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Atomic Structure | O Level Chemistry (5070) / IGCSE Chemistry | Full Chapter NotesDescription:
Master the full chapter on Atomic Structure for O Level Chemistry 5070 and IGCSE Chemistry. Clear explanations, examples, and exam-focused tips.What you will learn:

Atomic structure and models
Subatomic particles: protons, neutrons, electrons
Atomic number, mass number, isotopic notation
Isotopes and relative atomic mass (Ar) calculations
Electronic configuration (up to Z=20), shells and valence electrons
Ions: cations, anions, noble gas configurations
Link to Periodic Table groups/periods and properties
Basic nuclear ideas and uses of isotopes
Common exam-style questions and pitfalls
Chapter notes:
Key definitions

Atom: The smallest particle of an element that retains its chemical properties.
Element: A pure substance made of only one type of atom.
Compound: A substance formed when two or more elements chemically combine in fixed ratios.
Ion: A charged particle formed by loss or gain of electrons.
Isotope: Atoms of the same element with the same number of protons but different numbers of neutrons.

Subatomic particles and their properties

Proton (p): charge +1, relative mass 1, located in nucleus
Neutron (n): charge 0, relative mass 1, located in nucleus
Electron (e−): charge −1, relative mass ≈0 (1/1836), located in shells around nucleus

Atomic number and mass number

Atomic number ZZZ: number of protons (also equals number of electrons in a neutral atom).
Mass number AAA: total number of protons + neutrons.
Neutrons =A−Z=A-Z=A−Z.
Isotopic/nuclear notation: e.g., chlorine-35 written as 1735Cl^{35}_{17}\text{Cl}1735​Cl.

Isotopes

Same element, different neutron numbers (e.g., 12C^{12}\text{C}12C and 14C^{14}\text{C}14C).
Chemical properties: nearly identical (same electron structure).
Physical properties: can differ (density, boiling point) due to mass differences.
Uses:

14C^{14}\text{C}14C for radiocarbon dating
60Co^{60}\text{Co}60Co for radiotherapy/sterilization
131I^{131}\text{I}131I medical tracers
235U^{235}\text{U}235U nuclear fuel (outside core O Level chemistry detail)



Relative atomic mass (Ar)

Definition: Weighted average mass of an element’s isotopes compared to 1/12 of 12C^{12}\text{C}12C.