The atomic model
The electron, the proton, and the neutron gather together into what can be called the atom.
Our concept of the atom derives from a series of observations. As a result of these observations, we now believe that an atom is composed of a cloud of electrons that revolve about a central core of protons or of protons plus neutrons. Repeated experiments, which were referred to above, show that every atom has the same number of electrons as well as protons. The positively charged protons form the nucleus of the atom, and balance the positive charges of the protons in the core of the atom. The neutrons are also found in the nucleus of the atom.
An atom has already been spoken of as the smallest unit of an element.
It is known that ninety-two elements occur in nature, and a number of others have been made by man in the laboratory. Every element is a special combination of protons, neutrons, and electrons. Each element is identified by the number of protons in its nucleus and is designated by a name and a symbol.
Element Number 1 is a combination of one proton and one electron. Long before its atomic structure was known, this element was referred to as hydrogen, or "water-former", because water forms when hydrogen burns in air. Its symbol is H. Hydrogen has first place in the list of elements because it has one proton in its nucleus. Element 1 is followed by Element number 2. It consists of two protons and two electrons. It was named helium, with the symbol He.
Task 6. Work in pairs. Render the following questions into English and answer them.
1. Что такое атом?
2. Почему атом нельзя увидеть невооруженным глазом?
3. Какие методы используются для определения размеров атомов?
4. Что такое радиус атома?
5. Почему элемент № 1 называют "создателем" воды ("water-former")?
6. Из каких частей (structural units) состоит атом?
7. Где располагаются электроны?
8. Как вычислить количество электронов, протонов и нейтронов в атоме?
9. Сколько элементов существует в природе?
10. Сколько уже получено искусственных элементов?
Task 7. Discuss your plans and choose the best one. Be ready to retell the text, using your plans as tips.
Task 8. Divide into two teams. Try to match the columns as quick as possible. Who is the winner?
|
1. like 2. because of 3. closely 4. to result in 5. to pay attention 6. nucleus 7. the same charge 8. nuclei 9. means 10. meaning |
a. тщательно b. приводить c. обращать внимание d. ядро e. ядра f. тот же заряд g. средство h. значение i. из-за j. подобный |
Task 9. Read the text without a dictionary and entitle it. Explain your choice. Make a short summary of the text
The physicist Ernest Rutherford proposed a model of the atom known as planetary model. Rutherford directed the famous experiment done by Geiger-Marsden in 1910. Upon analysis of his experiment in 1911, he suggested that the plum pudding model of J.J. Thomson of the atom had drawbacks. Rutherford's new model for the atom, based on the experimental results, contained the new features as follows:
High central charge was concentrated into a very small volume in comparison to the rest of the atom and
This central volume also contained most of the atomic mass of the atom. This region was named the "nucleus" of the atom in later years.
Rutherford's model did not make any new headway in explanation of the electron-structure of the atom. Rutherford's paper merely mentioned the earlier 1904 "Saturnian" atomic model of Hantaro Nagaoka in this regard, in which a number of small electrons circled the nucleus like the particles then speculated to make up the ring around Saturn. Rutherford's concentration of most of the atom's mass into a very small core, made some type of planetary model, as such a core would contain most of the atom's mass, similar to the Sun containing most of the solar system's mass. Rutherford's model was later improved and quantified by one of his students, Niels Bohr, with the known Bohr model of the atom.
Rutherford was able to calculate that the radius of his gold central charge from purely energetic considerations of how far particles of known speed would be able to penetrate toward a central charge of 100e. He founded that it would need to be less (how much less could not be told) than 3.4 x 10-14m. This was in a gold atom known to be 10 − 10 metres or so in radius – a very surprising finding since it implied a strong central charge less than (1/3000)th of the diameter of the atom.
The Rutherford model served to concentrate a great deal of the atom's charge and mass to a very small core. But he could not contribute for any structure of the remaining electrons and remaining atomic mass. It mentioned the atomic model of Hantaro Nagaoka, which proposed that the electrons are arranged in one or more rings, with the specific metaphorical structure of the stable rings of Saturn.
Rutherford’s discovery has contributed a lot in the field of modern science. After Rutherford's theory, scientists started to consider that the atom is not a single particle ultimately, but it is made up of very smaller subatomic particles. Following research was done to figure out the exact atomic structure which led to Rutherford’s gold foil experiment.
|
|
|
|
They discovered eventually that atoms have a positively-charged nucleus (with an exact atomic number of charges) in the center Since electrons were found to be even smaller, this concluded that the atom consists of mostly empty space.
Afterwards, by using X-rays scientists found the expected number of electrons (equal to the atomic number) in an atom. When an X-ray passes through an atom, some of the rays is scattered and the rest passes through the atom. As the X-ray loses its intensity mainly due to scattering at electrons, the number of electrons contained in an atom can be accurately estimated by noting the rate of decrease in X-ray intensity.
Task 10. Make a short summary of the text using the following expressions
The given text can be entitled …
The main idea of it is to tell about …
It can be logically divided into … parts
In the first part we learn about …
The second is devoted to …
This text can be useful for …