This NBC Learn video explains and illustrates the molecular structure of CO2; how the bonding of the carbon and oxygen molecules illustrates the Octet Rule, or Rule of 8; carbon dioxide and carbonation; the role of CO2 in the Earth's atmosphere; and how changing levels of CO2 can affect the temperature on the Earth's surface, including the oceans.
The Chemistry of CO2: Carbon Dioxide
BETH NISSEN: reporting:
It’s one of the few molecules regularly named in daily headlines, lead stories, and public conversation.
Unidentified Man: …emits some 2.1 billion tons of carbon dioxide a year.
Unidentified Man:…carbon dioxide emissions will be reduced.
Unidentified Man: …biggest producer of carbon dioxide.
Unidentified Man:…leading cause of global warming.
NISSEN: What’s behind the headlines on carbon dioxide? Here’s the inside story, really inside, down to the molecular level as you’ll see. To start, carbon dioxide, or CO2, is a gas: colorless, invisible at standard pressure and temperature. Under high pressure, CO2 can be compressed into a solid, known as dry ice, or dissolved in water, a process called carbonation. Its CO2 gas bubbles that put the pop in pop, or soda, depending on what part of the country you’re from. And, being a gas, can make you burp. You can also see CO2, or at least its effect, when you make bread. Yeast eats the starch in the flour, and expels carbon dioxide gas. CO2 gas expands when warmed, and makes the dough rise, the way helium gas expands a balloon. That’s not the way most people related carbon dioxide to warmth and warming. This is. The relationship of complex fluctuations in global temperatures, ice cover and sea levels, to this remarkably simple common molecule made of only three atoms, one atom of carbon, the C part of C02, attached or bonded to two atoms of oxygen, the O2 part of CO2, in a linear structure.
Great opportunity here to explain one of the fundamental rules in organic chemistry, the Octet Rule, or Rule of 8, a rule worth knowing because it applies to most of the elements in the Periodic Table, including the most common, carbon, nitrogen, and oxygen. Okay, hit refresh here. Atoms have a center, a nucleus, and a certain number of electrons that orbit the nucleus in shells. Molecules are formed when atoms combine. Atoms of most elements tend to combine so they each have eight electrons in their outer most shell. Carbon dioxide is a great example. A carbon atom has four electrons in its outer shell. It needs to connect with four more electrons to get the magic eight. An oxygen atom has six electrons in its outer shell. It needs to connect to two more to get to eight. What happens is a little like the card game “go fish,” atomic version. The atoms align in specific ways to trade, or share electrons so they can get the electron sets of eight they need. Two oxygen atoms connect to opposite sides of one carbon atom, which gives each the two electrons it needs to make eight. See? The carbon atom in the middle gets two electrons from the oxygen atom on one side, and two from the one on the other, for a total of eight on its outer, or valence shell. Sharing pairs of electrons is called covalent bonding.
Now, back to the bigger picture, CO2 in our air and atmosphere, and in fact, throughout deep space in ice form, part of the makeup of planets. NASA rovers found CO2 icecaps on Mars. Earth’s surface is much warmer than space, so most of the C02 on Earth is present as an atmospheric gas. Carbon dioxide makes up less than half of one percent of the air we breathe. Air is mostly nitrogen and oxygen. Eruptions of volcanoes, like the one in Iceland called…like the one in Iceland, add CO2 to the atmosphere, and of course, so does the carbon or life-cycle. Plants take in CO2, along with sunlight and water, and give out oxygen, animals and humans take in oxygen, and give out C02. And then, there’s this, the burning of fossil fuels in power plants, automobiles, and factories. Oil, gasoline, coal, carbon-based fuels. In fact, the word carbon comes from the Latin word for coal. As more of these fuels and organic matter like wood and crop stalks are burned by the planet’s growing population and industry, all this additional carbon does exactly what you’ve just seen: it bonds with oxygen in the air. Air is 20% oxygen, and makes, yes, more carbon dioxide. Where does it all go? An estimated 57% of this cook-fire, tail pipe, smoke stack carbon dioxide, is cycled into the oceans, covering 70% of the Earth’s surface. Plants eat up some, most of the rest goes into the air. In the oceans and the air, more CO2 is causing serious problems. In the oceans, well, click rewind to making carbonated drinks, remember, by dissolving CO2 into H20. That, logically enough, makes H2C03, also known as carbonic acid, a weak acid, although strong enough to remove rust from chrome. Okay, fast-forward again, more CO2 in sea water, more carbonic acid, more acidification of the oceans. And in the air, buildup of C02 and other so called greenhouse gases in the atmosphere, acts like a marathoner’s thin post-race blanket, holding essential body heat close to earth’s skin, keeping the average surface temperature at about 59 degrees. Without this trap, the warmth from the sun would escape back into space, and average temperature on earth would be just below one degree Fahrenheit. But adding too many layers of C02 can have the opposite effect, trap too much heat, enough to melt ice caps, raise ocean levels, raise ocean and air temperatures, contribute to global warming. There’s much more to know about C02 and carbon credits, carbon footprints, and carbon capture. Maybe think of this video as carbon capture of another kind.
Carbon is the backbone of life on Earth. We are made of carbon, we eat carbon, and our civilizations — our economies, our homes, our means of transport — are built on carbon. We need carbon, but that need is also entwined with one of the most serious problems facing us today: global climate change.
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