Contents
1 Characteristics
2.Properties
of the electron
3. History of
discovery
4.Mendeleev
5.Structure
of the periodic system
6.Groups
7.Periods
8.Blocks
9.Other
periodic patterns
10.Literature
Atom (from the
Greek atomos - indivisible) - mononuclear, chemically indivisible particle of a
chemical element, the carrier material properties. Substances consist of atoms.
The atom itself consists of a positively charged nucleus and the negatively
charged electron cloud. In general, the atom is electrically neutral. Size of
the atom is completely determined by the size of its electron cloud, since the
size of the nucleus is negligible compared to the size of the electron cloud.
The core consists of positively charged protons Z (proton charge corresponds to
1 in arbitrary units) and N neutrons, which do not carry a charge (protons and
neutrons are called nucleons). Thus the nuclear charge determined only by the
number of protons and atomic number is equal to the periodic table. Positive
charge of the nucleus is compensated by negatively charged electrons (electron
charge -1 in arbitrary units) that form the electron cloud. Thus the number of
electrons equal to the number of protons. The mass of protons and neutrons are
(respectively 1 and 1 amu). Determine the mass of the atomic mass of its
nucleus, because the electron mass is about 1850 times smaller than the mass of
the proton and neutron, and rarely taken into account in the calculations. The
number of neutrons can be found from the difference between the mass of the
atom number of protons (N = AZ). Kind of atoms of a chemical element with a
nucleus consisting of a well-defined number of protons (Z) and neutrons (N) is
called a nuclide
Since
the nucleus of an atom is concentrated almost all mass, but its size is
negligible compared with the total volume of the atom, the nucleus is
conventionally assumed a material point at rest in the center of the atom, and
the atom is regarded as a system of electrons. Chemical reaction nucleus of an
atom is not affected (except nuclear reactions) as the internal electronic
levels, and involves only the outer electron shell electrons. For this reason
it is necessary to know the properties of the electron and the rules for the
formation of the electron shells.
Properties of the
electron
Before
examining the properties of the electron and the rules of formation of the
electronic levels, it is necessary to address the history of the formation of
ideas about the structure of the atom. We will not consider the complete
history of the formation of atomic structure, and focus only on the most urgent
and the most "faithful" representations that can most clearly show
how electrons are arranged in an atom. The first presence of atoms as
elementary constituents of matter, suggested another ancient Greek
philosophers. After that, the story structure of the atom was a difficult path
and different ideas, such as the indivisibility of the atom, the Thomson model
of the atom, and others. The closest model of the atom was proposed by Ernest
Rutherford in 1911. He compared the atom to the solar system where the sun
acted as an atom's nucleus and electrons moving around him like planets.
Placing electrons in fixed orbits was a very important step in the
understanding of atomic structure. However, such a planetary model of the atom
was in contradiction with classical mechanics. The fact that the motion of an
electron in orbit he had to lose potential energy and eventually "fall"
into the nucleus and the atom was to cease to exist. This paradox was
eliminated by the introduction of Niels Bohr postulates. According to these
postulates an electron moving on stationary orbits around the nucleus under
normal conditions is not absorbed and emitted energy. Postulates show that to
describe the atom laws of classical mechanics do not fit. This model is called
the Bohr model of the atom, Rutherford. Continuation of the planetary structure
of the atom is a quantum-mechanical model of the atom, according to which we
shall consider an electron.
Electron
is showing quasiparticle wave-particle duality. He is both a particle
(corpuscle) and a wave. By properties include particle mass of the electron and
its charge, and to the wave properties - the ability for the diffraction and
interference. Communication between the wave and particle properties of the
electron is reflected in the de Broglie equation:
where - wavelength -
mass of the particle -
particle -
Planck's constant = 6,63 • 10-34 J • s.
For
an electron can not calculate its trajectory, we can only talk about the
probability of finding an electron in a particular place around the nucleus.
For this reason, do not speak about the orbits of the electron around the
nucleus, and on the orbitals - the space around the nucleus in which the
probability of finding an electron is greater than 95%. For an electron is
impossible to accurately measure both the position and velocity (Heisenberg
uncertainty principle). The more precisely we
measure the electron coordinate, the greater the error in the measurement of
its velocity, and vice versa: the more precisely we know the electron velocity,
the greater the uncertainty in its coordinate. The
presence of the wave properties of the electron allows us to apply it to the
Schrödinger wave equation.
where
- the total electron energy, potential
energy, the physical meaning of the function - the square root of the probability of finding an
electron in a space with coordinates x, y and z (the kernel is considered the
origin).
Represented
by the equation written for the one-electron system. For systems with more than
one electron description principle remains the same, but the equation takes a
more complicated form. Graphic solution of the Schrödinger equation is the
geometry of the atomic orbitals. Since s-orbital is spherical, p-orbital - a
figure eight "knot" at the origin (at the nucleus), where the
probability of finding an electron tends to zero.
In
the framework of modern quantum mechanical theory of the electron is described
by a set of quantum numbers: n, l, ml, s and ms. According to the Pauli
principle in one atom can not be two electrons with completely identical set of
quantum numbers.
Principal
quantum number n determines the energy level of the electron, that is what the
electronic level is given electron. The principal quantum number can take only
integer values greater than 0: n = 1, 2, 3 ... n The maximum value for a
particular atom of an element corresponds to the period in which the item is
located in the periodic table of Mendeleev.
Electrons in the
levels and orbitals are not placed randomly but according to the rule
Klechkovskii whereby electrons are filling on the principle of minimum energy,
ie in order of increasing amounts of principal and orbital quantum numbers n +
l. In case the programming code for the two variants of filling the same,
originally filled lowest energy level (for example, when n = 3 and l = 2 and n
= 4 and l = 1 is initially filled will be level 3). The magnetic quantum number
ml determines the location of the orbitals in space, and can be an integer
value from-l to + l including 0. For the s-orbitals is only one value of ml =
0. For p-orbitals for three values -1, 0 and 1, that is p-orbital can be
placed in three axes x, y and z.
Electron
has intrinsic angular momentum - spin quantum number is denoted s. Electron
spin - constant and equal to 1/2. The phenomenon of spin can be conventionally
represented as a movement around its own axis. Initially, the electron spin
equated to the movement of the planet around its own axis, but such a
comparison is misleading. Spin - a purely quantum phenomenon, which has no
analogues in classical mechanics.
Periodic
Table of Elements ( Mendeleev's table ) - classification of chemical elements ,
which establishes the dependence of various properties of the elements of the
charge of the atomic nucleus. The system is a graphic expression of the
periodic law , established by the Russian chemist Mendeleev in 1869. Its
original version was developed by Mendeleev in the 1869-1871 years , and
established the dependence of properties of elements to their atomic weight (in
the modern , from the atomic mass ) . Total proposed several hundred [1 ] the
image of the periodic system options ( analytical curves , tables, geometric
shapes , etc.) . In the modern version of the system is assumed mixing elements
in the two-dimensional table in which each column (group ) defines the basic
physical and chemical properties , and the rows represent periods to a certain
extent similar to each other.
History
of discovery
By
the middle of the XIX century were discovered 63 chemical elements , and try to
find patterns in this set have been made repeatedly . In 1829 Dobereiner
published found them "law triads " : atomic weight of many elements
close to the arithmetic mean of the other two elements close to the original
chemical properties (strontium , calcium and barium , chlorine, bromine and
iodine , etc.). The first attempt to arrange elements in order of increasing
atomic weights taken Chancourtois Emil Alexander (1862 ), which placed the
elements along the helix and noted frequent cyclic repetition of chemical
properties of vertically. Both of these models do not attract the attention of
the scientific community.
In 1866, his
version of the periodic system proposed chemist and musician John Alexander
Newlands , the model of which ( the "law of octaves ") looks a bit
like Mendeleev , but was compromised by persistent attempts to find a table 's
mystical musical harmony . In the same decade, appeared a few attempts to
systematize chemical elements closest to the final version came Julius Lothar
Meyer (1864 ) . Mendeleev published his periodic table of the first scheme in
1869 in the article " Value of properties with an atomic weight of
elements" ( in the Journal of the Russian Chemical Society ) , even before
( February 1869 ) a notice of scientific discovery was sent to them the world
's leading chemists . The opening day of the periodic law is considered to
March 1 ( February 17 , Old Style ), 1869 , which Mendeleev finished work on
"experience of the elements, based on their atomic weight and chemical
similarity .
Mendeleev
According to
legend , the idea of chemical elements came to Mendeleev in a dream , but we
know that once the question of how he discovered the periodic system , the scientist
said, " I'm working on it, maybe twenty years of thought , and you think,
and suddenly sat ready ... ".
Writing on
cards the basic properties of each element ( them while 63 were known , one of
which - Didim Di - helpful in further mixture of two newly discovered elements
praseodymium and neodymium ) , begins Mendeleev repeatedly rearrange these
cards , make one series of similar properties elements match series with one
another . The work was sent in 1869 in the scientific institutions of Russia
and other countries, the first version of the system ( "Experience system
elements based on their atomic weight and chemical similarity "), in which
the elements were arranged by nineteen horizontal rows ( rows of similar items,
which became the prototype groups of modern systems) and six vertical columns (
the prototype for future periods). In 1870 Mendeleev " Fundamentals of
Chemistry " published the second version of the system (" The natural
system of elements "), having a more familiar to us form horizontal
columns elements peers turned into eight groups of vertically arranged , six
vertical columns of the first version turned into periods beginning alkaline
metal and ending with halogen. Each period was divided into two rows of
different elements included in a group of rows formed subgroups.
The essence
of Mendeleev's discovery was the fact that with increasing atomic mass of
chemical elements their properties do not change monotonically , and
periodically . After a certain number of different properties of the elements
in order of increasing atomic weight , the properties begin to repeat . For
example , similar to potassium , sodium , similar to fluoro chloro and the like
gold silver and copper. Naturally , the properties do not repeat exactly added
thereto and changes. Honors the work of Mendeleev's work of his predecessors
was that the basis for classification of the elements Mendeleev was not one,
but two - the atomic mass and chemical similarity . In order to fully comply
with the periodicity , Mendeleev had taken very bold steps he corrected the
atomic masses of some elements (eg , beryllium, indium , uranium, thorium ,
cerium , titanium, yttrium ) , multiple items posted in their system , contrary
to accepted while representations about their similarity to others (eg ,
thallium , which was considered an alkali metal, he placed third in the group
according to its actual maximum valence) , leave empty cells in a table , where
they were to stay until the open elements . In 1871, on the basis of these
studies formulated Mendeleev 's periodic law , the form of which eventually was
somewhat improved.
Scientific
credibility of the periodic law was confirmed very soon : in the years
1875-1886 were discovered gallium ( ekaalyuminy ) , scandium ( ekabor ) and
germanium ( ekasilitsy ) for which Mendeleev , using a periodic system ,
predicted not only the possibility of their existence , but also with amazing
accuracy , described a number of physical and chemical properties.
At the beginning of XX century with the discovery of the structure of atoms ,
it was found that the frequency of changes in the properties of elements is not
determined by atomic weight and nuclear charge equal to the atomic number and
the number of electrons , which are distributed as electron shells of atoms of
element determines its chemical properties.Further development of the periodic
system involves filling empty cells of the table , which were placed in more
and more new elements: noble gases , natural and artificially produced
radioactive elements . In 2010 , with the synthesis of element 117 , the
seventh period of the periodic system was completed , the problem of the lower
boundary of the periodic table is one of the most important in modern
theoretical chemistry.
Structure of
the periodic system
The most
common are three forms of the periodic table : "short" ( short-period
) , "long" ( long-period ) and " Extra long ." In "
Ultra Long " version of each period takes exactly one line . In the
"long" version of the lanthanides and actinides are removed from the
common table , making it more compact . In the "short" form of the
recording , in addition to this , the fourth and subsequent periods occupied by
two lines , characters and the main elements of sub-group aligned with the
edges of the various cells.The short form of the table , with eight groups of
elements , was officially abolished by IUPAC in 1989. Despite the
recommendation to use the long form , short form continues to be driven in a
large number of Russian handbooks and manuals , and after this time. Of modern
foreign literature , short form is completely excluded , used instead the long
form . Such a situation , some researchers have linked including apparent
rational compactness of the short form of the table , as well as inertia,
stereotyped thinking and modern non-perception (international) information.
In 1970,
Theodore Seaborg proposed extended periodic table of elements . Niels Bohr
developed staircase ( pyramidal ) shape of the periodic system . There are many
others , rarely or not used , but highly original , graphical way to display
the Periodic Law . Today, there are hundreds of options table, the scientists
propose new variants .
Groups
Group or
family , - one of the columns of the periodic table. For groups tend to have
significantly more pronounced periodic trends than to the frames or blocks.
Modern quantum mechanical theories of atomic structure explain group
commonality that elements within the same group usually have the same electron
configurations in their valence shells . Accordingly , the elements that belong
to the same group traditionally have similar chemical characteristics , and
exhibit a clear pattern of change in properties with increasing atomic number .
However, in some fields of the table , for example - in the d- block and f-
block horizontal similarity may be just as important or even more markedly
pronounced than vertical .
In accordance
with the international system of naming groups are numbered from 1 to 18 from
left to right - from the alkali metals to the noble gases . Previously used to
identify them Roman numerals . In American practice after Roman numerals also
posed letter A ( if the group is located in the s- block or p- block ) or B ( if
the group was in the d- block) . Then applied identifiers correspond to the
last digit of modern numerical indicators - for example, elements of the group
4 corresponds to the name of IVB, but to those who are now known as a group of
14 - IVA. A similar system has been used in Europe, except that the letter
A refers to the group prior to the tenth , and B - to the groups after the
tenth inclusive. Groups 8, 9 and 10 , moreover, is often regarded as one triple
group identifier VIII. In 1988 came into effect new IUPAC notation system , and
former names of groups out of use.
Some of these
groups have been assigned the trivial , non-systematic name (such as "
alkaline metals ", " halogen ", etc. ), but some of them are
rarely used. Groups three through fourteenth inclusive, do not have the same
names and their identified either by number or by name representative of the
first (" titanium ", " cobalt " and so forth ), since they
exhibit a lesser degree of similarity between a vertical line or minimal laws ]
.
Elements
belonging to the same group tend to show certain trends in atomic radius,
ionization energy and electronegativity . From top to bottom within a group the
atomic radius increases ( the more he filled energy levels , the farther from
the nucleus are arranged valence electrons ), and the ionization energy
decreases ( due to weaker atom , and therefore it becomes easier to remove an
electron ) , as well as and electronegativity (which, in turn, caused an
increase in the distance between the valence electrons and the nucleus ) .
Happen , however, are exceptions to these laws - for example, in a group of 11
from top to bottom electronegativity increases and does not decrease .
Periods
Period - row of
the periodic table . Although groups , as mentioned above , is characterized by
more significant trends and patterns , there are also areas where the
horizontal direction is more significant and indicative rather than vertical -
eg regarding f- block , where the lanthanides and actinides form two important
horizontal sequence of elements
Within the period
of the elements exhibit a definite pattern in the three aspects mentioned above
( the atomic radius and electronegativity of the ionization energy ) , and in
electron affinity . From left to right the atomic radius usually decreases (
due to the fact that each subsequent element increases the number of charged
particles and electrons are drawn closer to the nucleus and parallel with
increasing ionization energy (the stronger bond in the atom , the more energy
is required to withdraw electron). increases accordingly and
elektrootritsatelnostChto regard the electron affinity , the metal on the left
side of the table are characterized by a lower value of this index , and
non-metals on the right , respectively , great - except for the noble gases
Blocks
In
view of the importance of the outer electron shell of the atom different areas
of the periodic table are sometimes described as units called in accordance
with those on which the shell is the last electron. S- block includes the first
two groups , that is, alkali and alkaline earth metals , as well as hydrogen
and helium ; p- block consists of the last six groups ( 13 to 18 according to
standard IUPAC naming , or IIIA to VIIIA by American system ), and includes
among other elements , all of metalloids . D- block - this group of 3 to 12 (
IUPAC ) , they - with stage IIIB to IIB -American , which includes
vseperehodnye metals . F- block vynosimy typically beyond the table consists of
lanthanides and actinides
Other
periodic patterns
Electronic
configuration . Organization electrons demonstrates certain periodic repeating
pattern. Electrons occupy a sequence of shells which are identified by numbers
(sheath 1 , the sheath 2, etc. ) , and those in turn are composed of sub-levels
defined letters s, p, d, f and g. Increasing atomic number of electrons
gradually fill these shells , and each time the electron takes a new shell for
the first time , a new period in the table. Similarities in the electron configuration
determine the similarity properties of the elements ( watching them , in fact,
led to otkrytiyuperiodicheskogo law).
Metallicity
/ nemetallichnost . The lowering of the ionization energy indicators ,
electronegativity and electron affinity elements acquire features typical of
metals, and as they increase - on the contrary, for non-metals ] . In
accordance with the laws for the aforementioned characteristics , the most
pronounced metals are located at the beginning of the period, and non-metals -
at its end. In groups , in contrast, as one moves from top to bottom metal
properties are intensified , albeit with some exceptions to the general rule .
The combination of horizontal and vertical patterns gives conditional dividing
line between metals and nonmetals stepped form , along this line elements are
sometimes defined as metalloids .
Value
of the periodic system
Periodic
system of Mendeleev was a milestone in the development of the atomic- molecular
theory . Thanks to her, had the modern concept of the chemical elements have
been refined notions of simple substances and compounds.
The predictive
role of the periodic system , shown by another Mendeleev in the XX century was
manifested in the evaluation of chemical properties of transuranic elements .
Developed in the
XIX century . within the science of chemistry , the periodic table was finished
ordering of types of atoms for new areas of physics , which have developed in
the early XX century. - Atomic physics and nuclear physics . Studies atom
physics methods , it was found that the serial number of the element in the
periodic table (atomic number ) is a measure of the electric charge of the
atomic core of this element , the horizontal row number ( period) in the table
determines the number of electron shells of atoms , and the number of vertical
rows - quantum structure upper shell , what elements of the series and
similarity of chemical properties are required .
The appearance of
the periodic system has opened a new , genuinely scientific era in the history
of chemistry and related sciences series - instead of disparate information
about the elements and compounds appeared orderly system on which it became
possible to generalize, draw conclusions , predict.
Literature
D.I
Mendeleev - periodic law of chemical elements / / Encyclopedic Dictionary Brockhaus
and Efron : In 86 volumes ( 82 tons and 4 extra. ) . - St. Petersburg. ,
1890-1907 .
Agafoshina NP
periodic law and the periodic system of elements Mendeleev . - M.: Education ,
1973 . - 208 .
Evdokimov Yu ,
Ph.D. Chem . Sciences . On the history of the periodic law . Science and Life ,
№ 5 (2009), pp. 12-15 .
Makarenya AA Rysev
YV Mendeleev . - M.: Education , 1983 . - 128 p.
Makarenya AA
Trifonov DN periodic law of Mendeleev . - M.: Education , 1969 . - 160 .
Eric R. Scerri.
The Periodic Table: Its Story and Its Significance. - New York : Oxford
University Press, 2007 . - 368 .
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