Physics 8 Lesson 19: How are substances made?
1. Theoretical summary
1.1. Substances are made up of separate particles
– Matter is not a solid block, but substances are made up of separate particles called atoms and molecules.
Atoms and molecules are extremely small particles that cannot be seen with the naked eye.
Atoms are the smallest particles of matter, molecules are groups of atoms.
- Modern microscopes are used to observe atoms and molecules
1.2. Is there a gap between the atoms?
a) Model testing:
– An experiment similar to the required experiment is called Model Experiment
– C1: Pour 50 \(cm^3\) sand into the 50 \(cm^3\) corn container, shake gently. Comment on the volume of the mixture after mixing, compared with the total original volume?
Experimental comments: Mix 50 \(cm^3\) corn into 50 \(cm^3\) sand, the resulting mixture is less than 100 \(cm^3\) . Because there is a gap between the corn grains, when sand is poured into the corn, the grains of sand are interspersed with these gaps, making the volume of the mixture smaller than the sum of the volumes of the corn and the sand.
b) There is a distance between atoms and molecules:
– C2: Explain the volume loss of the above mixture of alcohol and water?
Experimental remarks: There is a distance between the alcohol and water molecules, so when alcohol is poured into water, the alcohol and water molecules alternate between each other, so the resulting mixture has a volume smaller than the sum of the two volumes. substance when mixed.
Atoms and molecules are so small that we can’t see them, so the above experiment is a model experiment that helps us visualize the distance between atoms and molecules.
Conclusion: There are distances between atoms and molecules of any substance.
2. Illustrated exercise
Question 1: Fish need air to live, but we can see fish can still live in water.
We see, fish can still live in the water because the air molecules can enter the gap between the water molecules.
Verse 2: Explain why an inflated rubber ball or balloon, no matter how tight it is tied, keeps getting smaller and smaller.
The wall of a rubber ball or balloon is made up of rubber molecules, there is a gap between these molecules.
⇒ Air molecules in the balloon can pass through these gaps to get out, causing the balloon to deflate.
3.1. Essay exercises
Question 1: Why does a balloon, even though it’s been tied for a long time, still deflate?
Verse 2: Why does a gas always occupy the entire volume of the container?
Question 3: Why does a liquid have a definite volume but have the shape of the container part?
Question 4: Why is sea water salty?
3.2. Multiple choice exercises
Question 1: Choose the correct statement?
A. Atoms and molecules are extremely small particles that cannot be seen with the naked eye.
B. Atoms, molecules are extremely small particles, but can still be observed with the naked eye.
C. Since atoms and molecules are very small, there is no distance between them.
D. Atoms, molecules of substances are the same.
Verse 2: Why do substances look solid even though they are all made up of separate particles? Which of the following is the most correct explanation?
A. Because matter particles are very small, the distance between them is also very small, so we can’t distinguish it with the naked eye.
B. Because an object is made up of only a handful of particles.
C. Because the size of the particles is not very small, but they are located very close to each other.
D. Another interpretation.
Question 3: Select the correct answers
A. Substances are made up of molecules, molecules are the smallest indivisible particles.
B. In the solid state, the bonding force between molecules and atoms is smaller than in the liquid state.
C. The number of molecules and atoms that make up substances is very large because the size of these particles is very small.
D. Because of the conserved volume, when two liquids are mixed, the volume of the mixture will be equal to the sum of the volumes of the two liquids.
Question 4: Choose the wrong sentence:
A. Air mixes with another gas more easily than it does with a liquid.
B. The solid completely does not allow a gas to pass through because there is no distance between the particles constituting the solid.
C. Fish can still live in rivers, lakes, ponds and seas. This shows that the oxygen in the air is dissolved in the water without changing the volume of the solution.
D. The fact that sugar dissolves in water shows that there is a distance between water molecules.
Through the lecture How are substances made? Here, you need to complete some of the goals that the lesson gives, such as:
Understand how substances are structured?
Give practical examples that show that there is a distance between molecules.
Understand the initial steps of recognizing a model experiment and showing the similarity between a model experiment and the phenomenon to be explained.