MYP Chemistry Atomic Structure Notes

The Modern Quantum Model of the Atom

1. The structure of the atom has fascinated scientists for centuries.
2. Over time, as new experiments and technologies were developed, our ideas about atoms have changed and improved.
3. The current quantum model of the atom is based on over a hundred years of experimental evidence.
4. It gives us a clearer picture of the tiny building blocks of matter and how they behave.

Early Atomic Models and Subatomic Particles

Dalton’s Atomic Theory – The First Modern Atomic Model

In the early 19th century, John Dalton proposed one of the first scientific models of the atom.

Dalton suggested that:

1. All matter is made up of tiny particles called atoms.
2. Atoms are indivisible – they cannot be split into smaller parts.
3. Atoms of the same element are identical and have the same mass and properties.
4. Atoms of different elements are different and have different masses.
5. A chemical reaction is simply a rearrangement of atoms; atoms are not created or destroyed in the process.

Discovery of Subatomic Particles

1. Later experiments in the late 19th and early 20th centuries showed that Dalton’s model was incomplete:
   1. Electrons were discovered (showing atoms are not indivisible).
   2. Protons and neutrons were discovered in the nucleus.
2. We now know that a typical atom contains three main subatomic particles:
   1. Protons
   2. Neutrons
   3. Electrons
3. These particles are the key building blocks of atomic structure.

The Three Main Subatomic Particles

1. The proton has a positive charge and is found in the nucleus.
2. The neutron has no charge (it is neutral) and is also found in the nucleus.
3. The electron has a negative charge and is found outside the nucleus, in regions we call energy levels or electron shells.

Atomic Mass Unit (u)

The masses of subatomic particles are extremely small, so we use a special unit called the atomic mass unit, symbol u.

Summary Table of Subatomic Particles