Molecules

Molecules

Middle School

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Learning Objectives

• Define a molecule and describe how atoms bond together to form one.

• Understand and explain the concept of the mass of a single molecule.

• Explain the main differences between what a molecule is and what a compound is.

• Understand that chemical bonds are what hold the atoms together inside a molecule.

Key Vocabulary

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Molecule

A particle made of two or more atoms that are chemically bonded together.

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Compound

A substance consisting of molecules that contain atoms from more than one element.

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Molecular Mass

The total mass of a molecule, which is the sum of the masses of its atoms.

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Bonds

The forces that hold two or more atoms together to form a molecule.

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What is a Molecule?

• A molecule is a tiny team of two or more atoms linked together.

• ​These atoms are held together by strong forces known as chemical bonds.

• Molecules can have atoms of the same element, like an oxygen molecule (O₂).

• They can also have different elements, like a water molecule (H₂O).

Multiple Choice

According to the slide, how are atoms held together to form a molecule?

• By gravity

• By static electricity

• By magnetic force

• By chemical bonds

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Compounds and Molecular Mass

What Is a Compound?

• A compound is a special kind of molecule that has atoms from different elements.

• For example, a water molecule, H₂O, is a compound made of two elements.

• It contains both hydrogen and oxygen atoms that have chemically bonded together.

What Is Molecular Mass?

• The molecular mass is the total mass of all the atoms inside a single molecule.

• It is calculated by adding up the atomic masses of every atom in the molecule.

• Each element has a unique atomic mass that is used in this important calculation.

Multiple Choice

What is the key difference between a general molecule and a compound?

• Molecules do not have mass.

• Compounds are held together by gravity, not bonds.

• A molecule must have at least three atoms.

• A compound must have atoms from more than one element.

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Common Misconceptions

Misconception	Correction
All molecules are compounds.	A molecule with one element type, like O2, is not a compound.
An atom and a molecule are the same.	An atom is a single unit; a molecule is a group of atoms.
Molecular mass and atomic mass are identical.	Atomic mass is one atom’s mass. Molecular mass is the total mass of atoms.

Multiple Choice

Why is a molecule of water (H₂O) considered a compound, while a molecule of oxygen (O₂) is not?

• Because water molecules are heavier than oxygen molecules.

• Because water has more atoms than oxygen.

• Because water is a liquid and oxygen is a gas.

• Because water contains atoms from two different elements (hydrogen and oxygen), while oxygen contains only one.

Multiple Choice

An atom of Carbon has an atomic mass of 12. An atom of Oxygen has an atomic mass of 16. What is the molecular mass of a carbon dioxide molecule (CO₂)?

• 44

• 40

• 32

• 28

Multiple Choice

If a newly discovered substance is made of molecules, what can you predict about its basic structure?

• It is made of a single type of atom.

• It must be a solid at room temperature.

• It cannot be broken down into simpler parts.

• It is composed of two or more atoms held together by chemical bonds.

Multiple Choice

Analyze the relationship between atoms, molecules, and compounds. Which statement accurately describes how they are related?

• Molecules are made of compounds, which are made of atoms.

• Atoms combine to form molecules, and molecules of different elements form compounds.

• Compounds exist independently of molecules and atoms.

• All compounds are atoms, but not all molecules are compounds.aAtoms are made of molecules, which in turn form compounds.

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Summary

• Two or more atoms are joined by chemical bonds to form a molecule.

• Molecules made from atoms of different elements are called compounds.

• The molecular mass is the total mass of all the atoms in a molecule.

• How atoms are bonded in a molecule determines the molecule's properties.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1

• 2

• 3

• 4