A crack in the solid atom
Radioactivity shows atoms can be divided.
A surprise from some elements
Until the late 19th century, people believed the atom was the smallest piece of matter and could not be divided. Then scientists saw that certain elements give out invisible energy and particles.
What would this tell us about the atom?
What this lesson covers
The idea
Some elements emit invisible energy and particles called radiation, a phenomenon called radioactivity, which shows that atoms are made of smaller particles and are not indivisible.
A surprise from some elements
Until the late 19th century, people believed the atom was the smallest piece of matter and could not be divided. Then scientists saw that certain elements give out invisible energy and particles.
What would this tell us about the atom?
- The atom is made of smaller particles
- The atom is a solid ball with nothing inside
- The atom is the smallest piece of matter
From solid ball to smaller parts
Press Next step to follow the story.
Atoms can be divided
The invisible rays and particles came out of the atom itself. So the atom must have smaller parts inside.
Some elements emit invisible energy and particles called radiation, a phenomenon called radioactivity. This shows that atoms are made of smaller particles and are not indivisible.
Notes
Radioactivity (certain elements emitting invisible radiation) shows that atoms are made of smaller particles, so they are not indivisible.
Check yourself
What is the phenomenon of certain elements emitting invisible energy and particles called?
What did radioactivity show about atoms?
Which statement matches the book?
- Scattering. Scattering is the deflection of particles from their straight path. It is a different idea from emitting radiation.
- Valency. Valency is the combining capacity of an atom. It is a different idea from emitting radiation.
- Radioactivity — correct. Yes!
- They are made of smaller particles — correct. Yes!
- They are the smallest units of matter. That was the belief until the late 19th century. Radioactivity showed it was not correct.
- They cannot change or give out anything. Certain elements emit radiation, so atoms can give out energy and particles.
- Every element emits radiation. The book says that certain elements emit radiation, not that every element does.
- Certain elements emit radiation — correct. Yes!
- Radiation can be seen with the naked eye. Radiation is invisible energy and particles.