1.1An Introduction to Kinetic Molecular Theory

QUI_01_ Physico-chemical assays of solids
AF Unit 1: Physico-chemical properties of solid substances

1.1An introduction to kinetic molecular theory

Source: es.wikipedia.org

The kinetic molecular theory explains the behavior of solids, liquids and gases. Have you ever wondered why these substances behave so differently?

Look at the image. Why is it possible for water to be solid, liquid or gas? What differences do you find between the microscopic structure of a solid and a liquid?

Some of you may remember the answer from previous courses. In case you haven’t heard about the kinetic molecular theory, go to the following animations that will help you understand the basics of this important scientific theory. Notice you can activate subtitles in the animation in case you need it:

/ Interactive content: Behavior of Matter
/ Interactive content: The Particle Model

TASK 1: Do the following online tests to check if you understood the kinetic theory.

/ Test: Behavior of Matter
/ Test: The Particle Model

TASK2: You are given sentences that describe the behavior of a substance. You have to decide if the sentence describes a solid, a liquid or a gas. Then, check your answers with your partner.

Any attractions between the particles are fairly negligible.
The particles are mainly touching, but some gaps have appeared in the structure.
The particles are touching and the only motion allowed to them is vibration.
The distance between individual particles is of the order of ten times the diameter of the particles.
The particles are arranged regularly or at random.
The particles are entirely free to move.
The particles are almost as close together as they were in a solid.

TASK 3: The following online-tests are a little bit more difficult. Work in pairs and help each other. Write down your score for each test:

/ Review quiz: kinetic molecular theory. Score:______.
/ Practice quiz: kinetic molecular theory. Total points:______out of 15.

1.2 Basics about solid substances

In this formative activity, you will get to know more about solids, liquids and gases. Nevertheless, you are going to focus your attention on solid substances.

Don’t worry if you don’t understand some English words. You can always check the following website to translate them into your own language. Be careful with online translators, sometimes they can make mistakes when translating sentences out of context:

/ Free online translator

TASK 4: Use the following substitution table to produce three correct sentences about solids. See the example below:

Solid substances / melt / because / their molecules are ordered
Like ionic chemical compounds are crystalline / a quantity of heat is applied
have a definite shape / its molecules are fixed in their places by intermolecular forces

“Solid substances melt because their molecules are ordered”. The sentence is written taking one part of each of the columns. (by the way, is the sentence in the example correct?)
______
______
______

TASK 5: Check the answers of “task 4” with your partner. Have you written the same sentences?

1.3 Microscopic structure of solid substances

Look at the following image:

Source: cristalchornet.blogspot.com

The image shows two different solid structures. It is important that you are able to distinguish between these two kinds of solids.

HIGHLIGHTS
On the left side of the image, atoms are located at random positions. These kind of solid structures are called amorphous. On the right side of the image, atoms are arranged regularly; these kinds of solids are crystals.

TASK 6:You will work in pairs. The following link takes you to an interesting video in which you can see different molecular structures of solid substances.

/ Molecular structuresof solid substances

To learn vocabulary about solid structures and understand the difference between crystalline and amorphous solids, try to complete the following text, which is a transcription of the video.

Use the following words to fill in the gaps:

Remember that you can always use an online translator if you don’t know the meaning of some of the words.

/ Free online translator

Crystalline and amorphous solids

There are two main classes of ______, crystalline and amorphous.

Crystalline solids: observe the ______of the solid displayed on the screen. You can easily trace the regular ______pattern of the atoms or the molecules or ions. These type of solids are called ______solids. The crystalline solids have symmetrical shapes flat smooth and plain faces which meet at a characteristic angle. Crystalline solids are classified as “single crystals” and “polycrystalline crystals”. If the periodicity of the pattern is extended throughout the volume of the solid, then the solid is a ______crystal. In a polycrystalline crystal, the periodicity of the pattern is ______at de boundaries. Crystalline solids have a sharp ______point. All ______have the same strength in the case of crystals. Diamond, rock salt, mica and ______belong to this category.

Amorphous solids: like______, the atoms and the molecules of amorphous solids are not arranged in an orderly manner, but the difference between an amorphous solid and a liquid is that the ______are ______fixed and they are not free to move as in liquids. ______is an amorphous solid.

TO KNOW MORE
Crystalline solids can have different kinds of crystalline structures, depending on how the molecules or atoms are ordered. Check the following link to learn more about these structures.
/ Types of crystals

1.4 Polar and non-polar substances. Solubility.

Molecules can be classified in polar and non-polar. This is important to determine, for instance, if a solid is soluble in a liquid. As a general rule, remember the following sentences:

HIGHLIGHTS
A general rule is that like dissolves like.
Generally, ionic and polar substances are soluble in polar solvents like water.
Non-polar compounds are normally soluble in non-polar solvents such as carbon tetrachloride.

TASK 7: Now it’s time to write some questions and test your partner’s knowledge about solubility and polarity of solvents and solutes. Make groups of two. First of all, read the following information about solubility:

/ Solubility. Factors affecting solubility.

If you find it difficult to write questions in English, you can use the following language support:

Then, prepare a quiz with at least 5 questions about solubility and polarity of solutes and solvents. Finally, share your quiz with other couples and try to answer quizzes prepared by your partners. Create the quiz using the following internet resource:

/ Create your own quizzes!

QUI_01_ Physico-chemical assays of solids. / Unit 1