# Atom size

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 VR Science Simulations. Learn more →

## Teacher's notes

### Key­words

atoms, atom­ic struc­ture, elec­trons, atom size, atom­ic ra­dius

### Com­mon mis­con­cep­tions

• Atoms have clear­ly-de­fined size and spher­i­cal shape.

### Stu­dents will

• Re­call how small atoms are
• See the prob­lem of mea­sur­ing atom­ic size
• Ex­am­ine the def­i­ni­tion of atom­ic ra­dius

### Hands-on ac­tiv­i­ties

#### Be­fore VR

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.

### 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.

### Ques­tions

• Give an ex­am­ple of some­thing (not an atom or a light spot) where size is not ob­vi­ous. How can we de­fine its size?

### Quiz

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.

https://forms.gle/8bfd­jjyPqB­n­Jy­dx­c9