"Molecules and Atoms" The Mystery of Material Composition PPT Courseware 8

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"Molecules and Atoms" The Mystery of Material Composition PPT Courseware 8

Lesson 1: Matter is composed of microscopic particles

Why can people be intoxicated by the refreshing fragrance of flowers when walking in the garden?

[Experiment] Magenta diffuses in water

1. Why does magenta diffuse in still water?

Magenta particles move in water and continue to diffuse, causing the solution to turn red.

2. Magenta diffuses quickly in hot water. Why?

When the temperature is high, the particles move faster and the solution turns red faster.

【Explore】Molecular motion phenomena

1. Add 5-6 drops of phenolphthalein solution to beaker A containing about 20mL of distilled water, stir evenly, and observe the color of the solution.

Phenomenon The solution is colorless

Conclusion Water cannot change the color of phenolphthalein, but only plays a diluting role.

2. Take a small amount of solution from beaker A and place it in a test tube, add concentrated ammonia slowly and dropwise into it, and observe any changes in the color of the solution.

Phenomenon: The color of the solution changes from colorless to red

Conclusion Colorless phenolphthalein turns red when exposed to concentrated ammonia

3. Take another small beaker B and add 5 mL of concentrated ammonia. Use a large beaker to cover two small beakers A and B. Observe for a few minutes. What happens? What does this phenomenon indicate?

Phenomenon: The solution gradually turns red, but the solution does not change color.

Explain that the ammonia molecules in B are constantly moving into beaker A, making the phenolphthalein solution turn red (indicating that the molecules are always in constant motion)

Summary: Characteristics of Molecules

⒈The mass and volume of molecules are very small;

⒉ Molecules are always in constant motion;

⒊There are gaps between molecules.

4. Molecules of the same substance have the same properties, while molecules of different substances have different properties.

Give it a try:

1. When water freezes into ice, the result is ( )

A. The size of water molecules changes

B. The distance between water molecules has changed

C. The color of water molecules changes

D. The chemical properties of water molecules change

2. Use molecular knowledge to explain the following phenomena in life, which one is wrong ( )

A. Thermal expansion and contraction, indicating that the size of molecules changes as the temperature rises and falls.

B. "The aroma of wine is not afraid of the depth of the alley", indicating that the molecules are constantly moving

C. After mixing 10mL alcohol and 10mL water, the volume is less than 20mL, indicating that there is a gap between the molecules.

D. Wet clothes are easier to dry in summer than in winter, indicating that the movement rate of molecules accelerates as the temperature increases.

【Learning Summary】:

The concept of "molecule": a substance composed of molecules, which are the smallest particles that maintain their chemical properties.

Expand and extend:

⑴Premise: The substance should be composed of molecules;

⑵ "Maintain" means that each molecule that makes up the substance is consistent with the chemical properties of the substance;

⑶ Molecules can only maintain the chemical properties of the substance, but not its physical properties, because the physical properties of a substance are manifested by the aggregation of a large number of molecules (macroscopic phenomenon).

⑷ "Smallest particle" is considered from the perspective of "maintaining the chemical properties of matter", rather than simply saying that molecules are the smallest particles.

1. A molecule is a particle that constitutes a substance. For example, water, hydrogen peroxide, ammonia, carbon dioxide, mercury oxide are composed of molecules, etc.

2. Molecules are composed of atoms. Some molecules are composed of the same kind of atoms. For example, an oxygen molecule is composed of 2 oxygen atoms. A hydrogen molecule is composed of 2 hydrogen atoms.

3. Most molecules are composed of two or more kinds of atoms. For example, a carbon dioxide molecule is composed of 1 carbon atom and 2 oxygen atoms; an ammonia molecule is composed of 1 nitrogen atom and 3 hydrogen atoms. constituted.

1. Multiple choice questions:

1. The following smallest particles that can maintain the chemical properties of oxygen are ( )

A. Oxygen molecules B. Oxygen atoms

C. Oxygen ions D. Oxygen

2. Which of the following statements about molecules and atoms is correct ( )

A. Hydrogen peroxide decomposes to produce water and oxygen, which means that hydrogen peroxide contains water molecules and oxygen molecules;

B. The molecular chemical properties of the same substance are the same, while the molecular chemical properties of different substances are different;

C. Matter is made up of molecules, and molecules are made up of atoms.

D. The same kind of atoms can form molecules, but different kinds of atoms cannot form molecules.

Summary of this topic

1. Matter is composed of microscopic particles such as molecules and atoms.

2. Properties of microscopic particles:

⑴The mass and volume of molecules are very small;

⑵Microscopic particles (such as molecules and atoms) are always in constant motion;

⑶There are gaps between molecules;

⑷The molecules of the same substance have the same properties, while the molecules of different substances have different properties.

3. Concepts of molecules and atoms:

1. A substance composed of molecules, which are the smallest particles that maintain their chemical properties.

2. Atoms are the smallest particles in chemical changes.

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Update Time: 2024-11-22

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