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Atomic Structure - Coggle Diagram
Atomic Structure
History of the Atom
Dalton (1800)
Atoms are tiny solid spheres
Cannot be divided
J.J. Thomson (1897)
Discovered electron
Plum pudding model
Positive sphere
Negative electrons embedded within
Rutherford, Geiger & Marsden (1911)
Gold foil experiment
Most alpha particles passed straight through
Atom is mostly empty space
Some deflected slightly
Nucleus positively charged
Few reflected back
Nucleus small and dense
Nucleus contains most mass
Rutherford Model (1911)
Small central nucleus
Electrons orbit nucleus
Bohr Model (1913)
Electrons orbit at fixed distances
Electrons occupy specific energy levels
Modern Model
Positive charge divided into protons
Neutrons discovered by Chadwick
Electron shells and energy levels accepted
Isotopes
Element
Atoms with same number of protons
Atomic Number
Number of protons
Mass Number
Protons + neutrons
Isotopes
Same number of protons
Different number of neutrons
Same element
Different mass numbers
Examples
Carbon-12
Carbon-13
Carbon-14
Radioactive Decay
Unstable Nuclei
Random decay
Emit radiation
Alpha Radiation
Helium nucleus
Strongly ionising
Short range
Stopped by paper
Beta Radiation
Fast electron
Moderately ionising
Medium range
Stopped by aluminium
Gamma Radiation
Electromagnetic wave
Weakly ionising
Long range
Stopped by thick lead or concrete
Nuclear Equations
Conservation Rules
Mass number conserved
Atomic number conserved
Alpha Decay
Mass number decreases by 4
Atomic number decreases by 2
Beta Decay
Mass number unchanged
Atomic number increases by 1
Gamma Decay
No change to mass number
No change to atomic number
Atomic Structure
Atom
Positively charged nucleus
Contains protons and neutrons
Negatively charged electrons surround nucleus
Mostly empty space
Radius ≈ 1 × 10⁻¹⁰ m
Nucleus is 10,000 times smaller than atom
Nearly all mass concentrated in nucleus
Subatomic Particles
Proton
Charge +1
Relative mass 1
Neutron
Charge 0
Relative mass 1
Electron
Charge -1
Relative mass 0.0005
Electron Arrangement
Electrons occupy energy levels (shells)
Electrons can move between energy levels
Higher energy level = further from nucleus
Arrangement changes when interacting with EM radiation
Ions
Neutral Atom
Protons = Electrons
Positive Ion
Loses electrons
More protons than electrons
Negative Ion
Gains electrons
More electrons than protons
Atoms and Electromagnetic Radiation
Electron moves to higher energy level
Absorbs electromagnetic radiation
Electron falls to lower energy level
Emits electromagnetic radiation
Ionisation
Electron gains enough energy to leave atom
Positive ion formed
Half-Life
Definition
Time taken for number of undecayed nuclei to halve
Random Process
Cannot predict individual decay
Can predict behaviour of large samples
Uses
Medical tracers
Thickness control
Carbon dating
Uses and Hazards of Radiation
Hazards
Ionisation damages cells
Mutations
Cancer risk
Medical Uses
Gamma sterilisation
Gamma imaging tracers
Radiotherapy
Industrial Uses
Thickness monitoring
Leak detection
Nuclear Fission
Process
Large nucleus absorbs neutron
Nucleus splits
Releases energy
Produces more neutrons
Chain Reaction
Further fission events
Nuclear Power
Controlled chain reaction
Nuclear Fusion
Process
Small nuclei join together
Produces larger nucleus
Releases large amounts of energy
Occurs In
Stars
Sun
Requirements
Extremely high temperature
Extremely high pressure
Background Radiation
Sources
Radon gas from rocks
Cosmic rays from space
Medical exposure
Food and drink
Variation
Different locations have different levels