Atomic Charge

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Objective

Students explain why electrons are usually the particles that transfer charge based on the basic structure of the atom.

Big Idea

Electrostatic forces are the result of charge: protons have positive charge and electrons have negative charge.

Context and Supplies

Today's class is to introduce a basic model of the atom, the charge of its parts and to expose students to an operating Van de Graaff Generator.  Students also begin to use some basic vocabulary about the atom and electric charge. 

Applied in this lesson is CCSS Math Practice 3: Construct viable arguments and critique the reasoning of others as students do a brief research on the four fundamental forces. NGSS Science Practice 2: Developing and using models is also applied as students are reminded of the familiar model of the atom with the nucleus in the center with electrons "orbiting". Students also explain why it is electrons that typically transfer charge which applies Science Practice 7: Engaging in argument from evidence.

NGSS Performance standard HS-PS2-6 is the context of this lesson, as this information is needed in order for students to later "Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials." This also leads to the application of HS-PS2-4:Use mathematical representations of Newton’s Law of Gravitation and Coulomb’s Law to describe and predict the gravitational and electrostatic forces between objects.

Homework Video Review - Size of the Atom

10 minutes

For homework, students watch a TED-Ed video on The Size of the Atom. The purpose of the activity is to remind students of the structure of the atom, sub-atomic particles and hopefully amaze them with just how small an atom really is. 

To ensure students do their homework, which includes brief notes on the video, I give them a short Size of the Atom - Socrative Quiz (About Socrative).  It is a four question quiz whose purpose is to give a snap-shot of what the students learn from the video and what they are most amazed about in relation to the size of the atom. In order to take the Socrative quiz, most students use their smart phones, but there are laptops available for the few who don't have a smart phone. This quiz is set so that Socrative.com reveals student's names and their responses as they give them (only I can see the results). I know within the first few minutes of class if there are misunderstandings that need to be addressed.  

Structure of the Atom Lecture

30 minutes

The primary purpose of this time is to remind students about the structure of the atom and reinforce the concept of a fixed nucleus with electrons surrounding the nucleus. They also review the charge of subatomic particles and how like charges repel and unlike charges attract. I say remind because students have learned much of this material years earlier in middle-school and then again in chemistry. 

The beginning of the Atom Basics Power Point instructs students to spend 5 minutes to research the four fundamental forces of the universe. They use the classroom physics textbooks or can go online with their smart phones. Though we can name dozens, if not hundreds of different forces, it is important that students know that all of them are a result of one or more of the 4 fundamental forces. Rather than tell them the forces, I give them five minutes to look it up and try to create a brief explanation. They are to write their answers in their notebooks and when 5 minutes are up, I call on random students to supply what they found. The big idea is to understand that electric force is caused by charges, this is the theme of the rest of the power point. For the next 10 minutes, students take notes on the structure of the atom and charge carriers. Then the period closes with a fun demonstration using the van de Graaff generator where students get to see electrons jump a 5-10 inch gap.

Van de Graff Generator Demonstration

10 minutes

There are two goals with this initial demonstration with the van de Graff Generator. The first is to get the students excited about the study of electrostatics.  Eyes go wide as they see and hear the sparks jump. The second goal is to reinforce the concept presented in the lecture that electrons are the charge carrier in most examples of charge transfer on Earth. We begin to build up vocabulary as I discuss charge build-up, discharge and grounding. 

To start the demo, I turn on the generator. You can hear it sizzle as the air becomes ionized. Then I bring a grounded metal sphere near the van de Graaff generator until a spark jumps. If conditions are right, it can go 4-5 inches through the air. I explain that you need about 20,000 volts to get electricity through 1 inch of air, so we have upwards of 100,000 volts build up on our van de Graaff generator. I turn off the lights so that students can see the mini-lightning bolts clearly. I put my palm on the generator and after a few seconds remove my hand and give a student a fist bump. This results in harmless discharge. After a few minutes, I invite a few student volunteers up to touch the generator. I inform them that they want to use their knuckles to touch it as the finger tips are sensitive. 

As class ends, I instruct the students to watch another TED-Ed video tonight for home work. This one is by James Shiels and is on The Electric Vocabulary