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Course: High school chemistry > Unit 5
Lesson 4: Activity: How does water form droplets on surfaces?Activity: How does water form droplets on surfaces?
Make science come alive in your classroom with this free hands-on activity aligned to high school NGSS standards.
Activity: How does water form droplets on surfaces?
If you’ve ever stared out a window on a rainy day, you’ve probably noticed the rain forming rounded droplets on the glass. You may have seen water “bead up” when you spilled some on a counter or watched a drop of water slowly form into a blob at the lip of a leaky faucet. It turns out that not all liquids behave this way, so what makes water special?
Why does water form droplets instead of spreading out in an even sheet? What aspects of molecular structure cause water to have this property? In this activity, you’ll investigate several liquids, including water, and use your knowledge of molecular polarity to develop an explanation.
Overview
This activity is designed to be completed in two or three 45-minute class periods, with additional time required for follow-up creative projects. The activity consists of the following parts:
- Setting the stage—Students review fundamental concepts related to bond polarity and molecular dipole moments. Students learn that there is a relationship between many properties of a substance and the strength of its intermolecular forces. (20 minutes)
- Investigation (Part 1)—Students observe the effects of a charged wand on streams of different liquids. Students use their observations to draw conclusions about which liquids contain polar molecules and to create models that explain the behavior of the liquids with the charged wand. (25 minutes)
- Investigation (Part 2)—Students collect data on the number of drops of different liquids that will fit on the surface of a penny. Students use their data to draw conclusions about the relative strengths of intermolecular forces in the liquids and to create a model that explains how polar molecules stick together. (25 minutes)
- Investigation (Part 3)—Students use their understanding of intermolecular forces developed in Parts 1 and 2 to make predictions about whether a paperclip will float on the surface of different liquids and about the relative boiling points of liquids. (20 minutes)
- Let's get creative!—Students apply their knowledge to create a digital or paper poster explaining with words and pictures why water droplets are spherical, or nearly spherical. (45 minutes)
- Keep creating!—Students can choose from additional project ideas. Each project encourages students to combine scientific knowledge with creativity to produce something new.
Download the worksheets and get started today!
You can print out this activity or upload it to a digital classroom.
- Student activity guide (15 page worksheet)
- Teacher guide (step-by-step instructions)
NGSS performance expectations
HS-PS1-3. Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.
HS-PS2-6. Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.
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