Molecules

Once students understand the basic structure of atoms, they then focus on how atoms are like children’s building blocks, forming molecules and compounds by combining with other atoms to create all of the matter in the universe. 

• Atoms combine with other atoms to form molecules (combinations of two or more atoms bonded together) and compounds (combinations of two or more different kinds of atoms bonded together). 
• The structure of a molecule or compound is directly related to its properties. In a chemical reaction, the bonds that hold together molecules and compounds are broken and rearranged to form new molecules and compounds, which is why chemical reactions create new substances with different properties. However, the total number and kind of atoms is conserved because matter is never created or destroyed.
• Molecules and compounds bond because of the attraction of protons and electrons. When two atoms approach one another, the electrons of each are attracted to the protons of the other.
  
  

• What causes atoms to bond?
• Why are some bonds represented by a single line, while others have a double or triple line?
• Why is water both a molecule and a compound?
• What is the difference between a liquid and a gas?
• How is energy related to chemical reactions?
• How would you explain the cause-and-effect relationship between the rearrangement of atoms and molecules in a chemical reaction and the different properties that the products have from the reactants?
  
  

Misconception: Atoms are created and/or destroyed in a chemical reaction, which is what produces the new substances.

Fact: The number and kind of atoms remain the same before and after a chemical reaction, but they have been rearranged.

Misconception: After a chemical reaction, the product is a mixture made up of the old substances, which still exist, and therefore is not a new substance.

Fact: Chemical reactions produce new substances because they break down the molecules that make up the reactants (not the atoms themselves) and rearrange the atoms to form new substances.

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

Chemical Energy : a form of potential energy held in the bonds of atoms and molecules

Chemical Reaction :  a change that rearranges the atoms of the original substances into a new substance that has different properties from the original substances

Compound : a combination of two or more different kinds of atoms bonded together

Molecule : a combination of two or more atoms bonded together

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

Libyan Desert Glass

In 1996, an Italian scientist noticed an unusual gem in one of Tutankhamen’s necklaces. Tutankhamen was an Egyptian pharaoh who ruled between 1331-1323 BC. He is sometimes called King Tut. The Italian scientist was interested in a yellow- green gem that he saw in King Tut’s necklace. When the gem was tested, it was found to be glass. However, it was older than the oldest Egyptian civilization.

What Formed the Glass?

How this glass was made is a question that scientists are still trying to answer. It came from a stretch of desert in Africa called the Libyan Desert. More than one thousand tons of this kind of glass have been found there. Scientists have dated this glass to be more than 26 million years old. It is generally yellow, and it can be translucent or almost opaque. Translucent substances can partly be seen through. Opaque substances block all light.

Scientists believe that this Libyan Desert glass may have formed when a meteorite hit Earth or when a comet from space exploded in Earth’s atmosphere. Both of these events would have provided the extreme temperatures necessary to change the desert sand into glass.

Glass’s State of Matter

Glass is unlike any material on Earth. Scientists sometimes refer to glass as a rigid liquid because it isn’t quite a solid, and it’s not exactly a liquid. This is because of the extreme temperatures that form glass.

Whether a substance is a solid, liquid, or gas depends on the amount of thermal energy present. All matter has thermal energy, which is the motion of atoms and molecules in a substance or object as its temperature increases. Temperature is a measure of heat. Heat is energy transferred when two objects or systems are at different temperatures. It always transfers from hotter substances to cooler substances. The faster that atoms and molecules move, the more thermal energy they have and the warmer they become.

Sand is a solid at room temperature. The atoms in a solid are closely packed together. They are always moving, but because of how close they are, they can only vibrate in place. They cannot move past one another. Because of this, solids keep their shape until something changes them.

When thermal energy is added to solids, the atoms or molecules begin to move more quickly. When enough energy is added, they will expand and become a liquid. The temperature at which a substance changes from a solid to a liquid is a property of matter called its melting point.

This is what happens when lightning or a meteor comes into contact with sand. When sand is heated to such a high temperature that it melts, it becomes a liquid. Its atoms and molecules are moving much faster, and can slide past one another. Different substances have different melting points depending on how much energy is needed to change them from a solid to a liquid. This in turn depends on the kind of atoms that make them up.

In this lesson, students explore the phenomena of molecular bonding by modeling the atomic composition of simple molecules with varying levels of complexity. Students use their model molecules to analyze how the properties of substances depend partly on the elements that make them up, but also on the ways in which the elements bond and the quantities of each element present.