History of the atom

Question 1

John Dalton - when? what?

Answer 1

1803, Solid Sphere Model
- suggesting that all matter is made of indivisible atoms (cannot be created, subdivided, or destroyed)
- building blocks of matter
- Atoms of the same element are identical in mass and properties
- Atoms of different elements are different in mass and properties
- Atoms combine in fixed ratios to form compounds
- He treated atoms as solid, indivisible spheres and did not include subatomic particles

Question 2

J.J. Thomspon - when? what?

Answer 2

1897, Plum Pudding Model
- Discovered the electron through his experiments with cathode rays, showing that atoms contain smaller, negatively charged particles
- Proposed the atom is a positive pudding with negatively charged electrons embedded like “plums” into it
- First model to include subatomic particles

Question 3

Ernest Rutherford - when? what?

Answer 3

1911, Nuclear Model
- Discovered that most of the atom’s mass is concentrated in its small, positively charged nucleus through his gold foil experiment
- Proposed that the atom has a tiny dense nucleus at its centre, containing positively charged protons
- Electrons orbit around this nucleus in a most empty space

Question 4

Niels Bohr - when? what?

Answer 4

1913, Planetary Model
- Refined Rutherford’s model by proposing electrons exist in energy levels around the nucleus
- Electrons orbit the nucleus in fixed orbits and can jump between these levels by absorbing or emitting specific amounts of energy
- Explained the stability of the atom
- Worked well for hydrogen but failed to predict the behaviour of electrons in larger atoms

Question 5

James Chadwick

Answer 5

1932, Neutron Model
- Discovered the neutron
- Proposed that the nucleus consists of both protons and neutrons, which provided a better understanding of atomic mass and stability
- This discovery completed the picture of the nucleus, explaining why atoms of the same element can have different masses (isotopes)

Question 6

Quantum Mechanical Model

Answer 6

1926 Schrodinger
- Proposed that electrons exist in regions called orbitals, which are probability clouds rather than fixed orbits
- This model uses complex mathematical functions to predict electron positions, acknowledging that we cannot determine an electron’s exact location and momentum simultaneously
- Provides a more accurate description of atomic behaviour, especially for larger atoms

Question 7

Why are scientific models important?

Answer 7

Simplification of complex concepts
Visualisation
Prediction
Testing and refinement

Question 8

What are limitations of scientific models?

Answer 8

• they are simplified so do not capture all details of reality

Question 9

Scientific law

Answer 9

statement that describes an observable occurrence in nature that appears to always be true