Video: Comparing Thomson’s Plum Pudding Model vs. Dalton’s Hard-Sphere Model of an Atom

How was the plum pudding model different from the hard-sphere model of the atom? [A] The plum pudding model showed electrons making up the corners of a cube. [B] The plum pudding model described electrons orbiting a central nucleus. [C] The plum pudding model included negatively charged particles known as electrons. [D] The plum pudding model included positively charged particles known as protons. [E] The plum pudding model showed electrons occupying different energy levels.

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Video Transcript

How was the plum pudding model different from the hard-sphere model of the atom? (A) The plum pudding model showed electrons making up the corners of a cube. (B) The plum pudding model described electrons orbiting a central nucleus. (C) The plum pudding model included negatively charged particles known as electrons. (D) The plum pudding model included positively charged particles known as protons. Or (E) the plum pudding model showed electrons occupying different energy levels.

The hard-sphere model of the atom was the first atomic model. It was proposed by Dalton. In this model, the atom is the smallest division of matter. The plum pudding model of the atom came afterwards. It was proposed by J. J. Thomson who discovered the negatively charged electrons inside atoms. So the plum pudding model is different from the hard-sphere model of the atom because in the hard sphere model of the atom, the atom is the smallest division of matter. But in the plum pudding model, there is a negatively charged electron which is smaller than an atom. So let’s go through our answer choices to see which of them reflects that.

Answer choice (A) says that the plum pudding model shows electrons making up the corners of a cube. In the plum pudding model, the electrons are embedded in a sea of positive charge. They don’t make up the corners of a cube. This is actually a reference to Lewis’s cubic model of the atom. So it’s not the correct answer choice. The second answer choice says that the plum pudding model described electrons orbiting a central nucleus. The nucleus of the atom wasn’t discovered until after the plum pudding model was proposed. This answer choice is actually a reference to Rutherford’s planetary model of the atom. So it’s not the one we’re looking for.

The next answer choice says that the plum pudding model included negatively charged particles known as electrons. This answer choice sounds like it’s exactly what we’re looking for. The plum pudding model is different from the hard-sphere model because it includes these negatively charged electrons. But let’s go ahead and take a look at our other answer choices just so we know why they’re incorrect. The fourth answer choice says that the plum pudding model includes positively charged particles known as protons. This answer choice is, again, a reference to Rutherford’s planetary model of the atom, as he suggested the term proton to describe the positively charged particles that made up the nucleus.

Our final answer choice says that the plum pudding model showed electrons occupying different energy levels. This answer choice is referring to Bohr’s model of the atom, where electrons occupy fixed energy orbits around the nucleus. So as we discussed before, the plum pudding model is different from the hard-sphere model of the atom because the plum pudding model included negatively charged particles known as electrons.

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