MYP Physics Atomic Structure, Particles, Charges and Masses Notes

How Does The Internal Structure Of An Atom Explain Charge, Mass, And Electrical Behaviour Of Matter?

1. Matter is made of atoms, and understanding what is inside an atom explains both everyday materials and many modern technologies.
2. Atomic structure is also a good example of how physics uses models: ideas that start simple, then improve when new evidence appears.

Atomic Models Changed As Evidence Improved

1. Early thinkers such as the ancient Greeks proposed that matter might be made of tiny pieces (atoms), but they did not have experimental evidence or a correct picture of different kinds of atoms.
2. By the late 18th century, chemists noticed that substances react in fixed ratios by mass.
3. This supported the idea that matter comes in discrete units, atoms, which combine in set patterns.
4. As more elements were discovered, chemists organized them in the periodic table, a model that groups elements with similar chemical properties.
5. In the 19th century, Mendeleev left gaps in his periodic table and used patterns to predict undiscovered elements.
6. Those predictions were later confirmed by discoveries such as gallium and germanium.

Atoms Are Not Indivisible: The Key Subatomic Particles

1. For a long time, atoms were thought to be fundamental (unable to be split).
2. This changed in the late 19th century with the discovery of the electron, showing that atoms contain smaller parts.
3. Modern atomic structure is usually introduced using a simplified Rutherford-style model:
   1. A tiny central nucleus contains protons and neutrons.
   2. Electrons occupy the space around the nucleus.
   3. The atom is mostly empty space because the nucleus is extremely small compared with the whole atom.

The Plum Pudding Model of the Atom

1. Scientists proposed that:
   1. The atom was a sphere of positive charge
   2. Negative electrons were embedded throughout this sphere
2. Because this resembled fruit scattered in a pudding, it became known as the plum pudding model
3. The model was accepted as it successfully explained the presence of electrons inside atoms and accounted for the overall neutral charge of atoms.

Limitations of the Plum Pudding Model

1. The model assumed that positive charge was spread evenly throughout the atom.
2. It did not include any region of high mass or high density.
3. As a result, it could not explain the strong deflection of fast-moving particles.

Rutherford’s Nuclear Model

1. Ernest Rutherford investigated how positive charge was arranged inside atoms.
2. He proposed testing atomic structure by firing fast-moving particles at thin metal foil.
3. The results of this experiment could not be explained by the plum pudding model.
4. Most alpha particles passed straight through the gold foil, showing that atoms are mostly empty space.
5. Some alpha particles were slightly deflected, suggesting the presence of a positive charge.