You will see that electron orbitals look more like a fuzzy cloud of electron distribution without a clear boundary. So how do we define atom size? In this lesson, you 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
- Be reminded how small atoms are
- See the problem of measuring the atom size
- Be introduced to the definition of atomic radius
The aim is to give students a real-life example depicting that there are objects that are hard to measure because you first need to define what the size would be for them.
This example asks students to measure the size of a light spot from a torch. Put a torch in a stand rod, so that the light spot shows on the table surface. Switch off the light and ask the students to measure the light spot. Compare the results from different students.
History and sources of knowledge
- Experiments to measure the 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 smallest atom is helium. Helium was discovered not on Earth but on the Sun.
- The largest atom is caesium, nearly 10 times bigger than helium.
- Give an example of some things (not atom or light spot) that size is not obvious. How can we define their size?
- Calculate the radius of hydrogen if, in its molecule (H2), the distance between two hydrogen nuclei is 0.074 NM.
- Calculate the phosphorus atom radius if a chain of 1,000 side-by-side phosphorus atoms is 200 NM.