Topicme2485ffd59a6bdad_1528449000663_0Topic

Intermolecular interactions

Levelme2485ffd59a6bdad_1528449084556_0Level

Second

Core curriculumme2485ffd59a6bdad_1528449076687_0Core curriculum

I. Using physical terms and quantities to describe phenomena and to identify their examples in everyday life.

Timingme2485ffd59a6bdad_1528449068082_0Timing

45 minutes

General learning objectivesme2485ffd59a6bdad_1528449523725_0General learning objectives

Identifying intermolecular interactions and their results.

Key competencesme2485ffd59a6bdad_1528449552113_0Key competences

1. Recognising intermolecular interactions.

2. Determining the magnitude of intermolecular interactions in different states of matter.

Operational (detailed) goalsme2485ffd59a6bdad_1528450430307_0Operational (detailed) goals

The student:

- identifying intermolecular interactions,

- specifying what determines the magnitude of interactions.

Methodsme2485ffd59a6bdad_1528449534267_0Methods

1. Learning through observation.

Forms of workme2485ffd59a6bdad_1528449514617_0Forms of work

1. Individual work.

2. Work with the whole class.

Lesson stages

Introductionme2485ffd59a6bdad_1528450127855_0Introduction

Molecules are constantly interacting with each other. These impacts are complex. Some of the physical properties of the bodies, such as e.g. states of matter, are a direct consequence of the interactions.
When molecules are too close to each other, i.e. at distances close to their diameter or smaller, a very strong repulsive effect prevails. At distances greater than the diameter of the particles, the attracting effect begins to dominate. In solids that exhibit intense intermolecular interactions, the described phenomena cause the particles approach each other and can only vibrate around their equilibrium positions.me2485ffd59a6bdad_1527752263647_0Molecules are constantly interacting with each other. These impacts are complex. Some of the physical properties of the bodies, such as e.g. states of matter, are a direct consequence of the interactions.
When molecules are too close to each other, i.e. at distances close to their diameter or smaller, a very strong repulsive effect prevails. At distances greater than the diameter of the particles, the attracting effect begins to dominate. In solids that exhibit intense intermolecular interactions, the described phenomena cause the particles approach each other and can only vibrate around their equilibrium positions.

[Illustration interactive]

Procedureme2485ffd59a6bdad_1528446435040_0Procedure

Look at the experiment the teacher has made.

Experiment 1 (demonstration)

Research problem:me2485ffd59a6bdad_1527752256679_0Research problem:

Presentation of intermolecular interactions.me2485ffd59a6bdad_1527752256679_0Presentation of intermolecular interactions.

Research hypothesis:

Between two planes there occur intermolecular interactions depending on the distance between the moleculesmoleculesmolecules of the surfaces in contact. The presence of an intermediate liquidliquidliquid layer can affect the adhesionadhesionadhesion forces of the two contacting surfaces.

The procedure of the experiment:

1. The teacher presses two optical disks putting sides with a label towards each other and then checks if there is a clear interaction between the surfaces of the optical disks.

2. The teacher applies some water (with a brush) onto the surface with the label of one of the optical discs (illustration 1 and illustration 2) and presses the second optical disc (the surface with the label) to the first one. After squeezing the excess water from the gap between the disks, the teacher raises the upper disk, which lifts the lower disk with adsorption forces (illustration 3) (in this case these forces are adhesionadhesionadhesion ones).

[Illustration 1]

[Illustration 2]

[Illustration 3]

Conclusion:

In the case of dry surfaces, the strength of their interaction is very small. Both surfaces are not perfectly flat and have unevenness, which results in the fact that the effective contact area between both surfaces is a fraction of a percent of the entire surface. After wetting the surface, squeezing the air and soaking the mirror, the effective contact surface of both surfaces increases. The intermediate medium between the two surfaces is water, whose moleculesmoleculesmolecules strongly interact with each other. The strength of these interactions is much greater than that in the gasgasgas that previously filled the gaps between the surfaces of the covers of the optical disc. This force is called the adhesionadhesionadhesion force. The experiment proves that the magnitude of intermolecular interactions depends on the average distance between the moleculesmoleculesmolecules of the physical body.

Lesson summaryme2485ffd59a6bdad_1528450119332_0Lesson summary

- MoleculesmoleculesMolecules constantly interact with each other. Intermolecular interactions occur between moleculesmoleculesmolecules or atoms of liquidliquidliquid, gasgasgas and solids. If the distances between the moleculesmoleculesmolecules are close to their diameter or smaller, the interaction is repulsiverepulsiverepulsive and if these distances are greater, the attractingattractingattracting effect dominates.

- The movement of moleculesmoleculesmolecules in the solids is the least free, i.e. they vibrate around certain positions of their equilibrium and the intermolecular interactions are the strongest.

- In liquids, the moleculesmoleculesmolecules move more freely and more quickly than in solids.

- In gases, the interactions between the moleculesmoleculesmolecules are the weakest. GasgasGas moleculesmoleculesmolecules have high velocities and the freedom of movement.

Selected words and expressions used in the lesson plan

adhesionadhesionadhesion

attractingattractingattracting

gasgasgas

liquidliquidliquid

moleculesmoleculesmolecules

repulsiverepulsiverepulsive

solidsolidsolid