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

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

Text: “Atomic Structure and Quantum Theory”.

At the turn of the 20^th century, physicists spent much effort in trying to derive all the observed phenomena relating to elements from a mathematical model of the atom. One key phenomenon was the spectral lines produced by atoms on being heated: each element has its own unique atomic spectrum. In trying to explain the generation and appearance of atomic spectra, physicists found that they had to introduce the concept of quantum.

Close scrutiny of a black-and-white newspaper photograph reveals that the apparent differences in light and dark tones are not the result of gradual shading but rather are created by subtly different sizes of dots, or “packets” of ink on the plain paper. Physicists have discovered that, in dealing with matter on the smallest scale, even energy must be treated as existing in “packets” or quanta, and not as being continuous. The quantum concept provides the key to understanding how atoms can absorb and emit energy, and how the various atomic spectra are produced.

In a simple quantum-based visualization of the atom, the electrons orbit the central nucleus like planets in a miniature solar system. The electrons can move only in certain orbits about the nucleus. By giving up that energy, they drop back into the original lower orbits (called the ground state). With each energy change, radiation of a particular frequency is absorbed or emitted.

From this analysis, the origin of atomic spectra can be explained. The individual spectral lines (of certain frequencies) represent electrons falling from high-energy excited states back to their low-energy ground states. As they do so, they emit quanta of radiation (photons).

III. Put the sentences in the right order.

1. In an atom the electrons orbit the central nucleus like planets in a miniature solar system.
2. In trying to explain the generation of atomic spectra, physicists introduced the concept of quantum.
3. The individual spectral lines represent electrons falling from high-energy excited states back to their low energy ground states.
4. At the beginning of the 20^th century scientists tried to derive all the observed phenomena from a mathematical model of the atom.
5. The quantum concept provides the key to understanding how atoms can absorb and emit energy.

IV. Translate the following noun groups into Russian. 

1. key phenomenon;                             
2. energy change;
3. the appearance of spectra;               
4. the concept of quanta;                      
5. the study of a photograph;              
6. different sizes of dots;                      
7. “packets” of ink;
8. a visualization of the atom;
9. a miniature solar system;
10. radiation of a particular frequency
11. the origin of atomic spectra;
12. quanta of radiation.

V. Find Russian equivalents to the following expressions in the text. 

1. spent much effort;                                         
2. its own unique atomic spectrum;                  
3. in dealing with matter on the smallest scale;
4. the result of gradual shading;                        
5. the concept of quantum;
6. the quantum concept;
7. the ground state
8. emit quanta of radiation.