CHEMICAL REACTIONS!
Dr. Susan Berk Koch Illustrated by Micah Rauch
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CONTENTS Timeline . . . iv Periodic Table of Elements . . . vi Introduction . . . 1 Chemistry Matters! Chapter 1 . . . 11 Mixtures: Be a Detective Chapter 2 . . . 25 Abracadabra: Chemical Reactions Chapter 3 . . . 41 Water, Acids, and Bases Chapter 4 . . . 56 It’s a Gas! Chapter 5 . . . 68 Manmade Compounds Glossary * Metric Conversions Resources * Essential Questions * Index
Interested in primary sources? Look for this icon. Use a smartphone or tablet app to scan the QR code and explore more! Photos are also primary sources because a photograph takes a picture at the moment something happens. You can find a list of URLs on the Resources page. If the QR code doesn’t work, try searching the internet with the Keyword Prompts to find other helpful sources.
EXPLORE CHEMICAL REACTIONS
CHEMICAL REACTIONS! 1803:
Chemist John Dalton publishes his atomic theory, which states that all matter is composed of atoms, which are small and indivisible. The Greeks had many of these ideas and Dalton built on them.
300 BCE:
Ancient Greek philosopher Aristotle declares the existence of only four elements: fire, air, water, and earth. He says, mistakenly, that all matter is made up of these four elements.
430 BCE:
1789: Chemist Antoine Lavoisier
shows that the mass of products in a reaction is equal to the mass of the reactants. In other words, no mass is lost in a chemical reaction. This became known as the law of conservation of mass. It is one of the most important and basic laws of modern chemistry and physics.
Democritus, an ancient Greek philosopher, proclaims the atom to be the simplest unit of matter.
1649:
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German pharmacist Hennig Brand discovers the element phosphorous. Elements such as gold, silver, tin, copper, lead, and mercury had been known for a long time, but this was the first scientific discovery of an element.
TIMELINE 1869:
Russian chemist Dmitri Mendeleev creates the first periodic table by grouping together elements that act alike. The gaps in his table are where undiscovered elements will fit in later.
2020:
Emmanuelle Charpentier and Jennifer A. Doudna win a Nobel Prize in chemistry for the development of a method of gene editing that might help treat certain diseases.
1890s–1900s:
Marie and Pierre Curie discover radioactive materials and two new elements. They win a Nobel Prize in 1903 and Marie wins a second one in 1911. She is the first woman to win a Nobel Prize and the first person to win two Nobel Prizes!
2017:
Three scientists develop a method to see the three-dimensional structure of cells on an atomic level, paving the way for new medicines and therapies.
1938:
1932:
The first nuclear fusion reaction is performed in a laboratory. This process involves smashing together two or more smaller elements to form a heavier element. Every star in the universe, including the sun, uses nuclear fusion to produce energy.
German chemists Otto Hahn and Lise Meitner discover nuclear fission when large uranium atoms are split apart. Today, nuclear fission is used to generate 10 percent of the world’s electricity.
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CHEMICAL REACTIONS!
vi
PERIODIC TABLE OF ELEMENTS
vii
INTRODUCTION
CHEMISTRY MATTERS! You might think chemistry happens only in a laboratory with people wearing white coats. Not true! Chemistry is all around us! We come across chemical reactions every day. Did you eat toast this morning? That toast was a result of a chemical reaction. Did you wash your hands before you ate your toast? Soap cleans because of a chemical reaction, too! There’s even chemistry happening inside your own body as you break down the food you eat into nutrients .
Chemistry is the science of change and it always happens for a reason. People have been trying to discover those reasons for centuries.
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INVESTIGATE
Where can you see chemistry happening right now?
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CHEMICAL REACTIONS! chemistry: the science of how atoms and molecules combine to
form substances and how those substances interact, combine, and change.
atom: the smallest particle of
an element. Atoms are the tiny building blocks that make up everything in the universe.
molecule: a group of atoms bound
together to form a new substance. An example is water (H2O), which is two hydrogen atoms and one oxygen atom.
chemical reaction: the combination of two or more substances that results in a completely new chemical substance. This can also mean the chemical breakdown of one substance into its parts.
nutrients: substances in food and soil that living things need to live and grow. substance: the material that
something is made of.
alchemist: a person who practiced an early form of chemistry with the goal of turning ordinary metals into gold. theory: a set of ideas based on
observation and data to explain something that has happened.
CHEMISTRY HISTORY Scientists who specialize in chemistry are called chemists. The first chemists date back to ancient times, but they weren’t called chemists. They weren’t even scientists! They were just people who wondered, “What happens if I put potatoes into a fire?” or “Why is a cooked egg different from a raw egg? These people were simply curious. They wanted to know what might happen if they mixed different substances to make something new.
Alchemists were some of the first
thinkers who experimented with chemical reactions. Their goal? To change regular metal into gold! No one ever succeeded at this, but these people learned more and more about the science of chemistry.
As people became better at recording their observations and measurements, WORDS TO KNOW scientists did experiments to find out more about the world we live in. As the tools and techniques that chemists used improved, scientists could develop even more accurate theories about how our world works.
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Chemistry Matters! matter: anything that has
Today, chemists still study matter. They still ask questions about how matter is put together, how it changes, and why it sometimes doesn’t change at all. They ask what’s happening when matter fizzes, explodes, or changes color! Chemistry is called a central science because matter is all around us.
weight and takes up space. Almost everything is made of matter!
gas: a substance in which atoms and molecules are spread far apart.
element: a pure substance that contains only one kind of atom.
WORDS
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MATTER MATTERS!
Everything you see right now is made of matter. A fern, a ham sandwich, and the moon. Your dog, the milk you drank for lunch, and the carton it came in are also made of matter. Even the air you’re breathing is made of matter. Matter is anything that DID YOU KNOW? takes up space and has mass. We Hydrogen, a gas, is the are made of matter, but what is most common element. Hydrogen forms part of every matter made of? living thing on our planet!
HAVE YOU EVER COOKED AN EGG? THAT’S A CHEMICAL REACTION!
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CHEMICAL REACTIONS! property: a characteristic of
something. The way something looks or behaves.
particle: a tiny piece of matter.
WORDS
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Matter is made of atoms. Atoms are the building blocks for all matter and are too tiny to see. In fact, millions of atoms would fit in the period at the end of this sentence.
ing ! Th
e ve ey m ake up
ROBERT BOYLE SETS THE RECORD STRAIGHT
People used to think that there were only four elements: fire, air, water, and earth. They thought this was true for more than 2,000 years. In 1661, a chemist named Robert Boyle (1627–1691) challenged this idea. He performed many different experiments that showed there were more than just the four different elements. He also helped show that matter was made up of tiny particles that behave differently at different times. He proved that gases are small particles surrounded by space.
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th
Different elements behave in different ways. Gold doesn’t make a balloon float and you can’t wear helium around your neck! Instead, all the elements have different properties .
WHY CA
N
? MS O
Y
Have you ever played with a balloon filled with helium? Do you know anyone who wears gold jewelry? Both helium and gold are special kinds of matter. They are elements! An element is a pure substance made of just one kind of atom. All atoms in gold are gold atoms. All atoms in ER TRUS NE V TA U helium are helium atoms. Elements combine T O together in different ways to make up all the matter in the world.
ry
Chemistry Matters! periodic table: a chart that shows the chemical elements arranged according to their properties.
All 118 elements are important in the study of chemical reactions. How do chemists keep track of all these elements?
symbol: an image or character that stands for something else.
WORDS
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THE PERIODIC TABLE
The periodic table is a chart that lists all the known elements. Some of these elements are found only in laboratories and are made by scientists. Ninety-eight of them are DID YOU KNOW? found in nature. Scientists are still
On the periodic table, each element has a number, a name, and a symbol . Each element has its own box with the element’s name, its symbol, and how heavy it is.
discovering new elements! In 2016, four new elements were added to the periodic table. You can learn more about elements in this interactive chart.
I NTERACTIVE PERIODIC TABLE KIDS
ATOMIC NUMBER SYMBOL
ATOMIC WEIGHT
NAME
As you can see from the chart, H is for hydrogen and O is for oxygen.
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CHEMICAL REACTIONS! solid: one of the states of
matter where the particles are bound tightly and do not move much. This book is a solid.
WORDS
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But . . . what about iron? The symbol for iron is Fe. That doesn’t make sense—unless you know that the Latin name for iron is ferrum! That’s where the Fe comes from.
The ways elements look or behave are called their properties. Their weight, color, and the temperature at which they melt are all examples of properties. Elements on the periodic table are grouped by their properties. Think of the elements as a kind of alphabet. The English alphabet has 26 letters. These letters combine to make all the English words we use. The 118 elements on the periodic table join to make everything on Earth!
DID YOU KNOW?
One property of solids is that they hold their shape. Iron is a solid. Gold is a solid, too. Iron and gold share that property.
MAKING THE TABLE In 1869, Russian chemist Dmitri Mendeleev (1834–1907) created the first periodic table. Many elements were being discovered back then and it was getting hard to keep them straight. Mendeleev thought elements that acted alike could be grouped together. He made a grid of the elements, but to make it work, he had to leave gaps. He realized that the gaps were where undiscovered elements could fit later. His predictions were right! Today, all the gaps have been filled. Element 101, Mendelevium, is named after him.
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Chemistry Matters! attract: when an invisible
force pulls things together.
WHEN ELEMENTS GET TOGETHER If elements make up everything in the world, how do they know what to combine into? Broccoli? Cat? Car? They follow instructions! Here’s how it works.
bond: to stick together. compound: a substance
made of two or more elements.
formula: the use of symbols to represent the elements in a substance. subscript: the small number that tells how many atoms there are of each element.
Sometimes, the elements are attracted to each other, just like magnets are attracted to each other. The elements WORDS TO KNOW want to stick together. When two or more elements bond together, they form a compound . Once a compound is formed, it can’t come apart by itself. Every compound has an exact recipe, called a formula . The formula shows the symbols of each element that HYDROGEN combined to make the compound. The formula also has small numbers called subscripts to show how many atoms there are of each element. We are all familiar with the compound water. One molecule of OXYGEN water is made from one oxygen atom and two hydrogen atoms. Its formula is H2O. H is the symbol for hydrogen. The symbol for oxygen is O. The subscript 2 shows that there are two atoms of hydrogen bonded to a single atom of oxygen. When there is only one atom of an element in a formula, no number is written.
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CHEMICAL REACTIONS! liquid: one of the three
states of matter. The particles in a liquid cluster together and flow. A liquid takes the shape of its container.
preserve: to store food in a way that protects it from rotting.
evaporate: to change
from a liquid to a gas.
WORDS
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Learn more about amazing water! How is water different from most of the other elements on Earth?
NBC LEARN MOLECULE WATER
The formula for a compound does not change. Water will always have two hydrogen atoms and one oxygen atom. That’s why people sometimes refer to water as “H two O.”
New compounds have different properties from the elements that bonded to create them. Oxygen is a gas in the air. So is hydrogen. These two gases bond and form a liquid —water! The way water behaves is very different from the way oxygen and hydrogen behave.
DID YOU KNOW?
We have more than 40 elements in our bodies. But 97 percent of our bodies is made of only five elements: oxygen, carbon, hydrogen, nitrogen, and calcium.
WHITE GOLD Do you put salt on your baked potato? Salt is another compound! The formula for salt is NaCl. Salt has one atom of sodium (Na) and one atom of chloride (Cl). Before refrigerators, people used salt to preserve foods. Egyptians used salt to preserve mummies! Salt wasn’t always as easy to find as it is today. Salt could be found in some rocks. Salt could only be produced by evaporating sea water. In ancient Greece, slaves were sold for salt! And during the War of 1812, the American government paid their soldiers in salt. The soldiers were happy to have the hard-to-find compound that made their food taste better.
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Chemistry Matters! Did you know that chemical reactions are part of erupting volcanoes? And a chemical reaction is why the cut apple you left on the counter turned brown. Chemical reactions are everywhere! In this book, we’ll turn into chemistry detectives to solve the mystery of what makes a reaction. Ready? Let’s go!
GOOD SCIENCE PRACTICES
Every good scientist keeps a science journal! Choose a notebook to use as your science journal. Write down your ideas, observations, and comparisons as you read this book. For each project in this book, make and use a scientific method worksheet, like the one shown here. Scientists use the scientific Scientific Method Worksheet method to keep their Question: What are we trying to find out? experiments organized. A What problem are we trying to solve? scientific method worksheet Research: What information will help you keep track of your is already known? observations and results. Hypothesis/Prediction: What do Each chapter of this book begins I think the answer will be? with a question to help guide your exploration of chemistry. Keep the Equipment: What supplies do I need? question in your mind as you read the chapter. Record your thoughts, Method: What steps will I follow? questions, and observations in your science journal. At the end of each Results: What happened? Why? chapter, use your science journal to record your thoughts and answers. Does your answer change INVESTIGATE! as you read the chapter?
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Where can you see chemistry happening right now?
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SUPPLIES
PROJECT! EAT A WATER MOLECULE
* toothpick * 1 grape * 2 blueberries
We now know what the formula for water looks like. What does an actual molecule of water look like? How can we see something that small? Powerful X-ray machinery allows scientists to predict how the atoms in a molecule look. Let’s build a model so we can see, too.
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Break a toothpick in half and press one half into the grape, leaving part of it showing.
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Attach a blueberry to the other side of the toothpick.
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Put the other toothpick half in the grape. Arrange the toothpicks the way a cat’s ears would be.
DID YOU KNOW? Water is the most abundant compound on Earth! Notice how the most common element, hydrogen, is needed to form water.
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Put the other blueberry on that toothpick. You’ve made an edible model of a water molecule! The toothpicks are holding your fruit together the way a bond holds atoms. Remember that bonds act like magnets. The bonds hold the hydrogen and oxygen atoms together, forming a molecule of water!
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In your science notebook, draw the process of two hydrogen atoms bonding with an oxygen atom. What predictions can you make based on your drawing? What might a drawing of a salt molecule look like?
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You can eat your water molecule model, but be careful not to eat the toothpick!
WORDS
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X-ray: a powerful wave of
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energy that lets doctors see bones inside bodies.
Think About It! What other fruits or vegetables could you use to make a water molecule? When you choose, remember that an oxygen atom is larger than a hydrogen atom.