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OCR Gateway GCSE Chemistry

Revision Notes

Home / GCSE / Chemistry / OCR Gateway / Revision Notes / 1. Particles / 1.2 Atomic Structure / 1.2.1 Atomic Models Through Time


1.2.1 Atomic Models Through Time


Atomic Models Through Time

  • The atomic model developed by scientists has changed over time as experimental evidence has improved our understanding of the structure of atoms
  • In 1803 John Dalton presented his atomic theory based on three key ideas:
    • Matter is made of atoms which are tiny particles that cannot be created, destroyed, or divided
    • Atoms of the same element are identical, and atoms of different elements are different
    • Different atoms combine together to form new substances
  • At the time, the theory was correct but as science developed some parts of Dalton's theory were disproved
  • This is a fundamental feature of science: new experimental evidence may lead to a scientific model being changed or replaced
Changing Models of the Atom, downloadable AS & A Level Physics revision notes
The evolution of models of atomic structure

Thomson's Model


  • In 1897 physicist J.J. Thomson discovered the electron
  • Using a cathode-ray tube he conducted an experiment which identified the electron as a negatively charged subatomic particle, hence proving that atoms are divisible
JJ Thomson Cathode Ray Tube, IGCSE & GCSE Chemistry revision notes
Diagram showing an electron beam deflecting towards the positive plate, proving electrons are negatively charged
  • Based on his investigations Thomson proposed a model of the atom known as the plum pudding model which depicted negative electrons spread throughout soft globules of positively charged material
Plum Pudding Model of the Atom, IGCSE & GCSE Chemistry revision notes
Diagram showing the plum pudding model of the atom

Rutherford, Geiger and Marsden's Model

  • In 1909 Ernest Rutherford presented his model of the atom based on the famous gold foil experiment
  • Working with Geiger and Marsden, Rutherford shot a beam of positively charged particles at a thin sheet of gold foil and based on the plum pudding model, expected the particles to pass through the foil because the positive charge of the nucleus was thought to be evenly spread out
  • Some particles were scattered, however, and a few were deflected directly back, which led him to postulate that most of an atom's mass is concentrated in a region of space at the centre of the atom called the nucleus
  • The results of Rutherford’s scattering experiments did not support the idea that atoms were as described in the plum pudding model, so the model had to be changed
  • In Rutherford's model the atom consists mainly of empty space with the nucleus at the centre and the electrons orbiting in paths around the nucleus
  • This model was known as the nuclear model of the atom
Rutherford's Model of the Atom, IGCSE & GCSE Chemistry revision notes
Diagram showing Ernest Rutherford's nuclear model of the atom

  • In the plum pudding model, atoms were described as being made from electrons embedded within a positive sphere, whereas in the nuclear model the nucleus is a positive structure at the centre of the atom, with negative (and much smaller) electrons ‘orbiting’ around the outside of it

The Bohr Model

  • In 1913 Niels Bohr further developed the nuclear model by proposing that electrons orbit the nucleus in fixed shells or orbitals located at set distances from the nucleus
  • Each orbital has a different energy associated with it, with the higher energy orbitals being located further away from the nucleus
  • This model solved the question of why the atom does not collapse inwards due to the attraction between the positive nucleus and negative electrons circling the nucleus
  • Bohr’s theory and calculations agreed with experimental results
  • Further investigation and experimentation revealed that the nucleus could be divided into smaller particles, each one having the same mass and charge
  • This work led to the discovery of the proton
Niels Bohr’s model of the atom, IGCSE & GCSE Chemistry revision notes
Diagram showing Niels Bohr’s model of the atom


  • 1. Particles
    • 1.1 The Particle Model
      • 1.1.1 The Particle Model
        • 1.1.2 Limitations of the Particle Model
        • 1.2 Atomic Structure
          • 1.2.1 Atomic Models Through Time
            • 1.2.2 Atomic Structure
              • 1.2.3 Calculating the Particles
            • 2. Elements, compounds & mixtures
              • 2.1 Purity & Separating Mixtures
                • 2.1.1 Pure & Impure
                  • 2.1.2 Relative Masses
                    • 2.1.3 Empirical Formula
                      • 2.1.4 Alloys
                        • 2.1.5 Separation Techniques
                          • 2.1.6 Chromatography
                          • 2.2 Bonding
                            • 2.2.1 Metals & Non-Metals
                              • 2.2.2 Electronic Structure
                                • 2.2.3 Ionic Bonding
                                  • 2.2.4 Covalent Bonding
                                    • 2.2.5 Giant Covalent Structures
                                      • 2.2.6 Polymers
                                        • 2.2.7 Metals
                                          • 2.2.8 Atomic Structure & the Periodic Table
                                          • 2.3 Properties of materials
                                            • 2.3.1 Carbon
                                              • 2.3.2 Changes of State
                                                • 2.3.3 Bulk Properties
                                                  • 2.3.4 Nanoparticles
                                                • 3. Chemical Reactions
                                                  • 3.1 Introducing Chemical Reactions
                                                    • 3.1.1 Chemical Symbols & Formulae
                                                      • 3.1.2 Deducing Formulae Using Common Ions
                                                        • 3.1.3 Balancing Chemical Equations
                                                          • 3.1.4 Writing Balanced Ionic Equations
                                                            • 3.1.6 Conservation of Mass
                                                              • 3.1.7 Using Moles to Balance Equations
                                                                • 3.1.8 Calculating Masses from Balanced Equations
                                                                • 3.2 Energetics
                                                                  • 3.2.1 Exothermic & Endothermic Reactions
                                                                    • 3.2.2 Calculating Energy Changes
                                                                    • 3.3 Types of Chemical Reactions
                                                                      • 3.3.1 Oxidation & Reduction
                                                                        • 3.3.2 OxidatIon & Reduction in Terms of Electrons
                                                                          • 3.3.3 Acids & Alkalis
                                                                            • 3.3.4 Neutralisation
                                                                              • 3.3.4 Strong & Weak Acids
                                                                                • 3.3.5 Effect of Hydrogen Ion Concentration on pH
                                                                                • 3.4 Electrolysis
                                                                                  • 3.4.1 Electrolysis
                                                                                    • 3.4.2 Electrolysis of Aqueous Solutions
                                                                                      • 3.4.3 Reactions at Electrodes
                                                                                        • 3.4.4 Half Equations
                                                                                      • 4. Predicting & Identifying Reactions & Products
                                                                                        • 4.1 Predicting Chemical Reactions
                                                                                          • 4.1.1 Group 1
                                                                                            • 4.1.2 Group 7
                                                                                              • 4.1.3 Group 0
                                                                                                • 4.1.4 Transition Metals
                                                                                                  • 4.1.5 The Reactivity Series
                                                                                                  • 4.2 Identifying the Products of Chemical Reactions
                                                                                                    • 4.2.1 Testing for Common Gases
                                                                                                      • 4.2.2 Testing for Aqueous Cations
                                                                                                        • 4.2.3 Testing for Aqueous Anions
                                                                                                          • 4.2.4 Flame Tests
                                                                                                            • 4.2.5 Instrumental Analysis
                                                                                                          • 5. Monitoring & Controlling Chemical Reactions
                                                                                                            • 5.1 Monitoring Chemical Reactions
                                                                                                              • 5.1.1 Concentration in g/dm3
                                                                                                                • 5.1.2 Concentration in mol/dm3
                                                                                                                  • 5.1.3 Titrations
                                                                                                                    • 5.1.5 Gas Volume Calculations
                                                                                                                      • 5.1.6 Yields
                                                                                                                        • 5.1.7 Atom Economy
                                                                                                                          • 5.1.8 Choosing a Reaction Pathway
                                                                                                                          • 5.2 Controlling Reactions
                                                                                                                            • 5.2.1 Measuring Rates
                                                                                                                              • 5.2.2 Rate Graphs
                                                                                                                                • 5.2.3 Change Rates
                                                                                                                                  • 5.2.4 Catalysts & Enzymes
                                                                                                                                  • 5.3 Equilibria
                                                                                                                                    • 5.3.1 Equilibrium
                                                                                                                                      • 5.3.2 Le Chatelier's Principle
                                                                                                                                    • 6.1 Global Challenges
                                                                                                                                      • 6.1 Improving Processes & Products
                                                                                                                                        • 6.1.1 Extracting Metals
                                                                                                                                          • 6.1.2 Biological Extraction Methods
                                                                                                                                            • 6.1.3 The Haber Process
                                                                                                                                              • 6.1.4 Making Fertilisers
                                                                                                                                                • 6.1.5 Explaining the Haber Process
                                                                                                                                                  • 6.1.6 The Contact Process
                                                                                                                                                    • 6.1.7 Life Cycle Assessment
                                                                                                                                                      • 6.1.8 Recycling Materials
                                                                                                                                                        • 6.1.9 Properties & Uses of Alloys
                                                                                                                                                          • 6.1.10 Corrosion of Iron
                                                                                                                                                          • 6.2 Organic chemistry
                                                                                                                                                            • 6.2.1 Alkanes
                                                                                                                                                              • 6.2.2 Alkenes
                                                                                                                                                                • 6.2.3 Addition Polymers
                                                                                                                                                                  • 6.2.4 Condensation Polymers
                                                                                                                                                                    • 6.2.5 DNA
                                                                                                                                                                      • 6.2.6 Alcohols
                                                                                                                                                                        • 6.2.7 Carboxylic Acids
                                                                                                                                                                          • 6.2.8 Crude Oil & Fractional Distillation
                                                                                                                                                                            • 6.2.9 Cracking
                                                                                                                                                                              • 6.2.10 Cells
                                                                                                                                                                              • 6.3 Interpreting & Interacting with Earth Systems
                                                                                                                                                                                • 6.3.1 Origins of the Atmosphere
                                                                                                                                                                                  • 6.3.2 The Greenhouse Effect
                                                                                                                                                                                    • 6.3.3 Climate Change
                                                                                                                                                                                      • 6.3.4 Atmospheric Pollutants
                                                                                                                                                                                        • 6.3.5 Potable Water
                                                                                                                                                                                      • 7. Practical Skills
                                                                                                                                                                                        • 7.1 Practical Skills
                                                                                                                                                                                          • 7.1.1 Reactivity Trends
                                                                                                                                                                                            • 7.1.2 Electrolysis
                                                                                                                                                                                              • 7.1.3 Separation Techniques
                                                                                                                                                                                                • 7.1.4 Distillation
                                                                                                                                                                                                  • 7.1.5 Identification of Species
                                                                                                                                                                                                    • 7.1.6 Titration
                                                                                                                                                                                                      • 7.1.7 Production of Salts
                                                                                                                                                                                                        • 7.1.8 Measuring Rates of Reaction


                                                                                                                                                                                                        DOWNLOAD PDF

                                                                                                                                                                                                      Author: Stewart

                                                                                                                                                                                                      Stewart has been an enthusiastic GCSE, A Level and IB Chemistry teacher for more than 30 years in the UK as well as overseas, and has been an examiner for IB and A Level, also. As a long-standing Head of Department, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams.


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