Video Transcript
What step forward from Bohr’s orbital model of the atom was made by Schrödinger in his electron cloud model? (A) Electrons occupy shells with fixed radii. (B) Electrons are moving within a positively charged sphere. (C) Electrons are spread out over space. (D) The nucleus contains particles with mass but no charge. Or (E) the nucleus contains particles with mass and positive charge.
Let’s have a look at the defining characteristics of Bohr’s orbital model of the atom to see how they compare to Schrödinger’s work with the electron cloud model. Bohr’s model was an incredibly important step in the journey of atomic theory. His model suggested that outside of the nucleus, which contains neutrons and protons, the electrons of an atom orbited in distinct energy shells. His model showed that each energy shell based on its radius has a discrete amount of energy. So Bohr’s model showed electrons in orbits of discrete energy amounts.
After more work was done to understand the nature of electrons, the electron cloud model was developed. It was discovered through Heisenberg’s work that an electron’s position and momentum could not simultaneously be known. This became known as the uncertainty principle. Also, electrons have properties of matter and wavelike properties. So using these ideas, Schrödinger proposed that instead of set orbits around the nucleus, electrons exist as a three-dimensional cloud of negative charge. These areas of electron density can be called electron clouds and vary in shape and energy. This is the modern view of the atom and is the accepted model today. With this information in mind, let’s have a look at our answer choices.
Answer choice (A), electrons occupy shells with fixed radii, describes Bohr’s orbital model well. However, the question asks us to identify a step forward from the Bohr model in the electron cloud model. We can eliminate answer choice (A).
Answer choice (B), electrons are moving within a positively charged sphere, suggests that the electron cloud model shows electrons contained within a positive charge. This answer choice does not describe any feature of the electron cloud model. We can eliminate answer choice (B).
Answer choice (C), electrons are spread out over space, summarizes what is shown in the electron cloud model and was not true for the Bohr model. Answer choice (C) is correct.
Let’s rule out answer choices (D) and (E) just to be sure. Both choices discuss the nucleus, which was not a part of any changes from Bohr’s orbital model to Schrödinger’s electron cloud model. We can eliminate both answer choices (D) and (E).
Therefore, the answer choice that describes the step forward from Bohr’s orbital model of the atom made by Schrödinger in his electron cloud model is answer choice (C), electrons are spread out over space.
