Click "Print Lesson" button to use your browser print Student Name: Alethea
Date Printed: Jan 11, 2015
Science 3
Unit 6: Physical and Chemical Changes of Matter
Lesson 1: Physical Changes
Duration: Approx. 60 min.
There are one or more assessments in this lesson. Offline assessments and answer keys can be printed from the materials lists. Online assessments must be printed from the assessment itself within the lesson.
Firefox cannot print Flash images. The on-screen images might print as blank spaces. If you need to print this lesson, try using Internet Explorer so that all the images print.
For the Adult
*bowl - salad
*salt - 10mL
*pan
*spoon
*water - 200 mL
*glass, drinking - clear
*heat source
*snack food, trail mix - 1 cup
*crayons 8 - assorted - 16 or more
Investigation: Mixtures
1 day
For this lesson, you will need 1 cup of trail mix and a bowlful of salad to demonstrate that items in mixtures have the same physical properties in or outside of the mixture. Purchase or create mixtures that have a good variety of items that easily can be sorted by type (for example, carrots, cucumbers, lettuce, and grape tomatoes).
Lesson 1: Physical Changes
| physical change | |
| A change in matter from one form to another without becoming a new substance. When water freezes and turns to ice it goes through a physical change, but it is still water. |
| physical property | |
| A characteristic of an object based on its size, shape, color, and state of matter. A physical property of some apples is that they are red. |
Investigation: Mixtures
This lesson involves working with food. Before starting, check with your doctor, if necessary, to find out whether your student will have any allergic reactions.
Investigation: Was That a Physical Change?
Never leave your student unattended near a stove or oven and working with boiling water.
This activity is best completed online.
| Is a mashed apple different than a chunk of apple? It is still an apple--it has just been through a physical change. Experiment with other objects to identify physical changes when the objects are cut, broken, or change phases. | | |
| Objectives
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This activity is best completed online.
| What is a Physical Change? What happens when you boil, chop, or mash something? Does it turn into something else? No, it's just gone through a physical change. It may look different, but it is the same type of matter as before. |
| Everything is made of matter. Solids, such as your cereal bowl and spoon, are made of matter. The orange juice you pour into a glass is mostly liquid matter. Bubbles you blow through the straw are matter in the form of a gas. All matter, whether solid, liquid, or gas, is made out of itty-bitty particles called molecules. Molecules are far too small to see with just your eyes, or normal microscopes. Scientists can observe them with very special devices. Different kinds of molecules stick together to form different kinds of materials. The molecules can break apart and then come together once more in many different ways. It is the kinds of molecules, plus the ways they combine, that give each type of material its properties. | |
| Imagine that someone slices off a piece of an apple and then asks you to describe the piece. You might say the slice is rectangular, white, firm, or sweet smelling. Shape, color, hardness, and odor are all physical properties. Whether something is a solid, liquid, or gas is also a physical property of matter. Look at the photos and describe their physical properties. Look at the objects sitting around you right now, wherever you are. How would you describe the properties of each? | |
| Now, what would happen if you sliced the apple chunk in half to share with a friend? What if you bit it, chopped it, or mashed it up in a bowl? Would it still be an apple? Yes. Your actions might change the apple's shape and size, but they wouldn't change the molecules that make it up. This type of change is called a physical change. When you cut, grind, or bend something you make physical changes in matter. How many other words can you think of that describe physical changes? [1] | |
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Answer(s):
[1]
[1] Answers will vary but may include crush, mash, split, crack, break, or spray.
| Altering the size or shape of matter is making a physical change because the molecules themselves stay the same. An apple is still an apple even if you chop it into tiny pieces. We've already seen another way to cause a physical change as well--you can change the state something is in. What happens to water if you lower the temperature below zero degrees Celsius? [2] What happens to water when you boil it? [3] Ice is still water, even though it has frozen. Water vapor is still water, even though it is now a gas. Changing the state of matter is another kind of physical change. Freezing liquids to solids and boiling liquids to gases are examples of state changes. What are some other ways matter can change states? [4] | |
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Answer(s):
[1]
[2] Water freezes into solid ice.
[3] Water evaporates into water vapor (gas).
[4] Cooling gases often causes them to condense into liquids. Heating solids often causes them to melt into liquids.
[3] Water evaporates into water vapor (gas).
[4] Cooling gases often causes them to condense into liquids. Heating solids often causes them to melt into liquids.
| Bending a gummy worm changes the worm's shape. Cutting a banana changes the banana's size. And melting chocolate to make hot fudge changes the chocolate from solid to liquid--a change in state. All these things are physical changes. Now, what if you scooped ice cream into a dish, added the cut banana, drizzled on hot fudge, and topped it off with gummy worms. What would you get? A banana split is a mixture. Mixtures are made up of two or more different types of matter. When a mixture forms, each part keeps its own properties. The banana is still a banana. It hasn't changed into a gummy worm. And the ice cream won't change into hot fudge, although the two may become mixed together. A mixture is another kind of physical change. | |
| Some physical changes aren’t as easy to see. When you stir salt in water, the salt crystals seem to disappear. But it hasn’t really disappeared. If you tasted the water, you could tell that the salt crystals were still there. The different particles that make up either a mixture or a solution keep their same properties. The molecules that make them up have not changed. That means you can usually separate them back into their original parts. You can spoon the gummy worms out of the banana-split or evaporate the water from salt to leave the crystals behind. The basic particles are still there, and can be recovered. | |
| What would happen if you mixed flour, gravel, sand, and sugar in water? Evaporating Materials will allow you to test those ingredients. Will they completely dissolve? Will the particles return when the water evaporates? Try Evaporating Materials to see more examples of physical changes. |
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This activity is best completed online.
SAFETY: This lesson involves working with food. Before starting, check with your doctor, if necessary, to find out whether your student will have any allergic reactions.
| Mixtures What is a mixture? How is the mixture different than one of the items in the group? Explore the world of mixtures and find out! What happens when you add brown sugar, corn meal, oyster shells, and sesame seeds to water? Try Dissolving Materials to learn more about mixtures. Follow the instructions in your Student Guide to complete this optional activity. |
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This activity is best completed online.
SAFETY: Never leave your student unattended near a stove or oven and working with boiling water.
| Was That a Physical Change? If saltwater is made of water mixed with salt, can it ever be separated into its parts again? Experiment with this solution and find out! Follow the instructions in your Student Guide to complete this optional activity. |
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Answer(s):
[1]
Make a solution of one-half cup water and 3 tablespoons of table salt. Stir it well and pour it into a shallow pan.
Set the pan outside in the sun or leave it in a warm area. Wait for all of the water to evaporate. Depending on where you place the pan this could take anywhere from a few hours to a few days.
Look carefully at the bottom of the pan. What do you see? Wet your finger and rub it on the bottom of the pan. Now lick your finger. How does it taste? What do you think that white residue in the pan was?
Why?
Salt is a solid. Only the water in the ocean or salt water will evaporate. The salt is left behind. This makes the salt water a mixture because we can mix the water and salt together and then easily separate them. The properties of the water and the salt in the pan did not change.
Set the pan outside in the sun or leave it in a warm area. Wait for all of the water to evaporate. Depending on where you place the pan this could take anywhere from a few hours to a few days.
Look carefully at the bottom of the pan. What do you see? Wet your finger and rub it on the bottom of the pan. Now lick your finger. How does it taste? What do you think that white residue in the pan was?
Why?
Salt is a solid. Only the water in the ocean or salt water will evaporate. The salt is left behind. This makes the salt water a mixture because we can mix the water and salt together and then easily separate them. The properties of the water and the salt in the pan did not change.
Lesson Assessment: Physical Changes
This assessment is best completed online, where it will be automatically scored by the computer. If you would like to print it, do so from the assessment itself within the lesson.
Click "Print Lesson" button to use your browser print Student Name: Alethea
Date Printed: Jan 11, 2015
Science 3
Unit 6: Physical and Chemical Changes of Matter
Lesson 2: Chemical Changes
Duration: Approx. 60 min.
There are one or more assessments in this lesson. Offline assessments and answer keys can be printed from the materials lists. Online assessments must be printed from the assessment itself within the lesson.
Firefox cannot print Flash images. The on-screen images might print as blank spaces. If you need to print this lesson, try using Internet Explorer so that all the images print.
For the Adult
*cup, plastic, 8 oz. (2)
*ice - cube
*cylinder, graduated
*paper towels, roll
*household item - baking sheet
*vinegar
*thermometer
*cups - a plastic lid with a hole for a straw (2)
*knife
*steel wool
*spoon, plastic
*baking soda
*celery
Lesson 2: Chemical Changes
| chemical change | |
| A change that results in the formation of one or more new substances. As the iron chair rusted, it went through a chemical change. |
| | molecule [MAH-lih-kyool] |
| The smallest part of a substance that keeps all the properties of the substance and is composed of one or more atoms. The molecules of the sugar mixed with the molecules of the water. |
| substance | |
| Matter that has particular properties. Salt is a substance that dissolves easily in water. |
Investigation: Experiment with Chemical Changes
This lesson involves working with food. Check to find out whether your student will have any allergic reactions to the food. Do not let your student handle the knife.
This activity is best completed online.
| A rusty bike? A toasted marshmallow? A burnt piece of wood? Have these objects gone through chemical or physical changes? Investigate the answers in several experiments. | | |
| Objectives
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This activity is best completed online.
| What Is a Chemical Change? Changing something's size, shape, or state is making a physical change. But sometimes when two kinds of matter come together, their atoms react and make a different substance altogether. These changes are chemical changes. |
| Remember that a physical change alters only the physical properties of something. You can cut a banana, smoosh it, grind it, or roll it into a ball, and it is still banana. These are all physical changes. The banana's molecules--that is, the combinations of atoms tightly stuck together--keep the same properties, even though the banana has changed size or shape. The banana has not become something else, not even if you mix it with apples and oranges. A change of state is also a physical change. Ice melting, molten lava turning into rock, and water vapor condensing on a cold mug are all examples of state changes. Whether it's a solid, liquid, or gas, the water is still water. Just as with other physical changes, a substance remains what it is when it changes states. | |
| Changing something's size, shape, or state is making a physical change. But sometimes when two kinds of matter come together, their atoms react and make a different substance altogether. The atoms break apart and rearrange themselves. This type of change, which results in different molecules, is called a chemical change. When a substance goes through a chemical change, the new substance has different physical properties. It really is a different kind of thing than it was before. For example, an iron nail left outside will rust. The iron reacts with the oxygen in the air to form iron oxide (rust). The rust is made of iron atoms and oxygen atoms put together. Rust is red, solid, and flaky. Those are different physical properties than those of either oxygen (a colorless gas) or iron (a hard, gray metal). | |
| Suppose you sat down to dinner and were served a burning metal and a poisonous green gas. Would you ever go back to that restaurant? Salt is another good example of something that has gone through a chemical change. The scientific name for the salt we put on food is sodium chloride. It's made from two different types of atoms--sodium and chlorine. By itself, sodium is a soft metal that bursts into flame when mixed with water. And chlorine is a poisonous gas. But when you combine sodium with chlorine gas, sodium chloride (table salt) forms. The salt has its own physical properties, different from those of the sodium or the chlorine. It's much more than a physical change. The chemical reaction has actually made new, and tasty, particles. | |
| Sometimes a physical change causes a chemical change. Cut a slice off an apple. That's a physical change. Now leave the slice out for a while. What happens? It turns brown--evidence of a chemical change. The substances in the apple slowly react with the oxygen in the air. The change in the apple's color tells you that a chemical change is taking place. When something burns, it also goes through a chemical change. As wood burns, the molecules of the wood react with oxygen in the air to make the wood turn black, and then come apart as gas and smoke, leaving only a little ash behind. The heat and light from the flames, along with the color and other changes in the wood, is a hint that a chemical change is taking place. | |
| Light, heat, and changing color are all signs of a chemical change. Some chemical changes can happen quickly, such as when wood burns. Other chemical changes are slower, such as when an iron nail rusts. But all chemical changes either absorb or give off energy, in the form of heat and light. You can often tell if energy is being absorbed or given off by watching the temperature of the stuff in the reaction. Study the photo of the cookies. What changes were caused by baking them? A good way to tell a chemical change from a physical change is to ask yourself if the new substance can easily be changed back to the old one. There's no way you can take a baked cookie and turn it back into cookie dough. That's because baking raw cookie dough in a very hot oven actually changes the dough in a chemical way. | |
| Atoms break apart and recombine in many different ways. Although the molecules that form from the combinations may be different, the underlying atoms stay the same. Chemical changes are rearrangements of atoms into different molecules, not changes in the atoms themselves. Still, once a chemical change has taken place, it's hard to change it back. You can't make rust back into nails without putting it through another chemical change. You can remember that physical changes are described with words such as cutting, grinding, melting, evaporating, and squashing. Chemical changes involve words such as burning, rusting, cooking, coloring, and exploding! | |
This activity is best completed online.
SAFETY: This lesson involves working with food. Check to find out whether your student will have any allergic reactions to the food. Do not let your student handle the knife.
| How is a chemical change different from a physical change? Experiment and observe to find evidence of physical and chemical changes. Follow the instructions in your Student Guide to complete this optional activity. |
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Lesson Assessment: Chemical Changes
Print this offline assessment and answer key using the links below. You will need to enter your student's results online later.
Click "Print Lesson" button to use your browser print Student Name: Alethea
Date Printed: Jan 11, 2015
Science 3
Unit 6: Physical and Chemical Changes of Matter
Lesson 3: Atoms
Duration: Approx. 60 min.
There are one or more assessments in this lesson. Offline assessments and answer keys can be printed from the materials lists. Online assessments must be printed from the assessment itself within the lesson.
Firefox cannot print Flash images. The on-screen images might print as blank spaces. If you need to print this lesson, try using Internet Explorer so that all the images print.
For the Adult
*toothpick (8)
*grapes - purple (8)
*plastic wrap, clear
*clay, oil-based modeling - 2 colors
*grapes - green (8)
*pea, green (8)
Investigation: Make a Model Atom
1 day
If you don't already have them, you will need large green grapes, large purple grapes, and green peas for the Make a Model Atom activity in this lesson.
Lesson 3: Atoms
| atom | |
| A tiny particle that is the fundamental building block of substances. The properties of the atom determine the properties of the element made up only of those atoms. |
| | compound [KAHM-pownd] |
| A substance containing atoms of two or more elements. Water is a compound of hydrogen and oxygen. |
| electron | |
| A tiny part of an atom with a negative electric charge. In an atom, electrons form a cloud around the nucleus. |
| | molecule [MAH-lih-kyool] |
| The smallest bit into which a chemical substance can be divided and still have the properties of that substance. Molecules of water contain hydrogen and oxygen atoms. |
| neutron | |
| A particle in the nucleus of an atom, which has no electric charge. Atoms contain neutrons, electrons, and protons. |
| | nucleus [NOO-klee-uhs] |
| The core of an atom made up of protons and neutrons. Electrons form a cloud around the nucleus of an atom. |
| proton | |
| A tiny part of the nucleus of an atom, which has a positive electric charge. The number of protons determines the chemical properties of the atom. |
This activity is best completed online.
| Atoms? Molecules? How are they all related to make up matter? Build two models to discover the microscopic world of the atom. | | |
| Objectives
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This activity is best completed online.
| Atoms: Building Blocks of All Matter What is an atom? What do atoms have to do with elements? Find out how these tiny particles make up everything that you can see, touch, and smell, and even some things you can't! |
| You know that changing something's size, shape, or state is called a physical change. When you cut up a log, build a tower out of playing cards, or freeze juice to make ice pops, you are making physical changes. You also know that sometimes molecules break apart and recombine into new molecules through chemical reactions. New substances are made during these chemical changes. Iron reacts with oxygen in the air and turns into rust. Sodium metal and chlorine gas combine with the release of a lot of energy to form ordinary table salt (sodium chloride). Wood, when it burns, combines its molecules with oxygen and breaks apart. These new substances often have very different properties than the substances from which they came. | |
| Atoms are the building blocks of molecules. Substances that have only one type of atom--such as sodium metal, chlorine gas, gold, oxygen, and hydrogen--are called elements. All of an element's atoms are of the same kind. All sodium atoms, for example, have the same number of protons and electrons, and they have all the same properties. Chlorine atoms all have the same number of protons and electrons too, but this number is different from sodium atoms. You can separate sodium chloride (table salt) into two different atoms--sodium and chlorine-- using chemical reactions. Sodium chloride is a compound. A compound is made up of more than one type of atom. Water is another example of a compound. Water is made up of hydrogen atoms and oxygen atoms. Hydrogen and oxygen are gases as part of our atmosphere, but when you put them together you get a very splashy compound! | |
| In ancient times, people thought everything on Earth was made of just four elements: earth, air, fire, and water. We now know these people were wrong. None of these is an element. Instead, there are more than a hundred different elements, and they combine to form many compounds. You can think of atoms as the "building blocks" of matter. That's because all matter, from bean sprouts to a horse's nose, is made of atoms in one combination or another. But you still can't see individual atoms--they're much too small. How did scientists find out anything about atoms without being able to see atoms until very recently with special instruments? It took a very long time and plenty of careful experiments. And we still don't have it all figured out. | |
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| During chemical reactions, atoms come apart and join back together in different ways. But we can't change atoms of one element into atoms of another element--at least not in a chemical reaction. People once dreamed of using chemical reactions to turn lead into gold to become instantly rich. Now we know it takes the enormous temperatures and pressures of the sun's core, or the center of a nuclear reactor, to change one element into another--definitely not a tabletop experiment, and too expensive to change lead into gold! A man named John Dalton worked on the idea that matter was made up of tiny building blocks, which he called atoms. He suggested that some stuff was made up of just one kind of atom (an element), while other stuff was made up of combinations of atoms. We now know that atoms themselves are made up of even smaller pieces, but Dalton’s discoveries still hold true. An element’s chemical properties are determined by what atoms make it up and how they are arranged. | |
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| Scientists have found that atoms are made up of three main parts: protons, electrons, and neutrons. Atoms of different elements just have more, or fewer, protons and electrons--it's these two that make atoms different from each other. For example, a hydrogen atom has one proton and one electron; it may have zero, one, or two neutrons. An oxygen atom has eight protons, eight electrons, and eight, nine, or ten neutrons. The more protons and neutrons an atom has, the greater the atom's mass. It may seem funny to talk about the mass of an atom when atoms are so small. But atoms of different elements don't have the same mass. Which do you think has greater mass, a hydrogen atom or an oxygen atom? [1] A simple way to think about an atom is this. At the center of an atom is the nucleus. The nucleus contains the protons and the neutrons. Surrounding the nucleus is a cloud of electrons. When two atoms react chemically, they swap electrons or rearrange their electron clouds. | |
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Answer(s):
[1]
[1] An atom of oxygen has greater mass.
[2]
Atomic structure is far more complicated than this simplified model, and your student may see atoms represented in a variety of ways. This model should provide a good starting point for your student to begin understanding the parts of an atom.
This activity is best completed online.
| Make a Model Atom What is an atom made of? Make a model to learn about the parts of an atom. Follow the instructions in your Student Guide to complete this optional activity. |
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This activity is best completed online.
| Make a Model Water Molecule How is an atom different from a molecule? Build on your understanding of an atom to create a molecule of water. Follow the instructions in your Student Guide to complete this optional activity. |
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Lesson Assessment: Atoms
This assessment is best completed online, where it will be automatically scored by the computer. If you would like to print it, do so from the assessment itself within the lesson.
Click "Print Lesson" button to use your browser print Student Name: Alethea
Date Printed: Jan 11, 2015
Science 3
Unit 6: Physical and Chemical Changes of Matter
Lesson 4: Mendeleev and the Periodic Table
Duration: Approx. 60 min.
There are one or more assessments in this lesson. Offline assessments and answer keys can be printed from the materials lists. Online assessments must be printed from the assessment itself within the lesson.
Firefox cannot print Flash images. The on-screen images might print as blank spaces. If you need to print this lesson, try using Internet Explorer so that all the images print.
Lesson 4: Mendeleev and the Periodic Table
| atom | |
| The smallest part of an element that affects its chemical behavior. Atoms make up molecules. |
| | Dimitry Mendeleev [dih-MEE-tree men-duh-LAY-uhf] |
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| | Jons Jacob Berzilius [youns YAH-kawp buhr-ZAY-lee-uhs] |
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| periodic table | |
| An organized chart of all known elements. Mendeleev organized elements into the periodic table. |
Beyond The Lesson: The Periodic Table Comes Alive
As always, you may wish to preview any websites before your student views them.
This activity is best completed online.
| How many elements have scientists discovered? How are the elements organized? Explore the Periodic Table of the Elements to discover patterns and relationships between elements. | | |
| Objectives
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This activity is best completed online.
| The Periodic Table of the Elements Let's explore the Periodic Table of the Elements and understand its origin, what it represents, and how it is organized. |
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| John Dalton showed that compounds, such as water or sodium chloride, are all made up of atoms of more than one type of element. He suggested that the atoms of one element are all alike. By the mid-1800s, shortly after Dalton's time, chemists had discovered almost 70 elements. They found these elements by breaking down materials. When they found a substance that could not be broken down into simpler materials by various chemical reactions, they called it an element. | |
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| When you pick up your room, where do you put the toys? Maybe you put all the stuffed animals on the bed, or all the electronic games in a basket. As scientists began discovering more and more elements, they realized they needed a way to organize everything, just as you need a way to organize your toys. How could the scientists “pick up” their lab data and put it in useful baskets? |
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| The first step toward organizing elements was when a Swedish chemist named Jons Jacob Berzilius gave each known element a letter symbol to go along with its name. Chemists around the world still use these symbols today. | | |
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| Using symbols helped, but the chemists hoped they would find some basic order in nature itself. As time went on, they slowly began seeing a pattern. Although each element has its own properties, some groups of elements seemed to have similar properties. For example, some elements are gases and others are solid metals. Some elements combine easily, while others do not. Was this a hint about how to organize the elements--or just more clutter? Can you think of some good ways to organize information into groups? | |
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| Things finally came together in 1871 when Russian scientist Dimitry Mendeleev put all the elements in a table. Mendeleev saw that the properties of the elements were periodic--that is, they had a repeating pattern. The elements in each row of the table increase in mass from left to right and top to bottom. Groups of elements in columns all have similar properties, and are called groups (or sometimes families). These elements resemble each other, sort of how members of your family resemble each other. They are similar because they react with other elements in similar ways. | |
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| Mendeleev actually predicted the existence of elements that had not been discovered! He left blank spaces for those elements, and he was right. Soon, the first of the missing elements was discovered and named gallium. Gallium's properties put it on the table exactly where he predicted. | |
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| We still use Mendeleev's table today. The modern version of the Periodic Table of the Elements is a chart of all known elements. Most of the elements on the chart occur in nature, but some are created in laboratories. Each element has its own square, which also shows its name and symbol. Compounds do not appear on the table, just the elements that make up compounds. Water and sodium chloride are compounds, so you won't see them. But what about the elements hydrogen and oxygen? Can you find sodium and chlorine? | |
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| The periodic table helps explain the properties of the elements. Elements are the basic building blocks of all matter. But it's actually compounds that make up the huge number of different materials around us. Even a simple log fire makes all sorts of chemical compounds, each with different properties. Most of these are just various compounds of carbon, oxygen, nitrogen, and hydrogen, but there are many possibilities with quite different properties. Compounds show us the complexity of nature, while elements show its basic simplicity. | |
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This activity is best completed online.
| Learn Your Way Around the Periodic Table How are elements organized within the periodic table? Explore the periodic table to find out! Follow the instructions in your Student Guide to complete this optional activity. |
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Lesson Assessment: Mendeleev and the Periodic Table
Print this offline assessment and answer key using the links below. You will need to enter your student's results online later.
This activity is best completed online.
SAFETY: As always, you may wish to preview any websites before your student views them.
| The Periodic Table Comes Alive What do the different elements look like? How do you pronounce the names of the elements? Explore this site to find out more about each element. Choose an element to learn more about it. You can even hear its name pronounced! |
Click "Print Lesson" button to use your browser print Student Name: Alethea
Date Printed: Jan 11, 2015
Science 3
Unit 6: Physical and Chemical Changes of Matter
Lesson 5: Physical and Chemical Changes of Matter Unit Review
Duration: Approx. 60 min.
There are one or more assessments in this lesson. Offline assessments and answer keys can be printed from the materials lists. Online assessments must be printed from the assessment itself within the lesson.
Firefox cannot print Flash images. The on-screen images might print as blank spaces. If you need to print this lesson, try using Internet Explorer so that all the images print.
For the Adult
*gum drops - 3 different colors
*heat source
*pan
*knife
*plastic wrap, clear
*toothpick (5)
*butter, stick
Unit Review: Hands-On Review
Keep child away from the stove when in use.
This activity is best completed online.
| Review and demonstrate what you have learned about physical and chemical changes. | | |
| Objectives
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This activity is best completed online.
| Unit Review Let's review what you have learned in the previous lessons about properties of matter, physical and chemical changes, atoms, and the Periodic Table of the Elements. |
| Everything is made of matter. All matter, whether solid, liquid, or gas, is made out of molecules. Physical properties can be used to describe matter. Shape, color, hardness, and size are all physical properties. The state of matter--whether something is a solid, liquid, or gas--is also a physical property. A physical change can alter an object's size, shape, or state. In a physical change, the molecules that make up the object themselves don't change. A physical change alters only the physical properties of matter. Cutting, grinding, bending, or mashing something causes a change in size or shape. Boiling, freezing, condensing, or melting matter causes a change in state. Making a mixture is another kind of physical change - the molecules stay the same, they are just mixed together. | |
| When substances go through a chemical change, they form new substances with different physical properties. For example, a log fire causes many chemical changes that turn wood molecules and oxygen into new molecules. Some of these are gases, such as carbon dioxide, while others are different kinds of matter, such as charcoal. Many are different combinations of carbon, oxygen, and hydrogen atoms. All chemical changes either give off energy, such as heat or light, or absorb energy. Once a chemical change has taken place and something new has formed, it requires quite different operations to reverse the change. In order to change charcoal back to wood, another chemical change would have to take place, if it could be done at all. Light or heat production, cooling, color changes, and formation of a new solid are all evidence of a chemical change. | |
| Protons, electrons, and neutrons make up atoms. The tiny center of an atom is called the nucleus. The protons and the neutrons are found in the nucleus. Surrounding the nucleus is a cloud of electrons. Different numbers of protons, electrons, and neutrons form different types of atoms. In ancient times, people thought that everything on Earth was made of just four elements: earth, air, fire, and water. We now know that none of these things are elements. There are about 100 true elements, each with their own physical properties. We can think of elements as the "building blocks" of all matter. The English chemist John Dalton was the first modern scientist to use the term atoms. Dalton suggested that each compound is made up of fixed numbers of atoms of different elements combined together - the start of modern atomic chemistry. | |
| Substances are made of molecules. Molecules are made of atoms. Substances that have only one type of atom, such as sodium metal, chlorine gas, gold metal, liquid mercury, oxygen gas, and hydrogen gas, are called elements. The atoms that make up elements cannot be separated further into other kinds of chemical substances. They can combine, however, to form compounds. Compounds, such as water or sodium chloride, are made up of atoms of more than one element. When compounds are formed during chemical reactions, atoms are separated and rejoined in different combinations. But atoms of most elements cannot change into atoms of another element by chemical means. To do so requires huge amounts of energy, with conditions like those at the center of the Sun or inside a nuclear reactor. | |
| Swedish chemist Jons Jakob Berzelius gave each element a letter symbol to go along with its name. Chemists worldwide still use these symbols today as a type of shorthand. The first letter of an atomic symbol is always capitalized. The second letter is always lower case. In 1869 the Russian scientist Dimitry Mendeleev organized all the elements into the first periodic table. We still use a version of his table today, called the Periodic Table of the Elements. It is an organized chart of all known elements. Each element is placed in its own square on the table along with its symbol. | |
This activity is best completed online.
SAFETY: Keep child away from the stove when in use.
| Hands-On Review Let's review the material of the unit with three mini-activities. Print the Periodic Table of Elements if you have not already done so. Follow the directions in your Student Guide to complete this activity. |
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Unit Assessment: Physical and Chemical Changes of Matter
Print this offline assessment and answer key using the links below. You will need to enter your student's results online later.
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