Answer:
He developed the concept of concentric electron energy levels
Explanation:
Before Bohr's model, Rutherford's model was proposed. This model explains most of the properties of the atom but failed to explain the stability of the atom.
As per Rutherford's model, electrons revolve around the nucleus in the orbit.
But revolving electron in their orbit around nucleus would give up energy and so gradually move towards the nucleus and therefore, eventually collapse.
Bohr's proposed that the electrons around the nucleus move orbit of fixed energy called "stationary states". Electrons in these stationary states do not radiate energy.
Therefore, proposal of concentric electron energy levels refine the atomic models.
A MOLECULE IS MADE OF TWO OR MORE ELEMENTS CHEMICALLY COMBINED IS KNOWN AS A COMPUND.
A MOLECULE IS MADE OF TWO ATOMS IS JUST AN ELEMENT.
A MOLECULE MADE OF TWO OR MORE ELEMENTS IS KNOWN AS A COMPUND.
The compound is Al2O3. The ratio of aluminum to oxygen is 2:3.
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