Students will see that electron orbitals look more like a fuzzy cloud of electron distribution without clear boundaries. So how is atom size defined? In this lesson, students will be introduced to several ways to define atom size.
This lesson is a part of MEL Chemistry VR. Learn more →
atoms, atomic structure, electrons, atom size, atomic radius
- Atoms have clearly-defined size and spherical shape.
- Recall how small atoms are
- See the problem of measuring atomic size
- Examine the definition of atomic radius
The aim is to give students a real-life example depicting objects that are hard to measure because you first need to define what their size would be.
This example asks students to measure the size of a light spot from a flashlight. Put a flashlight in a stand, so that the light spot shows on the table surface. Switch off the overhead light and ask the students to measure the light spot. Compare the results from different students.
History and sources of knowledge
- Experiments to measure atom size: Rayleigh experiment with oil.
- Modern methods: X-ray and spectroscopy.
Topics to discuss
- Not everything can be precisely measured.
- Importance of a definition.
- Different ways to define atomic size.
- Atomic size of metals.
Fun facts and quotes
- The atom with the smallest radius is helium. Helium was discovered not on Earth, but on the Sun. The atom with the largest radius is caesium, nearly 10 times bigger than helium.
- Give an example of something (not an atom or a light spot) where size is not obvious. How can we define its size?
Please see below for the link to a Google form containing a quiz on the material above.
This can be assigned during class time or as homework. The quizzes are marked and the system shows which questions students get correct and incorrect. Please note that students should record their scores, as they will not be viewable later.