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© 2015 SERP SciGen Unit 8.4 1

SMALL,SMALLER, SMALLEST

SciGen Unit 8.4

science

SCIENCE ACTIVITIES

Session 1 Reader’s Theater Settling the Score

2–5

Session 2 Speaking Scientifically

6–8

Session 3 Stuff Changes

9–14

Session 4 Zap that Water!

15–19

Session 5 Writing

20–22

SUPPLEMENTARY ACTIVITIES FOR OTHER CONTENT AREAS

ELA The Theory of Theory

23–25

Math Balancing Chemical Reaction Equations

26–28

Social Studies Elements and Experience

29

FOCUS WORDS

Examining the Focus Words Closely 30



Adam: Hey, Aunt Lucy! These are the best brownies ever. Thanks for baking them.

Aunt Lucy: (from another room) You’re welcome. You guys can go ahead and finish them up.

Zena: There are just two left. Olivia, you’re the guest here, so you can have one. Adam, let’s make the other one last a while. Let’s play halfsies.

Olivia: (with a mouthful of brownie) What’s “halfsies”?

Zena: That’s where one of us takes half, and then the other takes half of what’s left, and we go back and forth like that forever, so that we’re never completely done eating the brownie.

Adam: Well, that’s unfair, because whoever goes first gets half of the whole, plus more pieces later. But on top of that, the whole idea is crazy because we would have to finish the brownie sooner or later. Eventually, someone will eat the last crumb.

Zena: I’ll let you go first, so you don’t have to worry about the fairness thing. It’s worth it to me because it’s not ridiculous. Playing halfsies will make the brownie last forever. Forever, I tell you! (She laughs like a mad scientist in a movie. Adam rolls his eyes.) There will always be another half left, no matter how small a half it is. There’s no such thing as a smallest particle of brownie. It might take a magnifying glass, a razor blade, and a steady hand, but we’ll keep cutting those crumbs in half!

Adam: That’s the goofiest idea I’ve ever heard. Obviously at some point, the remaining crumb of brownie would get too small to see, even with a magnifying glass. And at some point, you would get down to a crumb that was smaller than the width of the edge of a razor blade. So you couldn’t cut it.

Zena: (waving her hand dismissively) I don’t care about those practical problems. In fact, you can have the whole brownie for all I care, but only if you admit that I’m right in theory. Just for the sake of argument, imagine that every time we cut the brownie in half, we also got a magnifying glass that was twice as powerful as the one we used before, and a knife that was twice as sharp as the one we used before. With those magical tools, we could keep dividing the brownie in half no matter how small it got, and we’d never be done.

Olivia: Um, if you guys are just going to talk, can I have that last brownie?

Zena and Adam: No!

Adam: Even if we could always use greater magnification and a sharper knife, I think at some point we would come to a smallest piece of brownie.

Zena: Why? Whatever piece you’ve got must have two halves, right? Just like in math, there’s no number so small that you can’t divide it by two.

Adam: I’m saying that once you cut the brownie enough times, you would get to a particle so tiny that if you cut it apart, you wouldn’t have brownie any more. Instead you’d have…I don’t know…maybe tiny pieces of the ingredients that went into the brownie in the first place. You’d be cutting a tiny piece of sugar away from a tiny piece of flour, salt, baking powder, egg, or chocolate. A brownie is only a brownie if it has all those things, so you’d be breaking your teeny-weeny crumb into parts that aren’t brownie substance anymore.

It’s like if you take a parking lot full of cars and keep dividing it in half, you still have cars for a while. But at some point, you get down to one car. After that, if you keep dividing, you end up with some part of a car—a wheel or a bumper or something—but that’s not a car anymore.

Zena: A car is made of separate parts, but I think that’s different from a brownie. A brownie is made of ingredients, but they’re all blended together into a smooth batter, and when you cook the batter, they all sort of dissolve and melt together and puff up in some kind of chemical reaction, right? And it all becomes—ta da!—solid brownie through and through. And then it’s halfsies, baby, forever and ever!

Adam: I bet Aunt Lucy would know about this. She took a lot of chemistry in college for her engineering degree, didn’t she? Hey, Aunt Lucy—

Aunt Lucy: (coming into the room) Hey, yeah, I couldn’t help overhearing your conversation. Actually, you two are repeating a very old argument about the nature of matter. Back in ancient Greece, there was a philosopher named Democritus who believed that everything was made of tiny particles he called atoms. He thought an atom was the smallest piece of something and couldn’t be cut in half.

Reader’s Theater

Session 1

Playing Halfsies

Setting: Adam and Zena are over at their Aunt Lucy’s house after school, with their friend Olivia.


Olivia: So that’s like Adam’s theory, right?

Aunt Lucy: Right, Adam’s theory of atoms. But not everyone agreed with Democritus. Another philosopher named Aristotle had an especially negative reaction to atomic theory. Aristotle couldn’t imagine absolutely empty space between particles of matter. He wrote that “nature abhors a vacuum,” meaning there is no such thing as space without any matter in it. Since he couldn’t imagine empty space between atoms, he didn’t believe in atoms. He thought matter had to be continuous instead of separated into particles. So for Aristotle, there was no smallest possible piece of a substance.

Olivia: That’s like Zena’s theory that brownies could be divided in half infinitely, if you had a sharp enough knife.

Aunt Lucy: Right. Aristotle thought of matter as being continuous, flowing together without any gaps, like water. Democritus thought of matter as being made of particles. He compared the basic structure of all matter to sand, not water. Democritus thought even water was like sand, if only we could look at it closely enough.

But Aristotle was much more famous and influential than Democritus. So people believed for thousands of years that Aristotle was right about matter being continuous, not particulate. It wasn’t until the start of the nineteenth century that chemists started taking atomic theory seriously again.

Zena: The nineteenth century is the 1800s, right? Why did scientists start believing in atoms then?

Aunt Lucy: Scientists observed various things about the behavior of matter that were easier to explain with atomic theory than without it. The evidence convinced them atoms were real.

Adam: What sort of evidence?

Aunt Lucy: (leaving the room) Why don’t you three look into that?

Olivia: So…Do you guys want to go thirdsies on that last brownie?

Adam and Zena: No!

This cartoon sums up the disagreement between Democritus and Aristotle over the existence of atoms. The crab and the seagull notice that the ancient philosophers are sometimes long on opinion but short on evidence. In the next section, you’ll consider some of the scientific evidence that has influenced the discussion of atoms over the last couple centuries.


Reader’s Theater

Session 1

Playing Halfsies


The kinetic theory of gases: It may seem strange to think of gases—like air, or steam, or helium in a balloon—as being made of particles. But from the eighteenth century onward, physicists have found that thinking of gases as being made of zillions of invisibly small particles bouncing around like balls actually helps explain a lot of things about air pressure and temperature—and about how seagulls fly!

Read these descriptions of various pieces of evidence that Adam and Zena found. For each one, check a box showing whether you think it supports an atomic model of matter (like Democritus’) or a nonatomic model of matter (like Aristotle’s).

Brownian motion: Have you ever noticed how specks of dust dance and twirl in a beam of sunlight? In 1827, a botanist named Robert Brown noticed something similar, at an even smaller scale. He was looking through a microscope at pollen grains in water, and noticed that tiny particles from the pollen moved around in a random, jittery way that he couldn’t easily explain. Brownian motion was eventually interpreted as evidence that invisibly small atoms were bumping into the larger, visible particles and causing them to move.

This evidence supports:

Atomic model Continuous model Not sure

This evidence supports:



Settling the Score

Session 1

Democritus’ Atomic View vs. Aristotle’s Nonatomic View


Say “cheese,” little atoms!

In the 1980s, a complex technique called scanning tunneling microscopy (STM) finally allowed scientists to generate images that show the individual atoms on the surfaces of objects.

Compare notes with your classmates. Two thousand years later, who’s winning the debate on atoms, Democritus or Aristotle? What do you think is the most convincing evidence for or against atoms? Explain.

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This evidence supports



Settling the Score

Session 1

Democritus’ Atomic View vs. Aristotle’s Nonatomic View


water (H2O) carbon dioxide (CO2) ammonia (NH3)

Everything is made of atoms. Atoms are not all identical. In fact, there are over 100 kinds of atoms. About 92 of them occur naturally, and the others have been made by scientists in the laboratory. There are hydrogen atoms, helium atoms, carbon atoms, oxygen atoms, and so on. Substances that are made of just one kind of atom are called elements. Atoms of the same element are all essentially alike, and they’re different from atoms of other elements. (Later on, you’ll learn more about what makes atoms the same or different.)

Some other elements that may sound familiar are nitrogen, neon, silicon, sulfur, copper, silver, gold, and mercury. Less familiar elements include technetium, tantalum, astatine, and promethium. Don’t worry, you don’t have to remember all these names!

If atoms were only found in their elemental form, there would only be about 100 different substances in the world. But there are millions of different substances. Chemists study substances and how they change through the rearrangement of their atoms. The great variety of substances in the world is possible because the atoms of different elements join together to form compounds. Together, elements and compounds are called chemicals. A chemical does not have to be some fancy substance cooked up in a laboratory. Everything, from the air you breathe to the materials in your body, is made of chemicals.

Some common compounds are water, carbon dioxide (which you exhale with every breath), and ammonia (which is often used in cleaning fluids). Compounds have definite proportions of the elements that go into them. For example, water always has twice as many hydrogen atoms as oxygen atoms; carbon dioxide always has one carbon atom for every two oxygen atoms; and ammonia always has one nitrogen atom for every three hydrogen atoms. Here are illustrations of each of these three compounds:

The three compounds above use atoms of these elements (their chemical symbols follow the names):

Again, compounds are made of definite proportions of elements. Look at the images above and fill in these ratios with the smallest possible whole numbers:

• Water has ____ hydrogen atom(s) per ____ oxygen atom(s).

• Carbon dioxide has ____ oxygen atom(s) per ____ carbon atom(s).

• Ammonia has ____ hydrogen atom(s) per ____ nitrogen atom(s).

hydrogen (H)oxygen (O)carbon (C)

nitrogen (N)


Speaking Scientifically

Session 2


The atoms in all three of our compound examples on the previous page are grouped together into larger particles called molecules. A molecule is a group of two or more atoms linked together in a particle with a clearly defined boundary. Just as atoms are the smallest particles of elements, molecules are the smallest particles of molecular compounds like water, carbon dioxide, and ammonia.

Here’s an illustration of a small (a very, very small!) sample of water at a molecular level. Note: The water molecules don’t float in the water. They are the water! Between them there’s nothing but empty space, which is called vacuum.

Not all molecules are compounds, though. Many elements (substances made of one kind of atom) come in molecular form. For example, oxygen and hydrogen gas are typically found in the form of molecules with two atoms each.

oxygen molecule (O2) hydrogen molecule (H2)

A less common form of oxygen is “ozone,” which is made of molecules with three oxygen atoms each. There’s a layer of ozone gas high in the atmosphere that helps protect our skin from the sun’s radiation. On the other hand, ozone at ground level can cause asthma attacks and damage lung tissue. It’s one of the main ingredients in the mixture of air pollution known as smog.

All three of these are examples of the element oxygen, because they’re made without any other kinds of atoms:

oxygen molecule (O2) ozone molecule (O3)oxygen atom (not a molecule)



Session 2


Actually, scientists knew about elements and compounds before they knew about atoms. They knew that some substances (like water) could be divided into others (like oxygen and hydrogen) that couldn’t be further divided into simpler substances. Any substance that couldn’t be divided into simpler substances was called an element. Atomic theory clarifies why elements can’t be separated into other substances: There are only oxygen atoms in oxygen, and there are only hydrogen atoms in hydrogen. So while scientists originally identified elements by their observable behavior, they have come to further define elements by the uniformity—the sameness—of their atoms.

What kind of particle?

Working with a partner, complete the table below:

Check off the terms that apply for each of the samples below. The first two are done for you:

Each particle is... … either an element or a compound, and… ...either an atom or a molecule.

an element (made of only one kind of atom)

a compound (made of more than one element, in definite proportions)

an atom (the smallest particle of an element)

a molecule (a particle made of more than one atom)

This particle of water is... X X

This particle of oxygen is... X X

This particle of nitrogen is...

This particle of ammonia is...

This particle of carbon dioxide is...

This particle of oxygen is...

This particle of hydrogen is...

�

�

�

�

�

�

�



Session 2


In order to form compounds, atoms of different elements must come together in a process called a chemical reaction. A chemical reaction can also break a compound into its separate elements, or change one set of compounds into a different set of compounds. The same atoms exist throughout the process of a chemical reaction, but they’re put together in different combinations before and after the reaction.

Not every change is a chemical reaction. For example, when an iron nail gets bent, the iron atoms get rearranged, but no new substance is formed.

unbent bent

familiar view

particulate view

Because no new substance is formed when you bend a nail, bending is considered a “physical change” rather than a chemical reaction.

Now, if you leave your iron nail lying around in a moist environment, something quite different happens: The nail rusts. It turns brown and crumbly, starting on the outside and continuing toward the center. It loses strength. A new compound with different elemental ingredients and different properties is being produced, an iron oxide with three oxygen atoms for every two iron atoms (Fe2O3). Water molecules are also embedded here and there in the rust.


Stuff Changes

Session 3


iron rust

familiar view

particulate view

So rusting results in a new substance, and that means that it’s a chemical reaction. Scientists say that the iron in the nail reacts with water and oxygen in the air to produce rust. Iron, oxygen, and water are the reactants in this reaction, and rust is the product.

Water itself cab be produced by many different chemical reactions. One of the simplest is the burning of hydrogen gas. Saying that hydrogen “burns” is an everyday way of saying that it reacts with oxygen. The diagram below shows pictures of the molecular reactants and products of this reaction. Then it shows the “equation” for the reaction, using chemical formulas with element symbols and numbers to show how many of each kind of atom and molecule are involved. To begin getting a sense of how to read a chemical reaction equation, compare the images and the equation with the captions beneath them:


Stuff Changes

Session 3


In a chemical equation, the big numbers written before the formula for a compound show how many molecules of that compound are used or produced in the reaction compared to the other compounds. The small numbers below and to the right of element symbols are called “subscript” numbers. (“Sub” means under, and “script” means writing, so subscript numbers hang down under the main level of the writing.) The subscript numbers refer to the elements in front of them, and show how many atoms of each element go into a compound. For example, an H2O molecule has two hydrogen atoms and one oxygen atom.

Note that no atoms are destroyed or created in a chemical reaction. Atoms are just rearranged. In the example of hydrogen and oxygen reacting to produce water, there are two oxygen atoms and four hydrogen atoms before and after the reaction takes place. Since the mass of the substances involved is just the mass of the atoms, there is no change of mass in the reaction. This sameness of mass in reactants and products in chemical reactions is called the Law of Conservation of Matter, because mass is conserved (kept the same) in chemical reactions.

One of the most important chemical reactions for life on earth takes place in plants and is called photosynthesis. Plants take in carbon dioxide (CO2) and water (H2O), and, with a little help from the sunshine, produce oxygen molecules (O2) and sugar molecules. The sugar molecules provide food to animals, but are also used by plants as basic building blocks for their own woody and leafy bodies.

There are several kinds of sugar molecules, all made of carbon, hydrogen, and oxygen atoms. One basic sugar molecule is glucose. A glucose molecule is compounded of 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms, giving it a chemical formula of C6H12O6.

Compare the following representations of photosynthesis. First comes an illustration of the molecules involved, and then comes the chemical reaction equation:

Translated into plain English, the equation says the following:

“Six molecules of carbon dioxide gas and six molecules of liquid water react to produce one molecule of solid glucose and six molecules of oxygen gas.”

6CO2(g) + 6H2O(l) ⟶ C6H12O6(s) + 6O2(g)

water carbon dioxide glucose oxygen


Stuff Changes

Session 3


6CO2(g) + 6H2O(l) ⟶ C6H12O6(s) + 6O2(g)

The full-size numbers in front of compound formulas are “coefficients.” They tell you how many molecules of the compound go into the reaction. (For the glucose molecule in this equation, which does not have a coefficient written in front of it, the coefficient is understood to be 1.)

The small “subscript” numbers within the chemical formulas for compounds tell you how many atoms of the element in front of the subscript go into the compound. (Where no subscript appears, the number is understood to be 1.)

The lowercase letters in parentheses after chemical formulas tell you whether each compound is solid (s), liquid (l), or gaseous (g) in this reaction.

The arrow separates the reactants from the products and tells you which way the reaction goes. Some reactions are reversible, and may show a double arrow: ⇄

Here are some notes to help you

understand how to read a chemical equation…


Stuff Changes

Session 3

water carbon dioxide glucose oxygen


Track that Change

With a partner, use the illustration and the equation for photosynthesis on the previous page to answer the following questions:

What are the reactants in photosynthesis? ________________________________

What are the products of photosynthesis? ________________________________

To answer the next six questions, you can multiply the coefficients in front of the chemical formulas by the subscript numbers within the formulas, and/or count the atoms in the illustration:

How many carbon atoms are there in the reactants? ________

How many carbon atoms are there in the products? ________

How many hydrogen atoms are there in the reactants? ________

How many hydrogen atoms are there in the products? ________

How many oxygen atoms are there in the reactants? ________

How many oxygen atoms are there in the products? ________

Are any atoms destroyed or created during the reaction? ________

Big Amounts from Small Equations

Molecules are so small that we would never notice if just 6 carbon dioxide molecules reacted with 6 water molecules to produce a single glucose molecule and 6 oxygen molecules. You couldn’t see or taste just one glucose molecule!

Within the green leaf of a plant on a sunny day, millions of glucose molecules may be produced every second. What makes the equation for photosynthesis so powerful is that the coefficients in front of the chemical formulas give us proportions of reactants and products that can be scaled up to much larger numbers. It’s sort of like multiplying all the ingredients in a brownie recipe so you can make an extra big batch. But in the case of chemical equations, the ingredients listed as molecules are multiplied by truly gigantic numbers in real life.


Stuff Changes

Session 3


With a partner, answer the following questions:

Suppose that instead of 6 carbon dioxide molecules and 6 water molecules, you start with 6 trillion carbon dioxide molecules and 6 trillion water molecules. How many glucose molecules can you get? ___________________

Suppose a photosynthetic reaction produces 5 billion glucose molecules. How many oxygen molecules are produced by the same reaction? _______________________

Gases have mass, just as solids and liquids do. (Strange but true!) If you get a combined mass of 100 kg of glucose and oxygen from a photosynthetic reaction, what was the combined mass of the carbon dioxide and water that went into the reaction? ____________________

Glucose and other simple sugars are the building blocks from which a tree puts together the tons of solid matter in its woody, leafy body. So over a number of years, using sunlight to drive the photosynthetic reaction, an acorn basically assembles itself into a big old oak tree from rainwater and from carbon dioxide in the atmosphere.

The number of atoms in 100 kg of matter is many times the number of grains

of sand on all the beaches in the world!


Stuff Changes

Session 3


Yesterday you looked at a chemical reaction in which a compound gets put together: Plants put sugar molecules together through photosynthesis. Today you’ll look at a chemical reaction in which a familiar compound, water, gets taken apart.

When you run an electrical current through water (with salt dissolved in the water to help conduct the electricity), water molecules get broken apart into their elemental ingredients, hydrogen and oxygen. This process of breaking water molecules apart with electricity is called “electrolysis.”

A simple, small-scale electrolysis chemical reaction can be set up with the following materials:

• one 9-volt battery

• two wires (one red, one black) with alligator clips at both ends

• two wooden pencils, each sharpened at both ends

• one glass of water

• a small amount (about a tablespoon per cup of water) of epsom salt, which is another name for magnesium sulfate (MgSO4)

• one piece of light cardboard cut so that it can rest on the rim of the glass of water; the cardboard needs to have two X’s cut into it so that it can hold the pencils upright, with one end of each pencil in the water and one end above the cardboard

Isn’t electrolysis also the name of a hair

removal process that works by zapping hair follicles?

Yes, but that’s a whole

different thing.


Zap that Water!

Session 4


Next, attach the wires to the upper tips of the pencils. Make sure the alligator clips are in contact with the pencils’ graphite. The graphite will conduct electricity, just as the metal in the wires does. The wood acts as an insulator, just like the plastic covering on the wires. The graphite tips in the water will act as “electrodes.” The pencil connected to the negative terminal forms the negative electrode, and the pencil connected to the positive terminal forms the positive electrode. This electrode has a

negative electrical charge.

This electrode has a positive electrical charge.

4

Stir the epsom salt (MgSO4) into the water. Dissolving this in the water will help the electricity flow through the water better.

Put the cardboard on top of the glass, with the two pencils inserted so that each has one end in the water.

Attach the red wire to the positive terminal of the battery and the black wire to the negative terminal.

31 2


Zap that Water!

Session 4


What’s with the bubbles?

If the water were heating up, you might speculate that it was boiling, and that the bubbles were made of steam. But the water isn’t getting hotter. In fact, it gets slightly colder in this reaction!

The gas bubbles that formed on the electrodes are actually hydrogen gas (at the negative electrode) and oxygen gas (at the positive electrode).

There is actually slightly less water after the bubbles form. Does this mean that this electrolysis reaction violates the Law of Conservation of Matter? Nope. The mass of the water that gets used up (converted to gas) in the reaction is exactly equal to the combined mass of hydrogen and oxygen gas produced in the reaction.

It may seem strange to think of gases as having mass, but they do!

On a large scale, electrolysis can produce enough hydrogen to use as fuel for hydrogen-powered vehicles and other applications. Because it isn’t economical to store extremely large amounts of energy in electric batteries, production of hydrogen fuel through electrolysis can be a good way of storing energy produced by electrical power plants for later use.

5

Once the battery is connected to the pencils, bubbles form at the tips of the pencils under water. Usually more bubbles form on the pencil attached to the negative terminal of the battery (with the black wire) than on the positive terminal (with the red wire).

Bubbles form at electrodes.


Zap that Water!

Session 4


John Dalton (and friends)

Illustration from Dalton’s “A New System of Chemical Philosophy,” showing his symbols for atoms of different elements and his idea of how they combine to form compounds. Published in 1808.

Summary of key ideas and terms: A compound (like water, H2O) is a substance made of definite proportions of other, simpler substances. Compounds are produced and taken apart by chemical reactions. Matter is conserved in chemical reactions. Elements (like hydrogen and oxygen) are the simplest chemical ingredients that combine to make compounds. Atoms are the smallest particles of elements. Atoms can stick together to form larger particles called molecules. There can be molecules of pure elements (like O2 and H2) and of compounds (like

Comparing the masses of reactants and products in chemical reactions led John Dalton to the modern theory of atoms in 1803. Through countless experiments over many years, atomic theory has gone from being the nearly-forgotten speculation of Democritus to being a basic part of the modern scientific understanding of the physical world.


Zap that Water!

Session 4


Beholding Bubbles, Picturing Particles, and Naming Names

Complete the labels for these illustrations of the electrolysis reaction by filling in the blanks:

In an electrolysis reaction, two water molecules produce two hydrogen molecules and one oxygen _________.

One oxygen _________ can be divided into two oxygen _________.

An oxygen ________ cannot be divided into a smaller piece of oxygen.

Each water _________ has 2 _________ atoms and 1 oxygen ________.

Each oxygen _________ has 2 oxygen ________.

Each hydrogen _________ has 2 hydrogen ________.


Zap that Water!

Session 4


An Analogy for Atoms: Pixels

The smallest piece of a digital photograph is a pixel, short for “picture element.” In a sense, a pixel is like an atom of a digital photograph.

The two illustrations below emphasize this analogy. When you look more and more closely at the digital photograph, the apparent smoothness and continuity of the image becomes grainy. Instead of smooth outlines and blended transitions, you see separate particles of color. Eventually, you come to a pixel of color that is the smallest, most basic part of the image: There’s no such thing as half a pixel as far as a digital image file is concerned.

The second illustration shows that if you were to take smaller and smaller pieces of a sample of gold, you would eventually come to an atom of gold that is the smallest, most basic thing that is still gold. If you were to somehow break a gold atom apart, you would no longer have gold.

TURN AND TALK

Discuss this analogy with a partner. How are pixels and atoms alike? In what ways are they different? What other analogies can you think of to explain the idea of atoms?


Writing

Session 5


Imagine that Aristotle has just been brought to the twenty-first century in a time machine. Remember him? He’s the guy who made everyone think that Democritus’s theory of atoms was silly. Poor Aristotle. He thinks a brownie can be repeatedly divided in half forever, without coming to a smallest piece. He’s in for a bit of shock. Write a letter explaining what you know about atomic theory in modern science. Use the analogy of pixels to explain atomic theory to him, or come up with your own analogy to make the idea of atoms clearer. Try not to hurt his feelings. Aristotle had a lot of interesting ideas and figured out a lot of things, and it’s not his fault he lived centuries before scientific evidence demonstrated the existence of atoms. He might even be excited to learn something new!

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Writing

Session 5


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Writing

Session 5


Wait a second! Isn’t a theory something that we know for sure, knowledge that’s been studied, tested, and proven, like the atomic theory of matter? It’s a serious word, a word that carries weight, right? Researchers study it. Professors teach it. Students are tested on it. Scientifically speaking, that’s true. The dictionary defines “theory” as “a plausible or scientifically acceptable general principle or body of principles offered to explain phenomena.” The germ theory of disease, the cell theory of organisms, and the general theory of relativity are examples of scientific theories that have been built up over time on strong foundations of evidence.

But the word theory has another common meaning that’s nearly opposite! To understand this non scientific definition, let’s turn to the origin of the word. It comes from the Greek theorin, which means “to look at” or “to observe” or “to speculate.” That term comes, in turn, from the Greek theoros, “a spectator,” which comes from thea, meaning “theater.” Perhaps this connection to the theater is part of the reason the word theory is sometimes used to suggest that something not completely real is going on. Unlike the scientific definition, the common definition leaves room for speculation. It implies that something isn’t proven, that it’s just a hunch.

What’s your theory?

Take a look at the following three cartoons:

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The Theory of Theory

ELA

“In theory, I’m supposed to be home by 10 p.m.,” Amari tells his friends, “but

my parents really don’t care what time I get in as long as I remember to lock the front door.” “Okay, so give me your theory,” says

Tanya. “Why do you think Emma bought the exact same jeans and red-striped top as Morgan?”


2

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ELA


Choose one of the cartoons and then ask yourself, what the heck is going on? Don’t limit yourself to only what you see in the cartoon. It’s your theory. Be creative. Now write your theory in a paragraph below.

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ELA


Remember the last time you saw fireworks? Bright colors and huge explosions made an impressive show! But no matter how big and loud the explosions were, no atoms were actually destroyed—they just formed new compounds. That’s because atoms are not destroyed or created in chemical reactions, just rearranged.

In math, you rearrange numbers all the time by using equations. As you perform different operations, the numbers change, but the equation is always balanced. The numbers on the left of the equal sign always equal the numbers on the right. Scientists use chemical equations to show how chemical reactions rearrange atoms. And because atoms aren’t destroyed or created, chemical reactions are always balanced.

Chemical equations use different symbols than math equations, but the idea is the same. Below is the equation for the electrolysis of water (in which electricity separates water into hydrogen gas and oxygen gas).

Two liquid water molecules react to produce 2 molecules of hydrogen gas and 1 molecule of oxygen gas.

2H2O (l) ⟶ 2H2 (g) + O2 (g)

The numbers in front of compound formulas tell you how many molecules of the compound go into the reaction. When no coefficient is written, as with the oxygen molecule, the coefficient is understood to be 1.

The (g) after a compound means it’s a gas. The (l) after a compound means it is a liquid. A solid would be followed by (s).

The arrow in the reaction equation tells you which compounds change into which. It’s like the equal sign (=) in the equation.

The small numbers below and to the right of element symbols tell you how many atoms of each element are in each molecule. These numbers are called “subscripts.” If there’s no subscript after an element symbol, there’s only one atom of that element in the molecule. Which atom in this equation has no subscript?


Balancing Chemical Reaction Equations

Math


Molecules on the left of the arrow are reactants. For this equation, H2O is the reactant.

Molecules on the right of the arrow are products. What are the 2 products for this chemical reaction?

_______________________________ and _________________________________

If chemical equations always need to balance, how do scientists do it? They just count up the atoms! The number of each kind of atom has to be the same on both sides of the arrow.

Is this chemical reaction balanced?

Count the atoms and use the table to record your numbers. The drawing should help, too.

How many... in reactants in products

hydrogen atoms

oxygen atoms

Your Turn!

Does your kitchen stove burn gas or is it electric? Gas stoves burn natural gas, which is a chemical called methane. The chemical formula for methane is CH4.

Here’s the chemical equation for burning methane, but without the coefficients filled in to tell how many of each kind of molecule are in the reaction:

__CH4(g) + __O2(g) ⟶ __CO2(g) + __H2O(g)

What molecules are in the reactants? ________________________________

What molecules are in the products? (You can probably guess what CO2 is.) ____________________________

The equation for burning methane isn’t balanced yet. Can you balance it by filling in the coefficients in front of each reactant and product?

Hint: Although the coefficients are not filled in, all of the subscripts are correct. Some coefficients may be 1, while others may be 2, 3, or perhaps more.



Math

2H2O (l) ⟶ 2H2 (g) + O2 (g)


How many... in reactants in products

carbon atoms

hydrogen atoms

oxygen atoms

Double check your work on the previous page by filling in the table below. Try drawing a diagram of the molecules!

__CH4(g) + __O2(g) ⟶ __CO2(g) + __H2O(g)



Math


What is our world made of? This question has intrigued and confounded philosophers and scientists throughout the ages. They’ve asked, Is the natural world really as varied and complex as it seems? Or are there fundamental substances that everything else is made out of?

Some ancient Greek philosophers imagined that there was just one substance and that everything was some variation of that substance. One philosopher, Thales, believed that water was the first thing to exist and that everything was made from water either condensing, evaporating, or changing its form in some way. Scholars have suggested that the fact that Thales was a man who lived in a wealthy, bustling port town where water was the path to all kinds of success probably influenced his theory.

Anaximenes, another Greek philosopher, also believed that there was just one substance, as Thales did. But Anaximenes thought that substance was air. What made him think this? It appeared to him that air condensed into mist and then rain. He hypothesized that when air condensed further, it formed into earth and then, eventually, stones.

Empedocles, a philosopher who lived in Sicily, is often given credit for coming up with the basic four-element theory, which remained influential in Western thought for the next 2,000 years. He claimed that fire, water, air, and earth were the source of everything in the world. He used the word “root,” instead of “element,” which, most likely, was first introduced by Plato. Empedocles suggested that these four elements combined with each other in different proportions, mixing and separating. And what were the forces that acted on these four elements to unite or divide them? He believed that love and its opposite, strife, which were observable in human relationships, were also at work making constant changes in the natural world.

The theory of the four elements was not limited to Western thought. Buddhists in ancient India believed in the same four basic elements. Their belief was that the elements were made up of units, called paramânu, which had properties, such as movement or solidity. These paramânu supposedly came together in different combinations to make everything in nature. The Chinese also included elements in their worldview, but they had five, not four: fire, water, earth, metal, and wood.

Aristotle, the famous Greek philosopher, added a fifth element, ether, to the original four elements. Based on his observations of the always-changing natural world and his ideas about the characteristics of the four classical elements, he constructed a mental model of the Universe. He imagined four layers of each element, forming the Universe as far as the moon. And beyond the moon? That was the heavenly region, where the invisible ether existed. Unchanging, purer than the other elements, ether, from the Greek word for purity, was something outside the experience of humans.

Discussion:

Clearly, the early thinkers only got part of the story right about what the world is made of. Fast-forward through history and a deeper tale unfolds that brings us to where we are now, with a periodic table that contains well over 100 chemical elements that combine to form millions of compounds. The modern understanding of the chemistry of the elements has allowed people to put together materials that never existed before in nature, and new substances are being discovered and invented all the time.

Our thinking is always influenced by the time and place in which we live. What we’re able to observe in the world around us, what discoveries have already been made, what access we have to which resources—all of this affects how and what we think.

Can you think of a time in which you thought you “knew” something and then discovered later that you didn’t know what you thought you knew?

Examples:

John grew up in a small farming community. He believed that everyone celebrated Christmas, since everyone he knew did. Then he moved to a big city. The people in the apartment across the hall from his family didn’t celebrate Christmas because they were Seventh Day Adventists. His school didn’t have a Christmas party because it was against the rules. His new friend didn’t celebrate Christmas because he was Jewish and celebrated Hanukkah. John had to rethink his assumption that everyone celebrates Christmas.

Serena thought that there were a handful of stars in the night sky, because that’s the most that she’d ever seen. Then she went on her first camping trip, away from the city lights, and was amazed to see how many and how bright the stars were. She realized that she wasn’t right about how many stars are in the sky. She just hadn’t been able to see them!


Elements and Experience

Social Studies

earth water air fire


Scientific or Everyday Use Definition Try using the word...

particle noun

a small piece of matter (often an atom or molecule)

What particle is central to the atomic bomb? How do you know?

particlenoun

a small piece of something How does the size of a beach’s particles of sand affect how the beach feels and looks?

atom noun

the smallest particle of an element

Which atoms combine to form water?

molecule noun

a group of atoms linked together

A molecule of DNA has millions of atoms. Can you think of a molecule comprised of only two atoms?

element noun

a substance that cannot be separated chemically into simpler substances

How many elements on the periodic table can you name?

elementnoun

an essential part of something What are the essential elements of a good essay?

continuous adjective

without interruption Why do you think water appears continuous, even though it is made of separate atoms?

reaction noun

(in chemistry) an interaction between substances that changes the connections between atoms

Why do some chemical reactions produce only one kind of new molecule, while others produce multiple?

reactionnoun

a response to something (often spontaneous)

Describe one situation in which you would trust your immediate reaction, and one that would be smarter to think about first.

compound noun

a substance made of definite proportions of two or more elements

Water is a chemical compound. Can you name the elements that combine to form water molecules?

compoundverb

to put together; to accumulate Can you think of a problem that would be compounded by running late?

compoundadjective

composed of several parts Sunshine and basketball are compound words. What other compound words can you think of?

theory noun

a broad explanation of an aspect of nature, supported by a large, persuasive amount of evidence

How is a scientific theory different from a hypothesis?

theorynoun

a speculation or hunch about something

What’s your theory about the best way to make a new friend?


Examining the Focus Words Closely

Focus Words

SciGen Unit 8.4

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