High School Chemistry/Matter

We are all familiar with matter. The definition of matter is anything that has mass and volume (takes up space). For most common objects that we deal with every day, it is fairly simple to demonstrate that they have mass and take up space. You might be able to imagine, however, the difficulty for people several hundred years ago to demonstrate that air has mass and volume. Air (and all other gases) are invisible to the eye, have very small masses compared to equal amounts of solids and liquids, and are quite easy to compress (change volume). Without sensitive equipment, it would have been difficult to convince people that gases are matter. Today, we can measure the mass of a small balloon when it is deflated and then blow it up, tie it off, and measure its mass again to detect the additional mass due to the air inside. The mass of air, under room conditions, that occupies a one quart jar is approximately 0.0002 pounds. This small amount of mass would have been difficult to measure in times before balances were designed to accurately measure very small masses. Later, scientists were able to compress gases into such a small volume that the gases turned into liquids, which made it clear that gases are matter.

On the other hand, when you add heat to an object, the temperature of the object increases, but even the most sensitive balance cannot detect any difference in mass between an object when cold and when hot. Heat does not qualify as matter.

Lesson Objectives

• Define matter and explain how it is composed of building blocks known as "atoms".
• Distinguish between mass and weight.

The Material in the Universe

Knowing that planets, solar systems, and even galaxies are made out of matter doesn't bring us any closer to understanding what matter is. Up until the early 1800s, people didn't really understand matter at all. They knew that there were "things" in the world that they could pick up and use, and that some of these "things" could be turned into other "things". For example, someone who found a piece of copper could shape it into a necklace or melt it together with zinc to make brass. What people didn't know, though, was how all of these "things" were related. If they had, the alchemists probably wouldn’t have wasted so much time trying to convert common metals into gold. You’ll understand why by the time you're finished with this section. Even though the universe consists of "things" as wildly different as ants and galaxies, the matter that makes up all of these "things" is composed of a very limited number of building blocks (Figure 1.18).

Figure 1.18: Everything from an ant to an entire galaxy is composed of matter.

These building blocks are known as atoms, and so far, scientists have discovered or created a grand total of 118 different types of atoms. Scientists have given a name to each different type of atom. A substance that is composed of only one type of atom is called an element. Each element, therefore, has its own name; it also has its own symbol. The "periodic table" is a way of summarizing all of the different atoms that scientists have discovered (Figure 1.19). Each square in the periodic table contains the symbol (a capital letter or a capital letter followed by a lower case letter) for one of the elements.

Figure 1.19: The Periodic Table

At this point, what should amaze you is that all forms of matter in our universe are made with only 118 different building blocks. In some ways, it's sort of like cooking a gourmet, five-course meal using only three ingredients! How is it possible? To answer that question, you have to understand the ways in which different elements are put together to form matter.

The most important method that nature uses to organize atoms into matter is the formation of molecules. Molecules are groups of two or more atoms that have been bonded together. There are millions of different ways to bond atoms together, which means that there are millions of different possible molecules. Each of these molecules has its own set of chemical properties, and it's these properties with which chemists are most concerned. You will learn a lot more about atoms and molecules, including how they were discovered, in a later part of the textbook. Figure 1.20, however, gives you a preview of some of the common molecules that you might come in contact with on a daily basis.

Figure 1.20: Some common molecules and the atoms that they are made from.

Now back to the question of why alchemists had trouble making gold out of other common metals. Most naturally occurring metals, including gold, iron, copper, and silver are elements. Look carefully at the Periodic Table in Figure 1.19. Do you see the symbol Au? Au is the symbol for gold. Gold is one of the 118 different types of atoms – it's one of nature's building blocks. Take another look at the Periodic Table. Do you see the symbol Fe? Fe is the symbol for iron. Again, that means that iron is an element, or a type of atom. In fact, copper (Cu), tin (Sn), and silver (Ag) are all elements. In other words, alchemists were trying to convert one type of element, or building block, into another type of element, and that just can't be done by chemical means.

Chemical reactions can turn elements into molecules, molecules into other molecules, and molecules back into elements. Chemical reactions cannot, however, turn one type of element into another type of element. The only way to do that is through what are known as nuclear reactions, and nuclear reactions require advanced technical equipment that wasn't around in the days of the alchemists. It's like building a house. You can make a house by cementing together bricks, stones, and wood, just like you can make a molecule by bonding together different types of atoms. You can also get your bricks, stones, and wood back by taking the house apart just like you can get your atoms back by taking the molecule apart. No matter how hard you try, though, you can't turn bricks into wood. Converting common metals like copper into gold or iron into gold would be like turning bricks into wood – it's simply not possible.

Matter Has Mass and Occupies Space

So far we've decided that the entire universe is composed of matter, which is in turn composed of atoms. Frequently, though, chemists want to know how much matter they actually have. To figure this out they rely on two fundamental properties of matter. All matter in the universe, from a teaspoon of salt to the Pacific Ocean, has mass and occupies space. When scientists measure how much space is taken up by a certain quantity of matter, they are measuring the object's volume. Obviously, the volume of the Pacific Ocean is a lot larger than the volume of a teaspoon of salt. Unfortunately, while volume is an important property, and plays an important role in a lot of different chemical experiments, volume is not the best way to determine how much matter you have.

Typically we think that the bigger something is, the more there is in it. That's certainly true a lot of the time in our everyday lives. If you pour yourself two cups of coffee in the morning, you'll be drinking twice as much coffee as you would have if you'd only poured yourself a single cup. Unfortunately, any time that we compare volumes in this way, we are making two assumptions that aren't always true in chemical experiments. First, we are assuming constant temperature. That's important, because the amount of space taken up by a certain quantity of matter depends on the temperature of that matter. In general, heating something up causes it to expand, and cooling something down causes it to contract. Secondly, when you compare volumes in everyday life, you are almost always comparing volumes of the same material. You can compare two cups of coffee to one cup of coffee, but how do you compare two cups of coffee to one cup of ice cream? It really doesn't make sense. Volume is not a good way to determine the quantity of matter that you have.

If you can't use volume to figure out how much matter you've got, what can you use? It turns out that the best way to determine quantities of matter is to use a measure known as mass. The mass of an object doesn't change with temperature, which makes it a lot easier to determine how much stuff you're dealing with, especially when you don't know what the temperature is or when the temperature keeps changing. Another good thing about mass is that an atom of a particular element always has the same mass (Strictly speaking that's not entirely true because of what are known as isotopes, but you won't need to worry about that now). For example, an atom of gold always has a mass of about 197 atomic mass units or daltons. Atomic mass units are units that we use to measure mass, just like a mile is a unit that we use to measure distance, and an hour is a unit that we use to measure time. Even when atoms are bonded together into molecules, the individual atoms have the same mass, meaning that by adding up all of the masses of the atoms in a molecule, it's fairly easy to figure out the mass of the molecule itself. You'll eventually learn how to do this.

The Difference Between Mass and Weight

Figure 1.21: The type of balance a chemist might use to measure the mass of an object.

One typical mistake that students make when learning about mass for the first time is confusing mass with weight. Again, this confusion is largely due to the fact that, in everyday English, we frequently use the word "weight" when we actually mean "mass". For example, when you say "I want to lose weight", what you really mean is, "I want to lose mass". In science, the word "weight" has a very specific definition that is different from what you might expect. Do not confuse the everyday meaning of the word "weight" with the scientific meaning of the word "weight" (Figure 1.21).

In science, mass is an intrinsic ("built-in") property of matter. The mass of an atom is the same regardless of the temperature or the other atoms that are bonded to it.

Similarly, the mass of an atom doesn't change depending on where it is. The mass of an atom is the same on Earth as it would be on the moon, or on Jupiter, or in the middle of space. Weight, on the other hand, does change with location. An object that weighs 240 pounds on earth would weigh about 40 pounds on the moon and that same object in a spaceship far away from any large mass would weigh zero (Figure 1.22). In all three cases, however, the object would have exactly the same mass.

Figure 1.22: With no large mass nearby, this spaceship is weightless.

In science, weight is a measurement of how strongly gravity pulls on an object. Weight depends on both the mass of the object and the force of gravity the object is experiencing. That's why your weight changes depending on where you're standing. In each case, your mass will be the same, but the force of gravity on Earth is different than the force of gravity on the moon, or on Jupiter and, as a result, your weight is different too. The force of gravity, however, doesn't change significantly on the surface of Earth. In other words, the force of gravity in California is approximately the same as the force of gravity in Australia. As a result, as long as you stick to the surface of the Earth, the more massive an object is, the more it weighs.

Lesson Summary

• All physical objects are made of matter.
• Matter itself is composed of tiny building blocks known as "atoms". There are only 118 different types of atoms known to man.
• Frequently, atoms are bonded together to form "molecules".
• All matter has mass and occupies space.
• Volume is a measure of how much space an object occupies. Volume is not a good measure of how much matter makes up any given object.
• Mass is an intrinsic property of matter that does not depend on temperature, location, or the way in which the matter is organized (how the atoms are bonded) As a result, mass is an excellent measure of how much matter is in any given object.
• "Mass" and "weight" have two very different scientific meanings.
• "Mass" only depends on how much matter is in an object. "Weight", on the other hand, depends on how strongly gravity pulls on an object.

Review Questions

1. What is matter?
2. What does weight mean?
3. In this chapter, we'll learn about atoms, which are the building blocks of all matter in the universe. As of 2011, scientists only know of 118 different types of atoms. How do you think it's possible to generate so many different forms of matter using only 118 types of building blocks?
4. Which do you think has more matter, a cup of water or a cup of mercury? Explain.
5. Decide whether each of the following statements is true or false.

   (a) Mass and weight are two words for the same concept.

   (b) Molecules are bonded together to form atoms.

   (c) Alchemists couldn't make gold out of common metals because gold is an element.

   (d) The symbol for Gold in the periodic table is Gd.

6. Would you have more mass on the moon or on Earth?
7. Would you have more weight on the moon or on Earth? The force of gravity is stronger on the Earth than it is on the moon.
8. Match the following terms with their meaning.

   (a) Mass	a. a measure of the total quantity of matter in an object
   (b) Volume	b. a measure of how strongly gravity pulls on an object
   (c) Weight	c. a measure of the space occupied by an object

9. For the following statements, circle all of the options that apply:
   • Mass depends on…

     (a) the total quantity of matter

     (b) the temperature

     (c) the location

     (d) the force of gravity

   • Volume depends on…

     (a) the total quantity of matter

     (b) the temperature

     (c) the object's shape (independent of size)

     (d) the object's size (independent of shape)

   • Weight depends on…

     (a) the total quantity of matter

     (b) the temperature

     (c) the location

     (d) the force of gravity

Vocabulary

atom

The basic building block of all matter. There are 118 known types of atoms. While atoms can be broken down into particles known as electrons, protons and neutrons, this is very difficult to do.

element

A type of atom. There are 118 known elements.

matter

Anything of substance that has mass and occupies space.

molecule

Two or more atoms bonded together. Specific molecules, like water, have distinct characteristics.

mass

An intrinsic property of matter that can be used to measure the quantity of matter present in a sample.

Periodic Table

A way of summarizing all the different atoms that scientists have discovered. Each square in the periodic table contains the symbol for one of the elements.

volume

A measurement of how much space a substance occupies.

weight

A measurement of how strongly gravity pulls on an object.

This material was adapted from the original CK-12 book that can be found here. This work is licensed under the Creative Commons Attribution-Share Alike 3.0 United States License