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Updated October 15, 2014

Size of atoms

See an atom of about 1 angstrom

From the Greek "atomos," indivisible, the atom is the smallest particle of a chemical element, it consists of a nucleus around which a number of moving electrons, one for hydrogen, 6 for carbon , 26 for iron, 92 for uranium, etc.
These are electron-electron interactions due to their amazing quantum properties that give rise to the wide variety of elements that we find in nature. The organization of the elements of nature is represented by the periodic table or table of Mendeleev, which classifies all natural and artificial chemical elements ordered by atomic number (number of protons) increasing and organized according to their electronic configuration.
The world of electrons, belongs to the quantum world of atoms, i.e. the microscopic world. Between the atom of the microscopic world and the macroscopic world, there is a very large number of magnitudes. In one gram of material such as carbon 12, there ≈1022 atoms.
We know the approximate size of atoms since 1811, Amedeo Avogadro (1776-1856) estimated its size to 1 angstrom, i.e. 10-10 meter and one century later, in 1911 Ernest Rutherford (1871-1937) specifies, the structure of atoms, and gives a size the atomic nucleus of the order of 10-14 meters. One can say that the atoms are separated from each other of a few angstroms.
But since the advent of quantum mechanics in the 1920s, we do not represent, the electron as a spinning object on a very regular orbit around the nucleus, as in a planetary model. Today we know that the motion of an electron is quite different from planetary motion. In quantum mechanics the electron does not follow a single trajectory, it is here and there, in a region around the nucleus called the electron cloud, or atomic orbital.
The orbitals of the electron may take different forms depending on the characteristics of the nature of atom, for example, the orbital of the hydrogen atom has a spherical shape, the orbital of the atom oxygen in the form of two drops of water, the orbital of the iron atom is in the form of four drops of water. This form of the atomic orbital sets the size of the atom.
Thus the diameter of the electron cloud around the nucleus i.e. the diameter of the whole atom is of the order of 0.1 nanometer or one ten billionth of a meter. An atom is so small that we could align 10 million atoms on a millimeter. However, the electron cloud of an atom does not have a well-defined dimension because it is a superposition of atomic orbitals of a probabilistic nature (they vary). There is therefore no single definition nor precise measure of the size of atoms because the shape of this region of atomic space depends on the energy of the electron and its angular momentum. But to get an idea of ​​the size of the atom, scientists have defined a theoretical atomic radius.

A theoretical atomic radius represents half of the average distance between the nuclei of linked atoms among themselves. Although this distance varies depending on the properties of the atom, it can be calculated for each atomic nucleus, the size of the atomic orbitals (see table). The size of the atoms increases with the number of electrons or rather according to the occupancy of the atomic orbital electrons of the outer layer, which is bonded to the nucleus far less than the inner layers. The more layers (quantum energy levels) in the atom and the more outer layer is extended, i.e. the superposition of the atomic orbitals increases the size of atoms as the outer layer is less and less related to the nuclei and therefore freer. However, the more electrons in the inner layers and the more the attraction of the atomic nucleus is growing because there is more and more protons and therefore more and more positive charges. This property (number of protons) limits the spatial extent of the atomic orbitals negatively charged (negative charges of electrons), bringing closer them to the nuclei.

Theoretical size of atoms in picometers (pm)
(1 pm = 10-12 meter)
 size size  size  size
H  Hydrogen :
number of electron by energy levels 1
53Ca Calcium :
number of electron by energy levels 2, 8, 8, 2
194Y  Yttrium :
number of electron by energy levels 2, 8, 18, 9, 2
212Hf Hafnium :
number of electron by energy levels 2, 8, 18, 32, 10, 2
208
He Helium :
number of electron by energy levels 2
31Sc Scandium :
number of electron by energy levels 2, 8, 9, 2
184Zr Zirconium :
number of electron by energy levels 2, 8, 18, 10, 2
206Ta Tantalum :
number of electron by energy levels 2, 8, 18, 32, 11, 2
200
Li Lithium :
number of electron by energy levels 2, 1
167Ti Titanium :
number of electron by energy levels 2, 8, 10, 2
176Nb Niobium :
number of electron by energy levels 2, 8, 18, 12, 1
198W  Tungsten :
number of electron by energy levels 2, 8, 18, 32, 12, 2
193
Be Beryllium :
number of electron by energy levels 2, 2
112V  Vanadium :
number of electron by energy levels 2, 8, 11, 2
171Mo Molybdenum :
number of electron by energy levels 2, 8, 18, 13, 1
190Re Rhenium :
number of electron by energy levels 2, 8, 18, 32, 13, 2
188
B  Boron :
number of electron by energy levels 2, 2
87Cr Chromium :
number of electron by energy levels 2, 8, 13, 1
166Tc Technetium :
number of electron by energy levels 2, 8, 18, 13, 2
183Os Osmium :
number of electron by energy levels 2, 8, 18, 32, 14, 2
185
C  Carbon :
number of electron by energy levels 2 ,4
67Mn Manganese :
number of electron by energy levels 2, 8, 13, 2
161Ru Ruthenium :
number of electron by energy levels 2, 8, 18, 15, 1
178Ir Iridium :
number of electron by energy levels 2, 8, 18, 32, 15, 2
180
N  Nitrogen :
number of electron by energy levels 2, 5
56Fe Iron :
number of electron by energy levels 2, 8, 14, 2
156Rh Rhodium :
number of electron by energy levels 2, 8, 18, 16, 1
173Pt Platinium :
number of electron by energy levels 2, 8, 18, 32, 17, 1
177
O  Oxygen :
number of electron by energy levels 2, 6
48Co Cobalt :
number of electron by energy levels 2, 8, 15, 2
152Pd Palladium :
number of electron by energy levels 2, 8, 18, 18
169Au Gold :
number of electron by energy levels 2, 8, 18, 32, 18, 1
174
F  Fluorine :
number of electron by energy levels 2, 7
42Ni Nickel :
number of electron by energy levels 2, 8, 16, 2 or 2, 8, 17, 1
149Ag Silver :
number of electron by energy levels 2, 8, 18, 18, 1
165Hg Mercury :
number of electron by energy levels 2, 8, 18, 32, 18, 2
171
Ne Neon :
number of electron by energy levels 2, 8
38Cu Copper :
number of electron by energy levels 2, 8, 18, 1
145Cd Cadmium :
number of electron by energy levels 2, 8, 18, 18, 2
161TL Thallium :
number of electron by energy levels 2, 8, 18, 32, 18, 3
156
Na Sodium :
number of electron by energy levels 2, 8, 1
190Zn Zinc :
number of electron by energy levels 2, 8, 18, 2
142In Indium :
number of electron by energy levels 2, 8, 18, 18, 3
156Pb Lead :
number of electron by energy levels 2, 8, 18, 32, 18, 4
154
Mg Magnesium :
number of electron by energy levels 2, 8, 2
145Ga Gallium :
number of electron by energy levels 2, 8, 18, 3
136Sn Tin :
number of electron by energy levels 2, 8, 18, 18, 4
145Bi Bismuth :
number of electron by energy levels 2, 8, 18, 32, 18, 5
143
Al Aluminium :
number of electron by energy levels 2, 8, 3
118Ge Germanium :
number of electron by energy levels 2, 8, 18, 4
125Sb Antimony :
number of electron by energy levels 2, 8, 18, 18, 5
133Po Polonium :
number of electron by energy levels 2, 8, 18, 32, 18, 6
135
Si Silicon :
number of electron by energy levels 2, 8, 4
111As Arsenic :
number of electron by energy levels 2, 8, 18, 5
114Te Tellurium :
number of electron by energy levels 2, 8, 18, 18, 6
123At Astatine :
number of electron by energy levels 2, 8, 18, 32, 18, 7
127
P  Phosphorus :
number of electron by energy levels 2, 8, 5
98Se Selenium :
number of electron by energy levels 2, 8, 18, 6
103I  Iodine :
number of electron by energy levels 2, 8, 18, 18, 7
115Rn Radon :
number of electron by energy levels 2, 8, 18, 32, 18, 8
120
S  Sulfur :
number of electron by energy levels 2, 8, 6
88Br Bromine :
number of electron by energy levels 2, 8, 18, 7
94Xe Xenon :
number of electron by energy levels 2, 8, 18, 18, 8
108  
Cl Clorine :
number of electron by energy levels 2, 8, 7
79Kr Krypton :
number of electron by energy levels 2, 8, 18, 8
88Cs Caesium :
number of electron by energy levels 2, 8, 18, 18, 8, 1
298  
Ar Argon :
number of electron by energy levels 2, 8, 8
71Rb Rubidium :
number of electron by energy levels 2, 8, 18, 8, 1
265Ba Barium :
number of electron by energy levels 2, 8, 18, 18, 8, 2
253  
K  Potassium :
number of electron by energy levels 2, 8, 8, 1
243Sr Strontium :
number of electron by energy levels 2, 8, 18, 8, 2
219Lu Lutetium :
number of electron by energy levels 2, 8, 18, 32, 9, 2
217  

Table: Theoretical Atomic radius (calculated) of certain atoms, the size is given in picometers (10-12 meters). The atomic radius is half the distance between the nuclei of two adjacent atoms. The values ​​in this table are only indicative.

Size of atoms

Image: Since the 1990's through tunneling microscope it is possible to view and manipulate individual atoms on the surface of a material. This allows for small atomic structures that are the basis of nanotechnology.
To make this type of image, the very fine tip of scanning tunneling microscope scans the surface of the material, a few nanometers of altitude by emitting a constant voltage. Passing over the atomic orbitals, it is able to record tiny variations of the tunnel current which will flow to the surface.
On the surface of the material, a small flow of electrons able to cross the potential barrier by "tunnel effect", a well-known phenomenon of quantum mechanics. This electric current is measured by the scanning tunneling microscope, and the tip faithfully reproduces the surface topography with a resolution on the order of 0.1 nanometer or one angstrom, that is, the size of the atom. Thus we can see today, the mysterious quantum world in which evolve all particles of matter, and visualize the crystal structure of chemical elements in the infinitely small. Credit image: STM Image Gallery Blue Nickel.

NB: Several atoms can form chemical connections among themselves through their electrons and in general terms, the chemical properties of atoms are determined by their electronic configuration, which derives from the number of protons in their nuclei. This number, called the atomic number, defines a chemical element.

The smallest film in the world

Since the 1990's through tunneling microscope it is possible to see and manipulate individual atoms on the surface of a material.
This film was made by IBM, with iron atoms on a copper plate, this is the smallest movie in the world.
In this nano movie each light is an atom, which occupies 12 pixels on this screen. Small waves that create oscillations around bright points are not a fault of the film but the electron waves. These Friedel oscillations are not an oddity but betray the quantum nature of atoms, both particles and waves. The shape of these oscillations of electrons constitute a real ID.
This film at the nanometer scale, measuring 52 by 32 iron atoms, i.e. ≈8 nanometers on ≈5 nanometers. On a length of 1 mm we could align 10 000 films of this size.
Each image is produced with the tip of a scanning tunneling microscope, a few degrees of absolute zero, this is also the coldest film in the world.

NB: Jacques Friedel (1921 - 2014) was a French physicist, professor emeritus at the University Paris-Sud Orsay, specialist in theoretical solid state physics. He was president of the Academy of Sciences for the period 1993-1994.


The smallest film in the world
On a length of 1 mm we could align 10 000 films of this size.

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