Under the magnifying glass, students will see that the particles of various substances are crystal clear and have their own consistent geometric shapes. For example, the crystals of salt and sugar are cubes, and the crystals of monosodium glutamate are columns. On this basis, guide students to understand crystals: the particles of sugar, salt, alkaline noodles and monosodium glutamate are all composed of regular geometric bodies, and people call these substances crystals.

Then the textbook introduces the crystals in nature to students through pictures. The photos on page 8 are crystals such as crystal, snowflake, vitamin C and chalcopyrite. The shape of the crystal is very regular, some are cubes, some are like pyramids, and some are like clusters of needles; Some crystals are larger and visible to the naked eye, while others are smaller and can only be seen under a magnifying glass or microscope. Because the crystal shapes of various substances are basically the same, crystals are also the basis for identifying minerals. Geologists often observe the crystals in rocks under a magnifying glass or microscope to judge their mineral composition, so as to identify rocks. The picture on the top right of page 8 shows three kinds of crystals in granite: quartz, feldspar and mica under the microscope.

Part II: Making Crystal

Some crystals in nature are born from solutions, such as salt crystals obtained by evaporation of seawater. Some crystals are formed under certain pressure and temperature, such as mineral crystals formed after volcanic eruption and magma cooling. We can guide students to make crystals by reducing water and cooling down. Moisture reduction method, that is, air-drying the solution, even if its moisture evaporates, so that the substance is re-precipitated; Reduce the temperature, that is, first heat the solution of a substance to make a saturated solution, and then cool it to re-precipitate the substance. The production method introduced in the textbook is evaporation, that is, the substance is first made into a solution, and then a drop is dropped on the glass slide to allow it to evaporate naturally.

The crystals made by this method are relatively small, and a method of making larger crystals is also introduced in the textbook. In a large glass, add more water and salt until all the salt is dissolved. Filter the solution with a funnel, pour the filtered solution into a clean glass, hang a thin thread in the glass, tie a small piece of salt crystal at one end and soak it in the solution, and then let it stand for a few days. The first batch appeared at the bottom of the glass.

Crystal, filter out the residual crystal in the solution, and then soak the crystal hanging on the thin line in the filtered solution, and the crystal will

Grow up slowly. If people continue to pour saturated salt solution into cups, crystal growth will last for weeks or even months.

(D) Teaching suggestions

1. Observe the beautiful crystal.

Students have observed the crystals of minerals in the fourth grade, and teachers can cut people from here. Show me some more minerals.

Pictures of crystals such as crystal, pyrite and calcite. Ask the students if they remember what this is. What are their shapes?

Features (with relatively regular geometry).

Then the teacher went on to say that in addition to the regular geometry of minerals, many objects in nature also have such knots.

Structure, do we know? Sugar, salt and alkaline noodles are the materials we often use in cooking. Today, let's take a closer look.

Observe their morphology carefully.

Followed by student observation activities in groups. Let the students observe the sugar, salt and alkali surface with the naked eye, and then observe it with a magnifying glass.

Check them and see what they are like. It is necessary to observe not only the shape of each particle, but also all particles of the same substance.

The shape of. And draw the crystal shapes of sugar, salt, alkaline noodles and monosodium glutamate on the record sheet.

On the basis of students' reports and exchanges, the teacher asked the students to summarize the characteristics of particles in these objects. Last teaching

Teacher's summary: salt, sugar, monosodium glutamate and alkaline surface can be seen under the magnifying glass. Although the shapes are different, they are all the same.

Matter particles have regular geometric shapes. People call this substance crystal.

Then the teacher asked the students, they also know what crystalline substances are in nature. Except the students' answers and textbooks.

As shown in the picture, teachers can also make supplements, such as scale in water containers. And tell the students that there are many in nature.

Solid substances are all crystals, but most of them are invisible to our naked eyes. We can only see them under a magnifying glass or microscope.

For example, if you look at three kinds of mineral crystals in granite, we observe them with a magnifying glass. Their shapes are not very clear. This is

It must be observed under a microscope. When geologists identify rocks and minerals, they often make them according to their crystal forms.

Judge.

Crystals have three characteristics:

(1) crystals have regular geometric shapes;

(2) The crystal has a fixed melting point, and the temperature remains constant during the melting process;

(3) The crystal is anisotropic.

I hope it helps you.

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