Classifying Matter


Samples of an element, a compound, and a mixture may look similar “on the outside.” But when we talk about these concepts with students, we are asking them to see what they look like “on the inside”—we want them to imagine atoms, molecules, and mixtures and notice how they are different. This “nuts and bolts” demonstration will help your students visualize abstract concepts relating to the classification of matter.


  • Element
  • Compound
  • Mixture
  • Classification of Matter


Bolts, small 25*
Hex nuts and washers to fit, 25*
Overhead projector
Petri dishes with covers, plastic, 10*
*Materials included in kit.

Safety Precautions

Although the materials in this demonstration are considered nonhazardous, follow all normal laboratory safety guidelines.


None required. Seal the Petri dishes with tape and reuse them every year.

Prelab Preparation

Label a set of Petri dishes A–I and place the following objects in each.

  1. 5 bolts
  2. 6 nuts
  3. 6 washers
  4. 3 bolts and 3 nuts (not assembled)
  5. 2 bolts, 2 nuts and 2 washers (not assembled)
  6. 3 “nut-and-bolt” assemblies
  7. 2 “nut-bolt-washer” assemblies
  8. 2 “nut-and-bolt” assemblies and 2 extra bolts or nuts"
  9. 2 “nut-and-bolt” assemblies and 2 “nut-bolt-washer” assemblies


  1. Distribute Classifying Matter Data Sheet to each student.
  2. Randomly select one of the Petri dishes and place it on the overhead projector. Note: Keep a record of displayed order.
  3. Tell the students to imagine that each object represents either an atom or a molecule. Ask them to silently identify whether the collection of objects in the Petri dish represents an element, a compound or a mixture. Allow students time to record their observation on the data sheet.
  4. Repeat steps 2 and 3 with the other Petri dishes. To keep the students guessing, continue selecting the Petri dishes at random from the available set.
  5. After all of the Petri dishes have been shown, discuss the findings with the class.

Student Worksheet PDF


Teacher Tips

  • This kit contains an extra Petri dish and extra nuts and bolts. Be creative and make up another “nuts-and-bolts” sample to test your students.
  • An alternative way to conduct this demonstration is to place the dishes on lab benches around the room and have students circulate around the room to examine the samples and complete a data sheet.
  • Other questions to ask the students include: are the contents homogeneous or heterogeneous; name a real example corresponding to the type of substance in each Petri dish; what characteristics of a “nut-and-bolt” assembly resemble a molecule.

Correlation to Next Generation Science Standards (NGSS)

Science & Engineering Practices

Developing and using models

Disciplinary Core Ideas

MS-PS1.A: Structure and Properties of Matter
HS-PS1.A: Structure and Properties of Matter

Crosscutting Concepts

Systems and system models

Performance Expectations

MS-PS1-1. Develop models to describe the atomic composition of simple molecules and extended structures.

Sample Data



Do not focus on “right and wrong” answers during the classroom discussion. Encourage students to share their reasoning with the class so they can discover the abstract concepts on their own. Use the following figures and questions as a follow-up assessment after the demonstration.


Next Generation Science Standards and NGSS are registered trademarks of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.