James Chadwick and the Missing Particle
In the early 1930s, scientists knew that atoms had tiny, dense centers called nuclei. But their picture of the nucleus had a problem: it did not fully explain the mass of atoms. In 1932, British physicist James Chadwick offered a solution. He presented evidence for a previously unconfirmed particle: the neutron.
Chadwick was born on October 20, 1891, in Cheshire, England. He studied physics at the University of Manchester, where he worked with Ernest Rutherford, a scientist whose experiments had helped reveal the atomic nucleus. Chadwick later worked with Rutherford at the University of Cambridge. There, questions about the structure of matter led him toward the discovery that would make him famous.
A problem inside the atom
Atoms are the building blocks of ordinary matter. Each atom has a nucleus surrounded by much lighter particles called electrons. By Chadwick’s time, scientists knew that the nucleus contained positively charged particles called protons. They also knew that electrons carried negative charge.
- substantial:
- Large or important in amount.
- detecting:
- Finding or noticing something, often with a tool or test.
- traces:
- Signs or evidence left behind by something.
- penetrating:
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- recoiling:
- Moving back or away after being struck.
- measurements:
- Results obtained by finding the size, amount, or other value of something.
- transfer:
- To move something from one object or place to another.
- competing:
- Offering different possible answers to the same question.
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Preview questions from this passageShowHide
- 1Why did the mass of an ordinary helium nucleus suggest that protons alone could not explain its structure?
- 2How could a neutral particle solve the problem of nuclear mass without changing nuclear charge?
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About this explanatory article passage for Middle School
“James Chadwick and the Missing Particle” is a explanatory article reading passage about Discovery of the neutron, written for Middle School. It takes about 6 minutes to read (934 words) and comes with an interactive quiz and a printable worksheet with comprehension questions and an answer key.