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<ul id="x-ck12-OTI2NjQ4ZTg1N2Q1YTAwMjhlYjhkYjQ1ZDIwZjY4ZTE.-luq">
<li>Identify the type of matter called a <a class="x-ck12-crossref" title="Compound" href="/c/physical-science/compound">compound</a>.</li>
<li>Explain how the same elements can form different compounds.</li>
<li>List two types of chemical compounds.</li>
</ul>
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<p id="x-ck12-OThlZDYwZGIxYzVmMTMzNTlmYjYxMDYwYTljOThlNDk.-ipy"><span class="x-ck12-img-inline"><!-- @@author="" --><!-- @@license="" --><img data-flx-url="/flx/show/image/201412291419892635366427_9bfc95c2edefec85aca1c80424d2f5b5-201412291419895141455444.jpg" src="https://dr282zn36sxxg.cloudfront.net/datastreams/f-d%3Aadbe3fa9de3276faef1a39607a0b690e37edc85d5a826eb9ee12935f%2BIMAGE_TINY%2BIMAGE_TINY.1" width="400" alt="" /></span></p>
<p id="x-ck12-YWU4N2I4YjYyMDZkYTQ5MDkyNTZhMGQwODNlYjAzZmQ.-kad">Look at all the colors you can make by mixing together just a few colors of paint. In the photo above, the rainbow of colors on the brush formed from just four paint colors: green, yellow, red, and blue. The same thing is true of matter in general. By combining just a few different elements, you can form many different chemical compounds.</p>
<h3 id="x-ck12-V2hhdCBBcmUgQ29tcG91bmRzPw..">What Are Compounds?</h3>
<p id="x-ck12-N2U3Nzg5NmI0NjNhYzMzMzJiNWViYjBiYzM0N2I0OTk.-bfg">A <strong>compound</strong> is a unique substance that forms when two or more elements combine chemically. Compounds form as a result of chemical reactions. The elements in compounds are held together by chemical bonds. A <a class="x-ck12-crossref" title="Chemical Bond" href="/c/physical-science/chemical-bond">chemical bond</a> is a force of attraction between atoms or ions that share or transfer <a class="x-ck12-crossref" title="Valence Electrons" href="/c/physical-science/valence-electrons">valence electrons</a>.&#160;</p>
<div id="x-ck12-x71" itemprop="video" itemscope="" itemtype="http://schema.org/VideoObject"><iframe id="x-ck12-x-ck12-LUhqTW9UdGhFWjA." src="/flx/show/video/http%3A//www.youtube.com/embed/-HjMoTthEZ0" name="195" frameborder="0" height="380" width="500"></iframe></div>
<p id="x-ck12-NDk2MTViNzdhNDdhZjgxOGRjYjY5MWY5YThjZjdhYjM.-zjh">Water is an example of a common chemical <a class="x-ck12-crossref" title="Compound" href="/c/physical-science/compound">compound</a>. As you can see in the <strong>Figure</strong> <a href="#x-ck12-TVNfUFNfM18xXzJfbW9sZWN1bGVz">below</a>, each <a class="x-ck12-crossref" title="Water" href="/c/biology/water">water</a> molecule consists of two atoms of hydrogen and one <a class="x-ck12-crossref" title="Atom" href="/c/physical-science/atom">atom</a> of oxygen. Water always has this 2:1 ratio of hydrogen to oxygen. Like water, all compounds consist of a fixed ratio of elements. It doesn’t matter how much or how little of a <a class="x-ck12-crossref" title="Compound" href="/c/physical-science/compound">compound</a> there is. It always has the same <a class="x-ck12-crossref" title="Composition" href="/c/earth-science/composition">composition</a>.</p>
<div id="x-ck12-NTc0NDYwZTVlYzc2ZWE4YWMyODg4MDQ1ODQxMmZlODQ.-07e" class="x-ck12-img-postcard x-ck12-nofloat"><!-- @@author="Jodi So" --><!-- @@url="CK-12 Foundation" --><!-- @@license="CC BY-NC 3.0" -->
<p id="x-ck12-v7h"><img data-flx-url="/flx/show/THUMB_POSTCARD/image/201412291419892635388588_346d3430d2c73ff668a727c8971858bc-201412291419895141607543.png" src="https://dr282zn36sxxg.cloudfront.net/datastreams/f-d%3A7baaec13ae032d19ac9039e49892393cec2ac905c102ab5f46a7328a%2BIMAGE_THUMB_POSTCARD_TINY%2BIMAGE_THUMB_POSTCARD_TINY.1" id="x-ck12-TVNfUFNfM18xXzJfbW9sZWN1bGVz" title="W" alt="W" longdesc="All%20water%20molecules%20have%20two%20hydrogen%20atoms%20%28gray%29%20and%20one%20oxygen%20atom%20%28blue%29.%20" /></p>
<p id="x-ck12-NjA1MGIyYjA0OWNlOTdhMWVlYzA4MmY1ZDQxZDU3NGM.-mrg">All water molecules have two hydrogen atoms (gray) and one oxygen atom (blue).</p>
</div>
<p id="x-ck12-NzIxYzZlNWFhZmVjMzUzZmNmZDExMjg4OWJlYzYyNzg.-7zx"><strong>Q:</strong> Sometimes the same elements combine in different ratios. How can this happen if a compound always consists of the same elements in the same ratio?</p>
<p id="x-ck12-NDgyMGViYTBmNjdlNjI2M2UxNTAzNWU0YmQ1OTJlNjk.-hzw"><strong>A:</strong> If the same elements combine in different ratios, they form different compounds.</p>
<h3 id="x-ck12-U2FtZSBFbGVtZW50cywgRGlmZmVyZW50IENvbXBvdW5kcw..">Same Elements, Different Compounds</h3>
<p id="x-ck12-NWM4NTJmODJiODUyOTY4OWViZjI0MzAwMzE3YmM2YjU.-x1e">Look at the <strong>Figure</strong> <a href="#x-ck12-TVNfUFMtMzEyX0xpcXVpZHM.">below</a> of <a class="x-ck12-crossref" title="Water" href="/c/biology/water">water</a> (H<sub>2</sub>O) and hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), and read about these two compounds. Both compounds consist of hydrogen and oxygen, but they have different ratios of the two elements. As a result, <a class="x-ck12-crossref" title="Water" href="/c/biology/water">water</a> and hydrogen peroxide are different compounds with different properties. If you’ve ever used hydrogen peroxide to disinfect a cut, then you know that it is very different from water!</p>
<div id="x-ck12-OWQyMzRlMDk0Nzg5MzY5ZGYyMzE5NzNkZGQxNTAwYmU.-64o" class="x-ck12-img-postcard x-ck12-nofloat"><!-- @@author="Left: Derek Jensen; Right: Robert Taylor (Flickr:Bobolink)" --><!-- @@url="Left: http://commons.wikimedia.org/wiki/File:Glass-of-water.jpg; Right: http://www.flickr.com/photos/bobolink/3456322557/" --><!-- @@license="Left: Public Domain; Right: CC BY 2.0" -->
<p id="x-ck12-o8f"><img data-flx-url="/flx/show/THUMB_POSTCARD/image/201412291419892635418452_8a2ef0c950cfbf850e779b697691ac00-201412291419895141764038.jpg" src="https://dr282zn36sxxg.cloudfront.net/datastreams/f-d%3Af7adb7c9ca94dcd5ee0d1f93084b2ad1b258178f7c8a2526cc2b7c0e%2BIMAGE_THUMB_POSTCARD_TINY%2BIMAGE_THUMB_POSTCARD_TINY.1" id="x-ck12-TVNfUFMtMzEyX0xpcXVpZHM." title="Water and hydrogen peroxide have very different properties" alt="Water and hydrogen peroxide have very different properties" longdesc="Water%3A%20Water%20is%20odorless%20and%20colorless.%20%20We%20drink%20it%2C%20bathe%20in%20it%2C%20and%20use%20it%20to%20wash%20our%20clothes.%20%20In%20fact%2C%20we%20can%27t%20live%20without%20it.%20%20%20Hydrogen%20Peroxide%3A%20Hydrogen%20peroxide%20is%20also%20odorless%20and%20colorless.%20%20It%27s%20used%20as%20an%20antiseptic%20to%20kill%20germs%20on%20cuts.%20%20It%27s%20also%20used%20as%20bleach%20to%20remove%20color%20form%20hair.%20" /></p>
<p id="x-ck12-ZWJkZjQxMzAzZjIxZjQwZDg3MDZjYzhkZjI4YTYyZTU.-wed">Water: Water is odorless and colorless. We drink it, bathe in it, and use it to wash our clothes. In fact, we can't live without it. Hydrogen Peroxide: Hydrogen peroxide is also odorless and colorless. It's used as an antiseptic to kill germs on cuts. It's also used as bleach to remove color form hair.</p>
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<p id="x-ck12-Yjg4YzEwNTE4OTM1MGZhMWUxYmY1MDZlNzUzMWI3MzA.-f5r"><strong>Q:</strong> Read the <strong>Figure</strong> <a href="#x-ck12-TVNfUFMtMzEyX0dhc2Vz">below</a> about carbon dioxide (CO<sub>2</sub>) and carbon monoxide (CO). Both compounds consist of carbon and oxygen, but in different ratios. How can you tell that carbon dioxide and carbon monoxide are different compounds?</p>
<p id="x-ck12-MGM2MTc0ZmI2MmUzNmJmZWEyMTUxZmIyNzFjODBiMGU.-6hp"><strong>A:</strong> You can tell that they are different compounds from their very different properties. Carbon dioxide is a harmless <a class="x-ck12-crossref" title="Gas" href="/c/physical-science/gas">gas</a> that living things add to the atmosphere during respiration. Carbon monoxide is a deadly gas that can quickly kill people if it becomes too concentrated in the air.</p>
<div id="x-ck12-ZmZiOTdhNDczMDRhM2EzODE1YjY4YjNlOGVhMzc2MTY.-eog" class="x-ck12-img-postcard x-ck12-nofloat"><!-- @@author="Left: Image copyright arek_malang, 2013; Right: User:Sideroxylon/Wikimedia Commons" --><!-- @@url="Left: http://www.shutterstock.com; Right: http://commons.wikimedia.org/wiki/File:CO_detector.JPG" --><!-- @@license="Left: Used under license from Shutterstock.com; Right: Public Domain" -->
<p id="x-ck12-uu3"><img data-flx-url="/flx/show/THUMB_POSTCARD/image/201412291419892635434099_5402a9cfb63c2b1d35778fbfd1ab64a5-201412291419895142004107.jpg" src="https://dr282zn36sxxg.cloudfront.net/datastreams/f-d%3A376a807ce600c718e5b3634235ecf81be9f3561903459e5c636c7eb6%2BIMAGE_THUMB_POSTCARD_TINY%2BIMAGE_THUMB_POSTCARD_TINY.1" id="x-ck12-TVNfUFMtMzEyX0dhc2Vz" title="Carbon dioxide and carbon monoxide have very different properties" alt="Carbon dioxide and carbon monoxide have very different properties" longdesc="Carbon%20Dioxide%3A%20Every%20time%20you%20exhale%2C%20you%20release%20carbon%20dioxide%20into%20the%20air.%20%20It%27s%20an%20odorless%2C%20colorless%20gas.%20%20Carbon%20dioxide%20contributes%20to%20global%20climate%20change%2C%20but%20it%20isn%27t%20directly%20harmful%20to%20human%20health.%20Carbon%20Monoxide%3A%20Carbon%20monoxide%20is%20produced%20when%20matter%20burns.%20%20It%27s%20a%20colorless%2C%20odorless%20gas%20that%20is%20very%20harmful%20to%20human%20health.%20%20In%20fact%2C%20it%20can%20kill%20people%20in%20minutes.%20%20Because%20you%20can%27t%20see%20or%20smell%20carbon%20monoxide%2C%20it%20must%20be%20detected%20with%20an%20alarm.%20" /></p>
<p id="x-ck12-ZjY3YzhlMTJhOTZkMGNjYTNmZGM4MWI4OThkZDNiYjc.-bdn">Carbon Dioxide: Every time you exhale, you release carbon dioxide into the air. It's an odorless, colorless gas. Carbon dioxide contributes to global climate change, but it isn't directly harmful to human health. Carbon Monoxide: Carbon monoxide is produced when matter burns. It's a colorless, odorless gas that is very harmful to human health. In fact, it can kill people in minutes. Because you can't see or smell carbon monoxide, it must be detected with an alarm.</p>
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<h3 id="x-ck12-VHlwZXMgb2YgQ29tcG91bmRz">Types of Compounds</h3>
<p id="x-ck12-Y2VjMmMxNjIxYjcyYzQzMTQ5ZTRhNjk4MjUwNjM3MzE.-bxp">There are two basic types of compounds that differ in the nature of the bonds that hold their atoms or ions together. They are covalent and ionic compounds. Both types are described below.&#160;</p>
<div id="x-ck12-1y6" itemprop="video" itemscope="" itemtype="http://schema.org/VideoObject"><iframe id="x-ck12-x-ck12-YlE2XzhpTWQ4WU0." src="/flx/show/video/http%3A//www.youtube.com/embed/bQ6_8iMd8YM%3Fwmode%3Dtransparent%26rel%3D0%26hash%3D441c0e53a307d506e4ffeff4637d0e6a" name="79972" frameborder="0" height="380" width="500"></iframe></div>
<ul id="x-ck12-MWFkMDE4NzA1OTRmYmMzOGE1N2JiNTE0ODE3ODdlYjI.-z7p">
<li>Covalent compounds consist of atoms that are held together by covalent bonds. These bonds form between nonmetals that share <a class="x-ck12-crossref" title="Valence Electrons" href="/c/physical-science/valence-electrons">valence electrons</a>. Covalent compounds exist as individual molecules. Water is an example of a covalent compound.</li>
<li>Ionic compounds consist of ions that are held together by ionic bonds. These bonds form when <a class="x-ck12-crossref" title="Metals" href="/c/physical-science/metals">metals</a> transfer electrons to nonmetals. Ionic compounds exist as a matrix of many ions, called a crystal. Sodium chloride (table salt) is an example of an ionic compound.</li>
</ul>
<h3 id="x-ck12-U3VtbWFyeQ..">Summary</h3>
<ul id="x-ck12-NmY0NjY3ZTdhOTJhNzc5ZWIxOTU5MTE4ZjY0YWZjMzg.-smq">
<li>A compound is a unique substance that forms when two or more elements combine chemically.</li>
<li>A compound always consists of the same elements in the same ratio. If the same elements combine in different ratios, they form different compounds.</li>
<li>Types of compounds include covalent and ionic compounds. They differ in the nature of the bonds that hold their atoms or ions together.</li>
</ul>
<h3 id="x-ck12-UmV2aWV3">Review</h3>
<ol id="x-ck12-NTdlZjU4NjUyMzA5NzQ4M2JjMDljNDRhMjI2NDRlOWM.-mkx">
<li>What is a compound?</li>
<li>A <a class="x-ck12-crossref" title="Mixture" href="/c/physical-science/mixture">mixture</a> is a combination of two or more substances in any proportions. An example of a mixture is lemonade, which contains water, lemon juice, and sugar. How do compounds differ from mixtures such as lemonade?</li>
<li>Compare and contrast ionic and covalent.</li>
</ol>
<h3 id="x-ck12-RXhwbG9yZSBNb3Jl">Explore More</h3>
<p id="x-ck12-MDM5Mjg5OGYyYTYwZDM3NmFhYmNhOTU1YWNjMGU4MzQ.-gjw">Watch the video about compounds, and then answer the questions below.&#160;</p>
<div id="x-ck12-zp3" itemprop="video" itemscope="" itemtype="http://schema.org/VideoObject"><iframe id="x-ck12-x-ck12-TFJWVzB0Z1NMUkk." src="/flx/show/video/http%3A//www.youtube.com/embed/LRVW0tgSLRI%3Fwmode%3Dtransparent%26rel%3D0%26hash%3D1c0d4dcc3858fd26e4a07a970a9f8e68" name="82366" frameborder="0" height="380" width="500"></iframe></div>
<ol id="x-ck12-NjRhZDQ4MGQ5NDMxM2RhZTNhNjA5NzU4NGUyZjk2Y2Y.-wau">
<li>What force holds together atoms in compounds?</li>
<li>Name a <a class="x-ck12-crossref" title="Gas" href="/c/physical-science/gas">gas</a> that consists of two atoms of the same <a class="x-ck12-crossref" title="Element" href="/c/physical-science/element">element</a> bonded together. Do the molecules of this gas represent a compound? Why or why not?</li>
<li>Identify at least one property of water that differs from the properties of the elements that form it.</li>
<li>Which two elements make up the compound named butane? What is the ratio of these two elements in butane? How would you use chemical symbols to represent butane?</li>
</ol>
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