Some facts about atoms (I)
An atom may be spoken of as the smallest partiole of any substance. If atoms cannot be seen it does not necessarily mean that they do not exist. It indicates that any particle, if present, must be extremely small. There are methods by means of which the sizes of atoms and their arrangement in molecules can be determined. One of these methods uses X-ray diffraction.
The results
of a number of investigations show that when atoms are in contact
with other atoms in molecules, their radius is as much as
0,1·
m(0,1nm).
Some idea of how small atoms are can be obtained by imagining one million copper atoms/radius= 0,13· m (0,13 nm). If these copper atoms are stacked one on the top of the other, the pile will be as high as the full stop at the end ot this sentence.
In the course of many investigations, chemists came to a conclusion that the atoms of different elements are all made essentially of three simple types of units, which were referred to as protons, neutrons, and electrons.
The following diagram shows us the constituents of the atoms Atoms contain the following structural units:
Electrons Protons Neutrons
Charge –1, Charge +1, Zero charhe,
very small relative relative mass 1 relative mass 1
mass
Notes on the text:
a full stop - точка in the course of - в ходе, процессе
Words to be remembered:
particle by means of
neoessary arrangement
to mean conclusion
to indicate constituent
extremely charge
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Some facts about atoms (II)
The position and numbers of these structural units in an atom is shown below:
Electrons
fill the space around nucleus. Number of electrons = Atomic number.
Vary small nucleus. Number of protons = Atomic number. Number of
protons + Number of neutrons = Relative atomic mass.
The numbers of electrons, protons, and neutrons in an atom of an element can be calculated if the atomic number and relative atomic mass of the element are known:
Number of electrons + Number of protons = Atomic number of element.
Number of protons + Number of neutrons =Relative atomic mass of element.
It was also found that many elements and compounds are composed of small numbers of atoms which are held together in a regular arrangement. These groups of atoms are referred to as molecules. The gas hydrogen, for example, is composed of pairs
of hydrogen atoms and each pair is called a molecule and its formula is H2.
Another example is the compound carbon dioxide which is composed of molecules, the formula is CO2.
Words to be remembered:
space to be composed of
nucleus hydrogen
relative carbon dioxide
calculate
Note on the text:
regular arrangement - упорядоченное расположение
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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. 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 bums 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 £allowed by Element Humber 2. It consists of two protons and two electrons. It was named helium, with the symbol He.
Words to be remembered:
concept to identify
revolve to designate
core to refer to
as well as to burn
to balance to occur
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