Structure of Matter

Structure of Matter

Middle School

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Learning Objectives

• Describe the basic structure of an atom and its main particles.

• Compare protons, neutrons, and electrons by their charge and location.

• Use atomic number to identify an element and atomic mass for its mass.

• Distinguish between elements, compounds, and molecules as different pure substances.

• Compare the arrangement of atoms in crystalline and amorphous solids.

Key Vocabulary

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Matter

Matter is anything that has mass and takes up space, which is also known as volume.

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Atom

An atom is the smallest basic unit of a chemical element, retaining its unique chemical properties.

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Proton

A proton is a subatomic particle with a positive charge, located in the nucleus of an atom.

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Neutron

A neutron is a subatomic particle with no electrical charge, found within the atomic nucleus.

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Electron

An electron is a negatively charged particle that travels in the cloud surrounding an atom's nucleus.

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Atomic Number

The atomic number is the total count of protons in an atom's nucleus, uniquely identifying an element.

Key Vocabulary

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Atomic Mass

The average combined mass of all the protons and neutrons within an atom's nucleus.

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Element

A pure substance consisting of only one type of atom, identified by its atomic number.

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Compound

A substance that is formed when two or more different elements are chemically bonded together.

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Molecule

Two or more atoms, which can be the same or different, that are bonded together.

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Crystalline Solid

A type of solid material whose atoms are arranged in a highly ordered, repeating pattern.

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What is Matter and What are Atoms?

What is Matter?

• ​All the various substances we see in the world are a form of matter.

• ​​It is defined as anything that takes up space, also known as having volume.

• ​Matter is also defined by having mass, which is the amount of material in an object.

What are Atoms?

• ​All matter is composed of extremely tiny particles that serve as its building blocks.

• ​​These fundamental building blocks of all matter are known by the name of atoms.

• ​An atom is the smallest particle of an element that has the properties of that element.

Multiple Choice

According to its scientific definition, what must be true for something to be classified as matter?

• It must be visible to the naked eye.

• It must have a specific color and shape.

• It must be a solid substance.

• It must have both mass and volume.

Multiple Choice

What is the relationship between matter and atoms?

• Atoms are the fundamental building blocks that make up all matter.

• Matter is a type of particle found inside an atom.

• Only certain types of matter are composed of atoms.

• Atoms and matter are two completely unrelated concepts.

Multiple Choice

If you could break down a pure element into its smallest possible component that still retains the properties of that element, what would you have?

• A molecule of that element.

• A substance of that element.

• A particle of that element.

• An atom of that element.

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Inside the Atom: Subatomic Particles

• Protons have a positive (+) charge and are located in the atom's nucleus.

• Neutrons have no electrical charge (are neutral) and are also in the nucleus.

• Electrons have a negative (-) charge and rapidly move in the electron cloud.

• The nucleus has most of the mass; the electron cloud has most of the volume.

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Multiple Choice

Which of the following are the three subatomic particles that make up an atom?

• Protons, neutrons, and electrons

• The nucleus, the electron cloud, and the charge

• Positive, negative, and neutral

• Mass, volume, and charge

Multiple Choice

What is the relationship between the charge of the nucleus and the charge of the electron cloud?

• The nucleus is positively charged, while the electron cloud is negatively charged.

• The nucleus has no mass, while the electron cloud contains all the mass.

• The nucleus is large and contains electrons, while the electron cloud is small.

• The nucleus has a neutral charge, while the electron cloud has a positive charge.

Multiple Choice

What conclusion can be drawn about the structure of an atom based on the information provided?

• Most of an atom's mass is located in a small, dense area at its center.

• An atom's mass and volume are evenly distributed.

• The rapidly moving electrons give the atom most of its mass.

• The nucleus of an atom takes up most of its volume.

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Identifying Atoms: Atomic Number and Mass

• The atomic number is the number of protons in an atom's nucleus.

• This number is unique and determines the identity of an element.

• Atomic mass is the sum of protons and neutrons in the nucleus.

• Neutral atoms have an equal number of protons and electrons.

Multiple Choice

What determines the identity of an element?

• The number of protons in its nucleus

• The number of neutrons in its nucleus

• The total number of electrons and protons

• The average mass of the nucleus

Multiple Choice

What is the relationship between an atom's particles and its atomic mass?

• By adding the mass of its protons and neutrons

• By measuring the total mass of its electrons

• By counting the number of electrons in the atom

• By finding the average number of protons

Multiple Choice

A neutral atom has an atomic number of 10 and an atomic mass of 20 amu. What must be true about this atom?

• It has 10 protons and 10 electrons.

• It has 20 protons and 20 electrons.

• It has 10 protons and 20 electrons.

• It has 10 electrons and 20 neutrons.

Building Substances: Elements, Compounds, and Molecules

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Element

• A pure substance made up of only one type of atom.

• All atoms of an element share the same atomic number.

• Examples are pure gold (Au) or a tank of helium (He) gas.

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Compound

• A pure substance with two or more different bonded atoms.

• The different types of atoms are bonded in a fixed ratio.

• An example is water (H₂O), with hydrogen and oxygen atoms.

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Molecule

• A structure formed when two or more atoms are chemically bonded.

• It can be made of the same element, like in oxygen gas (O₂).

• It can also be made of different elements, like carbon dioxide (CO₂).

Multiple Choice

What defines a substance as an element?

• They are made up of only one type of atom.

• They consist of two or more different bonded atoms.

• They are formed from elements in a fixed ratio.

• They can be made of the same or different elements.

Multiple Choice

How does a compound relate to a molecule?

• A compound consists of different elements bonded together, while a molecule can consist of either same or different elements bonded together.

• A molecule must have a fixed ratio of atoms, but a compound does not.

• A compound is a pure substance, but a molecule is not.

• A molecule is made of one type of atom, while a compound is made of two or more.

Multiple Choice

Using the information provided, which statement correctly classifies both water (H₂O) and oxygen gas (O₂)?

• Water (H₂O) is a compound and a molecule, while Oxygen gas (O₂) is a molecule but not a compound.

• Both H₂O and O₂ are compounds because they contain multiple atoms.

• O₂ is a compound because it is a gas, while H₂O is a molecule because it is a liquid.

• Both H₂O and O₂ are elements because they are pure substances.

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Structure of Solids: Crystalline vs. Amorphous

Crystalline Solids

• ​Atoms or molecules are arranged in a neat, highly ordered, and repeating pattern.

• ​​This organized internal structure is known as a crystalline lattice.

• ​A common example of a substance with a crystalline structure is table salt.

Amorphous Solids

• ​The atoms or molecules in these solids have no specific order or arrangement.

• ​​The particles are jumbled together in a random pattern with no repeating structure.

• ​Glass is a common example of an amorphous solid.

Multiple Choice

What is the defining characteristic of a crystalline solid?

• Its atoms are arranged in a highly ordered and repeating pattern.

• It is always made of a single type of element.

• It can be easily melted into a liquid.

• It is found only in natural minerals like glass.

Multiple Choice

How does the arrangement of particles in an amorphous solid like glass differ from that in a crystalline solid like table salt?

• Amorphous solids have a random particle arrangement, while crystalline solids have an ordered one.

• Crystalline solids are always heavier than amorphous solids.

• Amorphous solids are made of molecules, while crystalline solids are made of atoms.

• Crystalline solids are common, while amorphous solids are extremely rare.

Multiple Choice

A scientist is examining a new solid material. Under a powerful microscope, they observe that its atoms are jumbled together randomly and there is no evidence of a crystalline lattice. What is the most logical conclusion about this material?

• The material is an amorphous solid because it lacks an ordered internal structure.

• The material is a crystalline solid because all solids have a lattice.

• The material must be a liquid because its particles are not organized.

• The material is likely table salt because it is a common solid.

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Common Misconceptions About Atoms

Misconception	Correction
Atoms are flat, 2D systems with electrons orbiting a nucleus.	Atoms are 3D structures with electrons in a 3D electron cloud.
An atom's mass is distributed evenly among all its particles.	Almost all mass is concentrated in the nucleus.
Substances made of the same elements are the same.	The ratio of atoms is critical, like in H

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Summary

• All matter is composed of atoms, the fundamental building blocks of elements.

• Atoms have a positive nucleus and an element’s identity is its atomic number.

• An atom’s mass is its protons and neutrons; atoms bond to form molecules.

• Solid matter can have a crystalline or a disordered amorphous structure.

Poll

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

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