UNIT 4

 

I. Find out the words in the dictionary. Write them down and learn.

 

to possess, cohesion, attractive forces, rigid, repulsive forces, to retain, crystalline,  amorphous, to melt, lattice, a melting point, however, negligible, to repel, to approach, because of, to cause, to vibrate

 

II. Read the text. Use a dictionary, if necessary.

 

Text: “States of Matter”.

 

All substances can, under the right conditions, exist as a solid, liquid, or gas. These are the three basic physical states (or phases) of matter.

Solids possess the property called cohesion; that is, their component particles (atoms or molecules) are held together by attractive forces. As a result, solid substances are rigid and retain their shape unless deformed by external forces.

There are two principal types of solids: crystalline and amorphous. Crystalline solids have definite crystalline structures. Most also melt at specific temperatures to become liquids. Examples include metals, ice, and many plastics, in addition to obviously crystalline substances such as common salt and diamond. In contrast to crystalline solids, amorphous solids have neither crystalline structures nor specific melting points. Glass is an example of amorphous solids.

Liquids represent the intermediate stage between solid and gas. A liquid’s atoms or molecules have some degree of cohesion and so tend to remain together. But they are not rigidly linked and can therefore move in relation to each other – which is not possible in solids. For this reason liquids flow and in a gravitational field take on the shape of the vessels in which they are contained.

In a gas the constituent particles have negligible cohesion and can therefore move almost completely independently of each other. Like liquids, gasses flow and assume the shape of their containers. Unlike liquids, however, gasses always fill the entire space in their containers – and the container needs to be closed if the gas is not to escape.

The attractive forces between atoms or molecules in a solid are balanced by repulsive forces. As two of these particles approach each other, the outer electrons of one repel the outer electrons of the other, and the atoms or molecules move apart. But because of the attractive forces between them, they move back toward each other again. The overall result of the attractive and repulsive forces is to cause each of the atoms or molecules in a solid to vibrate continually about the same position in a lattice.

The atoms or molecules of a liquid are also affected by attractive and repulsive forces. But a liquid is hotter than the same substance in solid form and its vibrating particles therefore have greater kinetic energy – that is, they vibrate more violently. As a result, the attractive forces cannot hold them in a lattice, and they are relatively free to move.

In a gas the atoms or molecules have so much energy that they have largely broken free of the influences of the attractive and repulsive forces and, therefore, have almost complete freedom of movement.

 

III. Translate the words of the same root. Define parts of speech.  

 

to exist – existence – existent

obvious – obviously – obviousness

molecule – molecular – intermolecular

to attract – attraction – attractive

violent – violently

to move – movement

atom – atomic – interatomic

to shape – shape – shapeless – shapelessness 

relativity – relative – relatively

to add – addition

definite – definitely – indefinitely

to form – formation – deformation 

complete – completely – completeness

to assume – assumption

to depend – dependence – dependent – independent – independently

to contain – container

entire – entirely

to specify – specific – specifically – unspecified

possible – impossible

 

IV. Practice the following speech patterns.

 

Pattern 1.  Atoms move in relation to each other.

 

1. Molecules	3. People	5. Neutrons	7. Electrons
2. Particles	4. Planets	6. Protons

 

Pattern 2.  Solids possess the property called cohesion.

 

VIII. Fill in the missing words.

 

1. All substances can ___ as a solid, liquid or gas.
2. Solids possess the ___ called cohesion.
3. In solids the component particles are held together by ___ forces.
4. Crystalline solids have ___ ___ structures.
5. Most solids ___ at specific temperatures to become liquids.
6. Amorphous solids have neither crystalline structures nor ___ ___ points.
7. In a gas the constituent particles have ___ cohesion.
8. Like liquids, gasses flow and ___ the shape of their containers.

 

IX. Fill in the prepositions if necessary.

 

1. In a gas the particles can move almost completely independently ___ each other.
2. The attractive forces between atoms or molecules ___ a solid are balanced ___ repulsive forces.
3. As two of the particles approach ___ each other, the outer electrons of one repel the outer electrons of the other, and the atoms or molecules move ___ .
4. Because of the attractive force between them, they move ___ ___ each other again.
5. In a gas the atoms or molecules have so much energy that they have largely broken free ___ the influences ___ the attractive and repulsive forces.

 

X. Practice with someone asking and answering.

 

1. In what forms can all single substances exist?
2. What main property do solids possess?
3. What do we mean by cohesion?
4. What are two principal types of solids?
5. Crystalline solids have definite crystalline structures, don’t they?
6. Do they melt at specific temperatures?
7. What are the examples of crystalline solids?
8. Do amorphous solids have crystalline structures and specific melting points?
9. What are the examples of amorphous structures?
10. Liquids represent the intermediate stage between solid and gas, don’t they?
11. What are the properties of liquids?
12. Why do liquids flow?
13. Do the constituent particles in a gas have any cohesion?
14. Do gases behave like liquids? Are gases similar to liquids?
15. Are the attractive forces between atoms or molecules in a solid balanced by other forces?
16. What is the overall result of the attractive and repulsive forces in a solid?
17. Are the atoms or molecules of a liquid also affected by attractive and repulsive forces?
18. Why are the atoms or molecules in a gas free of the influences of the attractive and repulsive forces?

 

XI. Put questions to the following sentences.

 

1. Crystalline solids have definite crystalline structures.  (General)
2. Glass and many resins are examples of amorphous solids.  (Alternative)
3. The attractive forces cannot hold particles in a lattice.  (Disjunctive)

 

XII. Dictate the following sentences in English to your fellow-students. Check them together.

 

1. All single substances can exist as a solid, liquid, or gas.
2. Crystalline solids have definite crystalline structures.
3. Most solids melt at specific temperatures to become liquids.
4. A liquid’s atoms or molecules have some degree of cohesion and so tend to remain together.
5. Liquids flow and in a gravitational field take on the shape of the vessels in which they are contained.
6. The overall result of the attractive and repulsive forces is to cause each of the atoms or molecules to vibrate continually about the same position in a lattice.
7. A liquid is hotter than the same substance in a solid form and its vibrating particles have greater kinetic energy.

 

XIII. Dictation-translation.

 

1. Существует три физических состояния материи.
2. Твердые тела обладают свойством, называемым связность, т.е. их составляющие удерживаются вместе силами притяжения.
3. Существует два основных вида твердых тел: кристаллические и аморфные.
4. Жидкости представляют собой промежуточную ступень между твердым телом и газом.
5. Атомы жидкости не являются жестко связанными между собой и могут двигаться относительно друг друга.
6. В газе составляющие его частицы имеют незначительную связность и могут двигаться почти полностью независимо друг от друга.
7. Силы притяжения между атомами и молекулами в твердом теле уравновешиваются силами отталкивания.