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THE VISUAL LEARNING STUDIO
See the idea. Understand the connection.
35 visual explanations across 29 chapters, with topic maps throughout the library.
The chapter index will grow as additional notes are prepared. Chapters shown here are a learning collection, not a claim that the entire exam syllabus is complete.
SEE IT. CONNECT IT. EXPLAIN IT.
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Study the expanded notes and the credited detailed textbook lessons. The current chapter index covers core topics; it is not a claim of exhaustive coverage of every examination syllabus. Check the official syllabus and primary references.
Atoms, Ions and the Mole — lesson overview
Atomic bookkeeping
Atomic number Z equals the number of protons. Mass number A equals protons plus neutrons for a specified nuclide. The number of neutrons is A − Z.
A neutral atom has equal numbers of protons and electrons. Ion formation ordinarily changes electron count, not the nucleus’s proton number.
Isotopes have the same atomic number but different neutron numbers. Relative atomic mass in a natural sample is not simply always an integer mass number.
The mole
One mole contains exactly 6.02214076 × 10²³ specified elementary entities. Specify whether the entities are atoms, molecules, ions, or something else.
Amount in moles n = mass m ÷ molar mass M, using compatible units. For example, 18 g of water corresponds to approximately 1 mol when M is taken as 18 g mol⁻¹ at school-level precision.
One mole of water molecules contains two moles of hydrogen atoms and one mole of oxygen atoms. Molecules and constituent atoms must not be counted as the same entity.
Formula and reaction amounts
A chemical formula gives composition: H₂O has two hydrogen atoms per oxygen atom in a molecule. A balanced equation gives the relative amounts reacting.
In 2H₂ + O₂ → 2H₂O, two moles of hydrogen react with one mole of oxygen to produce two moles of water under the represented reaction.
A coefficient does not change the identity of the substance; altering a subscript does. The limiting reactant controls the maximum product when reactant amounts are not in stoichiometric proportion.
