical structure, which builds heavily on the periodicity concepts you will learn here.