The History of Atomic Theory

Lesson Plan - Get It!

Audio:

Atomic theory is a scientific theory stating that all matter is made of tiny particles called atoms.

Everything, including the air we breathe, is considered to be matter. That means atomic theory impacts just about everyone and everything on the earth!

Some scientists even claim atomic theory is the most important scientific development ever!

Atomic theory cannot be credited to just one person. It was developed over hundreds of years by several scientists.

(If you are unsure of exactly what an atom is, it may be a good idea to complete our lesson found under Additional Resources in the right-hand sidebar before moving forward in this lesson.)

Create a chart like the one below in your notebook and complete it while investigating the roles of Democritus, John Dalton, J.J. Thompson, Ernest Rutherford, Niels Bohr, and Erwin Schrödinger in developing atomic theory.

Get ready to explore the microscopic world of atoms, and find out how they came into focus as the basis of all matter!

Discovering the Atom: Heroes of Science

Imagine the world of science as a giant puzzle. Some scientists found pieces of this puzzle, and others put those pieces together to help us understand atoms, the tiny building blocks of everything around us.

Democritus

The story starts with Democritus, an ancient Greek philosopher. He lived over 2,000 years ago and was one of the first people to suggest that everything is made up of tiny, indivisible particles called atoms.

He believed that if you kept cutting something in half, eventually, you would reach a piece so small it couldn't be cut anymore. This was a brilliant idea for his time, even though he couldn't prove it!

John Dalton

Fast forward to the 1800s and meet John Dalton, an English scientist. Dalton took Democritus's idea and developed the first modern atomic theory. He proposed that atoms are solid spheres and that each element is made up of its own kind of atoms.

For example, all oxygen atoms are identical to each other but different from hydrogen atoms. Dalton's work helped lay the foundation for our understanding of chemistry.

J.J. Thomson

Now, meet J.J. Thomson. In 1897, he discovered the electron. Think of electrons as tiny, negatively charged particles inside atoms. Thomson used a special tube called a cathode ray tube to find these particles.

This discovery was like finding out the earth has tiny invisible marbles inside it!

Ernest Rutherford

Next, is Ernest Rutherford, a scientist from New Zealand. In 1911, Rutherford discovered that atoms have a nucleus, a dense center with a positive charge.

He did this by shooting tiny particles at a thin gold foil. Most of the particles passed through, but some bounced back, showing that atoms have a small, dense center. Imagine trying to shoot peas through a basketball net and finding that some peas bounce back because there's a marble in the middle!

Niels Bohr

Then comes Niels Bohr, a brilliant Danish scientist. In 1913, he built on Rutherford's work and proposed that electrons move in specific orbits around the nucleus, much like planets orbit the sun.

This idea helped explain why atoms don't just collapse and why they emit light in certain colors.

Erwin Schrödinger

A final important scientist is Erwin Schrödinger. In 1926, Schrödinger developed a mathematical equation that describes how electrons move around the nucleus of an atom. This was a big leap from the idea of electrons moving in fixed orbits like planets.

Instead, Schrödinger's equation showed that electrons exist in clouds of probability, meaning we can't know exactly where an electron is at any given time, but we can predict where it is likely to be.

This concept is known as quantum mechanics and revolutionized our understanding of the atomic world, revealing that it is even more mysterious and complex than previously thought.

The History of Atomic Theory

Watch this video to learn more about these men and their contributions to atomic theory.

These scientists — Democritus, Dalton, Thomson, Rutherford, Bohr, and Schrödinger — were like detectives, each finding different clues about atoms. Their discoveries helped us understand how atoms are structured and behave.

Thanks to them, we know that atoms are not just tiny, solid balls but have a complex and fascinating inner world.

Science is full of amazing discoveries, and these scientists showed us that by asking questions and experimenting, we can uncover the secrets of the universe!

Review the chart you created.

• Which discovery did you find the most interesting?

Move to the Got It? section to show what you learned.