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- discovered that it was impossible to know neither the momentum of an electron or any subatomic particle and its exact position
- for that he proposed the new theory which is now called the quantum theory
- The quantum theory explains that electrons are not just particles or waves however, electron had it own properties
- electrons are found in orbitals which we know as we move on in this unit we will use the s,d,p and f orbital which essentially will form sigma and pi bonds.

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- Was dicovered that the energy or light that was released by elextrons were expected to be continuous however it is not
- Electrons within a specific energy level do not emit energy themselves
- Electrons transition between energy levels by absorbing or emitting energy
-  Planck called the term 'quantum' to describe these discrete packets of energy, which is similar to Einstein's concept of photons

Limitations:
- He could only provide/explain for atoms with only one electron for example Helium ion or Hydrogen.

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- Rutherford conducted the Gold Foil Experiment
- The experiment was done by shooting alpha particles at thin sheets of gold foil
- Some of those particles were deflected
- The famous gold foil experiment led to the discovery of the atomic nucleus

Limitations:
- All positive charges should experience repulsion
- Didn't consider the full weight of the atom
-  Electrons in motion were expected to emit radiation continuously and lose energy, which could lead to the collapse of atoms.

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- Thomson discovered the electron which he called "corpuscles".
- Thomson thought that electrons were in a positive sphere which meant that they were the negatively charged particles in a spherical cloud of positive charge.

Some of the limitations were disproved by the Gold Foil Experiment which was conducted by Ernest Rutherford.

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- All matter is composed of tiny atoms
- Atoms are unbreakable
- Atoms of the same element are uniform and identical
- Atoms of different elements exhibit variations in both mass and properties
- Atoms combine in rations that are whole numbers

Some limitations they had were they could not explain why atoms of elements combine in the ratio they do.

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Proposed the law of conservation of mass.

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The idea was that matter is composed of tiny particles. They named the particles "A TOMOS" which meant uncuttable or indivisible.