Next Generation Science Standards

Performance Expectation

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.

• Clarification Statement: Emphasis is on understanding the strengths of forces between particles, not on naming specific intermolecular forces (such as dipole-dipole). Examples of particles could include ions, atoms, molecules, and networked materials (such as graphite). Examples of bulk properties of substances could include the melting point and boiling point, vapor pressure, and surface tension.
• Assessment Boundary: Assessment does not include Raoult’s law calculations of vapor pressure.

In this performance expectation, students are going to delve deeper into the inner psyche of a substance than an eHarmony profile. They will plan and conduct an investigation to help them find out what makes these particles tick: what makes them melt, what makes them boil over, and what helps them get together and stay together. In the end, they'll know these substances better than the substances know themselves.

The key is that students will make the connection between what's going on at a subatomic level and what we can observe with our own two eyes.

Ready to play elemental matchmaker with these activity ideas?

• Assign groups of students to research the known melting and boiling points of several elements. Have them record the numbers on a periodic table for the whole class to see. Use their knowledge of atomic structure and the periodic table to discuss and analyze any patterns they may notice.
• Provide students with some beakers, water, rubbing alcohol, and some small paperclips. Have them place the paperclip gently on top of the water and then alcohol, then discuss what they observe. Explain surface tension and have them brainstorm in their groups what causes the water to be able to support the weight of the paperclip.
• Have students develop an experiment to see if they can add a substance to water to change its boiling point. They'll then conduct their experiment and discuss the results in terms of the strength of the forces between the particles involved in the experiment.

Disciplinary Core Ideas

PS1.A – Structure and Properties of Matter: The structure and interactions of matter at the bulk scale are determined by electrical forces within and between atoms.

Students should know that chemicals have many properties. Some of these properties, like melting point or vapor pressure, are the same no matter how much of the chemical we have. We refer to these as bulk properties. Other properties, like mass or volume, change depending on how much of the chemical we have (duh).

Bulk properties are all rooted in the electrical forces that exist within and between atoms. Students should know that the nucleus has a positive charge from the protons, while the electrons provide a negative charge. Also, the number of valence electrons determines the ability of an element to create compounds. So while chlorine exists as a gas when by itself, once bonded up with its buddy, sodium, it forms table salt, which has a melting point of 801 °C. That's a big difference, thanks to just one chemical bond.

There are also intermolecular forces to consider. Polar molecules create partial charges that can then be attracted to each other. Water and its world-famous hydrogen bonds are a prime example of this, giving an otherwise small molecule a huge heat capacity, high melting and boiling points, high surface tension, and all sorts of other properties.

It will be difficult for students to visualize how electrical forces within something as small as an atom determine whether a substance will be sticky, hard, or boil at room temperature. Allow them to work in small groups to get help from their peers and offer guidance if they start to stray off course.

Remember that we're focusing on comparing structures at a bulk scale to learn about the strength of electrical forces between particles. This isn't a vapor pressure torture chamber, so don't force them to make Raoult's law calculations. That's just mean.

PS2.B –Types of Interactions: Attraction and repulsion between electric charges at the atomic scale explain the structure, properties, and transformations of matter, as well as the contact forces between material objects. (Secondary to HS-PS1-3)

Ever wonder why your desk is so…solid? Or why your hair gel is so jiggly? Or why the dorky bumper sticker you put on your car is so hard to remove? Somehow "Honk if you love My Little Pony" isn't so cool when you're driving through the high school parking lot to work…

Students should know that atoms possess electric charges based on their protons and electrons. These charges, much like the charges of a magnet or the personality of their lab partner, have the ability to attract or repel.

Depending on the level of attraction or repulsion, we see different structures and properties. For example, we may observe that our desk is very solid because the particles that make it up are strongly attracted to one another. Electric charges also determine the contact forces between material objects as well. These forces determine if something is sticky or smooth and explain why we can't ice skate on asphalt.

Students should also know that sometimes levels of attraction and repulsion change if conditions, like temperature, change. This can cause a change in state. For example, when we increase the temperature of an ice cube, the attraction between the water molecules isn't strong enough to withstand the increased movement of the molecules and the solid ice becomes liquid water.

Again, it'll be tough for students to grasp that something as small as electrical forces between an atom can determine whether an object is rough or jiggly or sticky or fluffy. Allow them to explore the objects around them and continuously relate their properties back to their atomic structure. Also, provide them with time to discuss with their peers to help solidify their understanding.

Science and Engineering Practices

Planning and Carrying Out Investigations: Plan and conduct an investigation individually and collaboratively to produce data to serve as the basis for evidence, and in the design: decide on types, how much, and accuracy of data needed to produce reliable measurements and consider limitations on the precision of the data (e.g., number of trials, cost, risk, time), and refine the design accordingly.

This is no cookie cutter lab torn out of a crusty copy of Chemistry and You: Unoriginal Labs to Bore Even the Most Enthusiastic Chemistry Student. Students are going to be in charge of planning and conducting their own investigation.

They're not doing it just for the goggles, though. Their goal is to gather data that will help them compare the bulk properties of substances and understand the strength of electrical forces between particles. Any of the ideas we've discussed thus far in this standard are good routes to go. Students just need to do plan and conduct it themselves (with your oversight, of course).

Since they'll be collaborating with their peers on this one, they'll need to come to a consensus on the details of gathering evidence. They'll need to decide what kind of data they'll be collecting, how much they'll be collecting, and when, where, who, and how they'll collect it. If they need to change some aspects of their experiment to accommodate their needs, so be it. As long as it doesn't require them to come in at five o'clock in the morning (and you to be there to supervise), it's all good.

Crosscutting Concepts

Patterns: Different patterns may be observed at each of the scales at which a system is studied and can provide evidence for causality in explanations of phenomena.

There's a reason that patterns pop up in this performance expectation. The periodic table is chock full of them. Students will put their knowledge of atomic structure and the individual properties of elements to use as they plan and execute their experiment.

Their goal is to gather evidence to help them understand how the variations in the strength of electrical forces between particles results in different bulk scale properties. May the force be with them.