Chemical Reactions

Students use the phenomenon of how concrete is made to support their analysis of how chemical reactions produce new substances with different properties.

• Synthetic materials come from natural resources and impact society.
• To understand why a material has the properties it does, scientists begin with the atoms that make it up.
• Atoms are the smallest pieces of matter that have the properties of an element—substances that are made up entirely of one kind of atom.
• Atoms combine with other atoms in a variety of combinations to form all of the matter around us.
• Atoms combine with other atoms to form molecules (combinations of two or more atoms bonded together). The structure of a molecule is directly related to its properties.

• What natural resources are used to create concrete?
• Why does concrete have different properties from the natural resources it comes from?
• Why do scientists care about the atoms that make up materials?
• How can there be just 118 elements, and hundreds of thousands of different materials?
• How does a water molecule provide evidence that molecules have different properties from the atoms that make them up?
• What is the relationship between gravitational energy and chemical energy, which is energy stored in the bonds holding together atoms and molecules?

Misconception:  Mass is not conserved if a gas is produced during a chemical reaction.

Fact: Mass is always conserved. In an open system, we can’t measure the gas that’s produced, but that doesn’t mean it’s not there.

Atom : the smallest piece of matter that has the properties of an element; a combination of three subatomic particles: protons, neutrons, and electrons

Chemical change : a change that rearranges the chemical structure of a substance through a chemical reaction

Chemical energy : a form of potential energy that is stored in the bonds holding together atoms and molecules

Chemical reaction : a process that rearranges the atoms of the original substance into a new substance that has different properties from the original substance

Element : a substance made up entirely of one kind of atom

Endothermic : a process that absorbs energy from the environment

Exothermic : a process that releases energy into the environment

Matter : everything that has mass and takes up space

Molecule : a combination of two or more atoms bonded together

Physical change : a change that does not affect the chemical structure of a substance

Scale : the size, extent, or importance (magnitude) of something relative to something else

Thermal energy : the motion of atoms and molecules in a substance or object as its temperature increases

Mimicking the Stick-ability of Geckos

On a cold December day, an engineering student named Elliot Hawkes acted like a slow-motion Spiderman. He slowly climbed up a glass wall behind his science lab. He was able to stick to the glass because he was testing a new kind of material that was attached to his hands and feet.

The material used by Hawkes to scale the glass wall was designed by humans to mimic gecko feet. Geckos are lizards that can stick to almost any surface they walk on. They can run up smooth walls and across the ceiling without falling. This “stickability” is called adhesiveness. It is a property that gecko feet, glue, and tape all share.

How Geckos Stick

Geckos are able to stick to most surfaces because of their unique feet. Their feet are lined with millions of tiny hairs, called setae. The setae create an attraction between the gecko’s feet and the surface. Unlike adhesives such as glue or tape, however, the gecko’s sticky feet can attach and detach from the surface easily. This means the adhesiveness doesn’t have to be permanent, like glue.

Scientists are so intrigued by the gecko’s adhesive feet that they have been trying to mimic it, thinking about applications as common as wigs and toupees that remain in place, and as cutting edge as robots that can catch space junk (such as satellites that are no longer working).

Matter: Structure and Properties

Before a materials scientist like Elliot can design a new synthetic material or choose a natural resource for a specific function, they have to have a basic understanding of matter—anything that has mass and takes up space.

To understand why a material has the properties it does, scientists begin with the atoms that make it up. An atom is the smallest piece of matter that has the properties of an element—substances that are made up entirely of one kind of atom.

Aluminum foil is a synthetic material because it is created by humans. However, it is made from aluminum metal, which is a natural resource. Aluminum metal is made up of billions of aluminum atoms.

Atoms are so tiny that we cannot see them without special instruments. Because of this, scientists use scale to understand how atoms relate to everyday objects.

Scale is the size, extent, or importance (magnitude) of something relative to something else. For example, think about all of the atoms that make up a grapefruit. If each atom were the size of a blueberry, the grapefruit would be the size of Earth.

Parts of an Atom

Atoms themselves are made up of smaller particles. These particles include protons, neutrons, and electrons. These smaller particles are much smaller than the atom itself.

The protons and neutrons group together in the nucleus. If you were to open up the blueberry (representing the atom), the nucleus would be too small to see.

Scale of an Atom’s Parts

If you were to make the blueberry the size of a football field, you would just be able to see the nucleus. It would be the size of a small marble. The nucleus is very dense because it holds all of the atom’s protons and neutrons. Most of the atom’s mass—99.9 percent—comes from the protons and neutrons.

The electrons are in constant motion around the nucleus. However, most of the atom is filled with empty space. There are vast regions of space between each of the electrons and between the electrons and the nucleus.

Scientists use what they know about an atom’s structure to create a scale model of an atom. Scale models are useful for scientists who want to understand the atom as a system, and how the various parts of the atom interact.

Scientists often don’t work with individual atoms because they are too small to see without special instruments. Instead they work with elements, such as a gold bar or helium gas. An element is a pure substance. This means it is made entirely of one kind of atom that has distinct properties that do not vary from sample to sample.

It is the structure of the atoms that make up a substance that give that substance the properties it has. Many of an element’s properties are determined by the number of protons and neutrons its atoms have. Other properties are determined by an atom’s number and arrangement of electrons.

Most materials scientists agree that the single most important event that happened in their field came in 1864. This is when Russian scientist Dmitri Mendeleev put together a chart called the Periodic Table of Elements. This chart arranged all of the known elements according to their properties. When Mendeleev developed the periodic table, there were 63 known elements. His real genius was in predicting that elements existed that hadn’t yet been discovered.

His prediction was correct. There are currently 118 known elements, with the last four added just in 2016. These 118 elements are the only substances needed to make all of the materials that exist. In the human body, there are many billions of atoms, but scientists believe that more than 95 percent of the body is made up of just six elements: hydrogen, carbon, nitrogen, oxygen, phosphorus, and calcium.

The first 94 elements are believed to occur naturally. The rest are synthetic. Most of the elements that have been created last only seconds, at most, before breaking apart into smaller elements. Scientists are continuing to search for new elements.

For the hands-on activity in this lesson, students analyze the observable properties and thermal data produced by the combination of two substances to determine if the phenomena of a chemical reaction occurred. Students explore the phenomena of how the structure of matter changes during a chemical reaction, resulting in new and different properties of the product without creating or destroying mass in the process.