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Chapter 5: Problem 19

Explain how we know that atoms have massive, compact nuclei.

Short Answer

Expert verified
The knowledge that atoms have massive, compact nuclei was derived from Ernest Rutherford's gold foil experiment. He discovered that when he bombarded gold foil with alpha particles, some particles were deflected back, indicating that most of the atom's mass and all of its positive charge is concentrated in a compact central region known as the nucleus.

Step by step solution

01

Understand the basics of atomic structure

Before understanding why the atomic nucleus is compact and massive, it's important to know what an atom is. An atom is the most basic unit of a chemical element, and the smallest unit of matter that retains the properties of an element. It consists of a dense, central nucleus surrounded by a cloud of negatively charged electrons.
02

Explore the Rutherford's Gold Foil Experiment

In 1911, Ernest Rutherford conducted an experiment known as the 'Gold Foil Experiment'. He fired positively charged alpha particles at an ultra-thin gold foil. He observed that most of the particles passed straight through the foil, but some particles were deflected back. This was unexpected under the then prevailing 'plum pudding' model of the atom, where the atom was believed to be a diffuse cloud of positive charge in which electrons were embedded.
03

Interpret the results of the gold foil experiment

Rutherford interpreted this unexpected result to mean that the positive charge in the atom must not be spread out, but must be concentrated in a small central region, which he called the nucleus.
04

Deduce the properties of the atomic nucleus

The fact that most of the alpha particles passed straight through suggested that the nucleus was compact, taking up only a tiny fraction of the total space inside an atom. The fact that some particles were repelled with high energy showed that the nucleus was positively charged and massive, because it could repel high-speed, positive alpha particles.

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Most popular questions from this chapter

Obtain a glass prism (or a diffraction grating, which is probably more readily available and is discussed in the next chapter) and look through it at various light sources, such as an ordinary incandescent light, a neon sign, and a mercury vapor street lamp. Do not look at the sun! Looking directly at the Sun causes permanent eye damage or blindness. Do you have any trouble seeing spectra? What do you have to do to see a spectrum? Describe the differences in the spectra of the various light sources you observed.

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