Free preview Classifying matter

Elements and atoms

Learn about elements as the building blocks of matter. Understand how atoms represent the smallest particle of an element. Use the periodic table as your guide to the elements.

▶ Elements

Elements are the fundamental building blocks of all matter, just as letters form the basis of all writing. With only about 100 natural elements, nature constructs everything around us—from tiny microbes to vast oceans and stars. These elements, represented by symbols on the periodic table, combine in countless ways to create the diverse materials that make up the universe.

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▶ Atoms

An atom is the smallest particle of an element that still retains all the properties of that element. Early philosophers imagined atoms as indivisible units that make up all matter, an idea revived and developed by scientists like John Dalton. Atoms are incredibly small and numerous—a single gold ring contains more atoms than stars in the universe, highlighting their fundamental role in forming the matter we see.

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▶ The periodic table

The periodic table organizes all known elements by atomic number, displaying them in rows and columns called periods and groups. Each element’s square includes its symbol, atomic number, and atomic mass. Groups of elements often share similar properties, like the reactive metals in Group 1, and the inert noble gases in Group 18. The table also separates metals, nonmetals, and metalloids, helping us see patterns in elemental behavior and relationships.

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📄 Learn and try: Elements, atoms, and the periodic table

##Elements are building blocks of matter

You’re reading this on an electronic device. Have you ever thought about the materials used to build this device? What are they? And what do we know about these substances?

The building blocks of [[☃ definition 1]] are called elements. There are about $100$ naturally occurring elements that make up everything around you, including the device you’re using right now.

For example, the element lithium is used to make batteries that power our computers and smartphones. If the device you’re using has a touchscreen, the screen contains a layer of indium and tin oxides.

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##Elements are pure substances

A pure substance is a type of matter that contains only one type of particle throughout. Elements are examples of pure substances because they contain only one type of atom.

For example, copper is an element that can be molded into copper tubing. If you could zoom in on the copper tubing in the image below, you’d see it’s made from only copper atoms. No other elements—just copper!

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##Elements are made of atoms

How many times could you tear a single piece of paper in half? It’s easy to imagine tearing it in half one or two times. But as the halves get smaller, this becomes a more difficult task. A similar thought process led to the first ideas about the smallest pieces of matter. Is there a point where we have a single particle that simply cannot be split anymore?

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The Greeks developed a word for this idea—atomos, which means “uncuttable.” Today, we use the word atom to describe the smallest particle of an element that still retains the properties of that element.

Atoms are incredibly small. So small that several trillion atoms of carbon would fit in the dot above the letter ‘i’ in this sentence. That’s more than $1{,}000{,}000{,}000{,}000$ atoms!

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The periodic table organizes all 118 elements

There are $118$ known elements. Imagine if you had $118$ different keys, each one opening up a different door. You would need a system to stay organized! The periodic table is how scientists around the world keep the elements organized.

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In each square on the periodic table, there is a small number at the top. Every element has its own unique number, similar to an “ID number.” This value is known as the atomic number and is what we use to arrange the elements on the periodic table.

There is another number in each square, written along the bottom. This is the atomic mass. This value is often not a whole number because it represents the average mass of all versions of an element.

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You’ll also notice the letters in each square. These are the symbols of the elements. Each element has a unique symbol, with either one or two letters. For example, copper is $\ce{Cu}.$ Notice that only the first letter is capitalized.

These symbols are universal. Whether you are looking at a periodic table in the United States, India, China, or Peru, copper is always $\ce{Cu}.$

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##Elements with similar characteristics are grouped together on the periodic table

The periodic table is divided into seven rows and eighteen columns. The horizontal rows are known as periods. For example, copper is in the same period as potassium, nickel, and bromine.

The vertical columns of the periodic table are known as groups. Elements in the same group often have similar characteristics. For example, all elements in the last group (group $18$) are non-reactive gases. This group is known as the noble gases.

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##The periodic table separates metals and nonmetals

An element’s location on the periodic table tells us a lot about its properties. In addition to showing which group an element is in, the periodic table also separates metals from nonmetals. Notice the “stairstep” line on the right side of the periodic table shown below. This line establishes the boundary between these two groups of elements.

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Metals are found on the left side of the stairstep line, and are colored blue-gray on the periodic table above. Metals are shiny, conductive substances with high melting points. As you can see, most elements are metals.

Nonmetals are found on the right side of the stairstep line, and are colored lavender on the periodic table above. Nonmetals are dull, brittle, non-conductive substances with low melting points. There are fewer nonmetals than metals, but they are all very important. Notice that hydrogen is the only nonmetal located on the left side of the periodic table.

A few elements have properties of both metals and nonmetals. These six elements are known as metalloids, and are colored tan on the periodic table above. As you might expect, metalloids are located at the border between metals and nonmetals.

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##Check for Understanding

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##Key points

Elements are the building blocks of matter. There are around $100$ naturally occurring elements.
An atom is the smallest part of an element that shares the same properties as the element.
The periodic table organizes the elements based on increasing atomic number and is arranged in periods and groups.
On the periodic table, each element has a unique symbol. These symbols are universally used.
An element’s location on the periodic table indicates various properties, such as whether the element is a metal, nonmetal, or metalloid.

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