Rocket taps the iron pan hanging over the stove. "Element," he says. He taps the copper bottom of a pot. "Element."
He points at Raven's ring. "Gold. Element." Then he takes a deep breath. "And I just breathed in two more."
Raven laughs. "What do you notice about the ones you can see? They are all metals."
"The air ones are invisible," Rocket says. "Nitrogen and oxygen. Most of the air is nitrogen, right?"
Nova hovers near the window, her light pulsing gently. "Most of the air, yes. But not all of it," she says. "Think about what you breathe out."
"Carbon dioxide," Rocket says. "Carbon joined to oxygen. That is not an element. That is two of them stuck together."
Raven writes a new heading in the Bench Log: Elements I Met Today.
Air is a mixture of gases: 78 percent nitrogen and 21 percent oxygen. The rest is traces of water vapor, carbon dioxide, argon and other gases.
Oxygen and nitrogen occur in nature as molecules of two atoms each. A molecule is a group of two or more atoms bonded together.
Water is a molecule too. Each water molecule contains two atoms of hydrogen and one atom of oxygen, which is why chemists write it H2O.
There are millions of different possible molecules, but they are all built from the 118 elements.
Some elements have been known for centuries: gold, silver, iron and copper. Others were created in a laboratory only recently.
Iron is a rigid solid metal. A simple skillet can be made from cast iron.
Copper is a good conductor of electricity and is very flexible. It is widely used to carry electric current in wires and appliances.
Gold is soft and easily shaped, so many civilizations have used it for jewelry.
Aluminum is less dense than iron, so airplanes, rockets and some automobile parts are made from aluminum.
Most elements do not exist on their own in nature. They are so reactive that they are found only combined with other elements.
| Element | Symbol | Where you meet it |
|---|---|---|
| Nitrogen | N | About 78 percent of the air |
| Oxygen | O | About 21 percent of the air; also in every water molecule |
| Hydrogen | H | Two atoms in every water molecule |
| Iron | Fe | A cast iron skillet |
| Copper | Cu | Wires that carry electric current |
| Gold | Au | Jewelry |
| Aluminum | Al | Airplane and rocket parts |
This week you learned that matter is anything with mass and volume, and that air counts. You measured mass with a scale and volume with water.
You met atoms, the building blocks of matter, and the 118 elements on the periodic table.
Next week you will look at how those particles behave in solids, liquids and gases.
| Week review | True or false? |
|---|---|
| Air is a mixture of gases, mostly nitrogen. | ? |
| A molecule is a group of two or more atoms bonded together. | ? |
| Water is an element. | ? |
| Most elements are found alone in nature, not combined. | ? |
| Gold, silver, iron and copper have been known for centuries. | ? |
Strong week, chemist. Tomorrow is Bench Day: a family matter hunt around the whole home.