Periodic table discussed about Chemicals. These are mainly two types: those elements and compounds. Among the 88 known elements in the elemental form and about 26 are of human origin. It is difficult to individually analyze the chemistry of more than a hundred elements hitherto known, and numerous compounds. Experimental data elements and compounds can be systematized classification only if it is done properly. The basic purpose of classification is to arrange the facts of elements and their compounds, so that we can have more control over their properties with the least effort possible. Classification would be the best collection of elements that are similar in many respects and is separated from the others.
Genesis of periodic classification
After the proposal of John Dalton´s atomic theory, the scientists took atomic weight as the important property of elements and tried to seek relationship between the properties of the elements and their atomic weights.
John Dobereiner pointed out that there were sets of three elements which showed similar chemical properties. Such sets are named as triads. The atomic weight of the middle element of a triads was approximately the average of the atomic weights of the other two members. Examples of triads are: Li, Na and K; Ca Sr and Ba; Cl, Br and I; etc.
John Newland arranged the elements in increasing order of their atomic weights and found that some elements as the eighth element that followed. The proportion was the same between a note and its octave. This development has been called the law of octaves. The system worked well for the lighter elements. For example, H, F and Cl show similar properties.
Lother Meyer presented the classification in the form of a curve. Lother Meyer calculated the atomic volumes of known elements as the ratio of molecular weight and density.
Mendeleef’s periodic law
Mendeleeff relied on the similarities in the empirical formulae and properties of compounds by the elements. Mendeleeff put forward the periodic law, stated as
“The physical and chemical properties of the elements and their compounds are a periodic function of their atomic weight”.
In Mendeleeff’s periodic table elements are arranged in the increasing order of their atomic weights.
In the periodic table, elements are arranged in vertical columns called groups and horizontal rows called periods. Each group is divided into two subgroups "A" and "B". The first three periods are called short periods and the remaining are called long periods. Each long period contains two rows of elements called series.
While arranging the elements in the periodic table, he followed the increasing order of atomic weights and also considered their properties. If the properties of elements did not correspond to what is expected for that place, he left blank places and proposed the properties of elements to be present in blanks.
Mosley is bombarded by different elements, that does so much with cathode rays of anticathode on the drain hose. This has led to an x-ray with a characteristic frequency. Mosley has demonstrated that high frequency ka and KB line x-ray due to the charge on the atomic nucleus used element anticathode.
√ v = a(Z-b)
Here v is the frequency of X-rays, 'Z' is the atomic number, 'a' and 'b' are constants for 'a' selected type of line. A plot of Root 'v' against ‘Z’ gives a straight line as shown in fig.1. No such relationship was obtained using mass number. According to Moseley, atomic number stands for a serial number. As atomic number increases in regular steps. Thus properties of an element are dictated by its electrons. This led to the proposal of modern periodic law.
Modern Periodic law
Empirical development of the periodic classification of the peak in 1913, when Moseley showed that the atomic number of an element as a fundamental property of its atomic weight. The position of an element in the periodic table depends on the atomic number and the reason for the anomaly of the original periodic table immediately clear. Periodic table of Mendeleev Mosley changed as specified.
“The physical and chemical properties of the elements are periodic function of their atomic numbers”.
Atomic number is nuclear charge, or the number of elements in the neutral atom. In addition, it was felt that the periodic law is essentially the result of periodic oscillations in the electronic configuration. Configuration properties and really define their connections and is the basis for the modern periodic law. Modern periodic law States that the physical and chemical properties of elements are periodic functions of their atomic numbers or their electron configuration.
The original form of the periodic table have been modified to clarify the structure of the atom and the discovery of the noble gases. Worked a long time in the form of periodic table, from time to time. Mosley was the periodic table, the periodic, where elements are arranged according to atomic number. This is very similar to Bohr' thomson table.
The most convenient version of the periodic table was constructed by Bhor based on the modern periodic law and arranged the elements in the order of their electronic configurations.
The modern version of the form advanced and widely used in the periodic table shown above. It has the same number of horizontal lines, which is a series of Mendeleeff table. This horizontal rows called periods. External items similar configuration of electron in atoms in vertical columns are arranged. These columns of hot groups or families. A day are now 18 groups and 7 periods.
Long Form of periodic table
The long form of the periodic table is based on the electronic configuration if the elements. The elements are arranged in the increasing order of atomic numbers. “The long form of periodic table is a graphical representation of auf-bau principle”.
In the periodic table that has the horizontal line hot periods, and the principal quantum number, assigned to the outer orbit of the atom. There are seven periods. Each period begins with the alkali metals and finishing with an inert gas. In each period the differences between the orbits of electrons in p orbitals in the last element of the first object. Sub-Energy filled in every period of the periodic table in table Sub - energy are displayed. and the number of elements present in each period in Table- Number of elements present in different periods.
|Sub - energy levels filled in periods||Number of elements present in different periods|
Nomenclature of elements
The name of new parts have traditionally had the honour, the discoverer (or researchers) and suggested that the IUPAC ratified the name. In recent years, this has led to controversy. New products with a large number of Atomic is so volatile that only one minute, sometimes only a few atoms get quantities of this. Their synthesis and their properties and does so very complex and costly equipment and laboratory. This work is done with fighting spirit only in a few laboratories in the world. Scientists obtain, collect reliable data on the new coins are sometimes tempted to open them argue.
For example, to detect Soviet and American scientists claim a 104. The Americans had the name Rutherfordium and name-Kurchatovium Soviet troops. To avoid these problems, it is recommended that the IUPAC officially recognized before the opening of the new evidence, and his name is nomenclature for atomic number element with a digital 0 and numbers from 1 to 9. As shown in table IUPAC notation. Roots, from the point of the atomic number, and "manual" be added at the end. Table IUPAC Nomenclatuer IUPAC for elements with more than 100 names and Z.
|IUPAC notation for naming elements with Z >100||IUPAC Nomenclatuer for heavy elements|
Thus, the new element is a temporary name, the symbol, which consists of three letters first. Later, by the representatives of the IUPAC in each country is a permanent name and symbol in a survey. Permanent name may reflect the country (or countries) who discovered the element or numbers was tribute to an eminent scientific. You already have elements of atomic number 112, 114 and 116 points with ordinals, 113, 115, 117 and 118 are still unknown.
The vertical columns of the periodic table hot groups or families. There are 18 groups. Among this group, eight are important. These groups are: 1, 2, 13, 14, 15, 16, 17 and 18. Part appears the Group 3-split element at the bottom of the periodic table in the form of lanthanides and actinides. Fourteen elements that come after the lanthanum called lanthanides. Lanthanides are CERIUM (Z = 58) to Lutetium (Z = 71). Fourteen elements following Actinium called actinides. Actinide is thorium (Z = 90), Lawrencium (Z = 103). Lanthanides are referred to often rare earths. The majority of the actinides are mainly synthetic elements.
Hydrogen is the only element, which can be placed in two different groups of the periodic table: group 1 and group 17.
Electronic configuration in periods
A critical remark suggests the long form of the periodic table, as follows:
- the number of elements in each period is twice the number of orbital atomic power level which is filled.
- The serial number is the number of the shell in the distance from the nucleus of an atom, electrons present.
- In each period of the periodic table is that multiple parties main filled energy level.
The first period starts with filling of lowest energy level, 1s(K shell). The period has two elements. Hydrogen has the electronic configuration 1s1 and helium has 1s2.
The second period starts with lithium. The differentiating electron of lithium enters the 2s(L shell) and has the electronic configuration 1s2 2s1. The 2p orbital are filled starting from boran. The second shell is completely filled at neon (2s2 2p6). Thuse there are eight elements in the second period.
The third period starts with sodium with differentiating electron enters the 3s orbital (M shell) Successive filling of 3s and 3p sub - shell gives rise to third period of eight element from sodium to argon.
The fourth period start at potassium (2,8,8,1) with filling up of 4s (N shell). Filling of 4s is complete with calcium. Before the 4p orbitals, filling up of 3d orbitals (M shell ) becomes energetically favourable. Ten elements from scandium to Zinc are filled with differentiating electrons in 3d sub - shell. The period ends with krypton with the filling up of the 4p orbitals. Thus there are eighteen elements in the fourth period. In this period exceptionally Cr and Cu has one electron in the outershell, i.e., 4s orbital
The fifth period begins with Rubidium filling up of 5s orbital. Similar to that in fourth period, 4d sub - shell is filled starting at yttrium and up to
Cadmium. The period ends at Xenon with the filling up of the 5p orbitals. Thus the fifth period also has eighteen elements.
The sixth period starts with Caesium. The period has thirty two elements and electrons are filled successively in 6s, 4f, 5d and 6p orbitals. Filling up of the 4f orbitals begins with cerium and ends at lutetium to give 4f series, also called lanthanide series. There are thirty two elements in the sixth period ( longest period ).
The seventh period starts with Francium. This period is incomplete and is expected to end at the elements with atomic number 118. Filling up of the 5f orbital after Actinium gives 5f series, also called Actinide series.
While the typical hydrogen is separately shown above the periodic table, the elements of 4f and 5f series are also placed separately. This is to maintain the structure and preserve the principle of classification by keeping elements with similar properties in a single column.
Electronic configuration in groups
The main reason for the classification is to group together elements which are chemically similar. Elements present in the same group have similar electronic configuration and have same number of electrons in the outermost shells.
The elements of group 1 or alkali metals have only one electron in outermost shell of each atom. The general electronic configuration of alkali metals is ns1. The elements of group 2 or alkaline earth metals have two electrons in the outermost shell of each atom. The general electronic configuration of alkaline earth metal is ns2. The group number in Roman symbol for representative elements directly denotes the number of electrons present in the outermost shell of atom of each element. Atoms of the elements of group III A (or group 13) have three electrons in the outermost shell. Their general electronic configuration is ns2np1. Similarly group IVA (or group 14) elements have general configuration ns2np4, etc. Noble gas elements (group 18), however, have filled octet in their outermost shells with GroupWise general electronic configuration of the important groups are listed in below Table -Configuration of first and last element of each period . Nickel group has an exceptional feature. This group is called pseudo-octet configuration group. The element palladium has the electronic configuration 1s2 2s2 2p63s23p64s23d104p64d10, with eighteen elements of the same group have similar outer shell electronic configuration, though there are few anomalies.
Configuration of first and last element of each period
|Period||First group element||Electronic configuration||Last group element||Electronic Configuration|
Classification of Elements.
Many attempts were made to classify elements according to one property or the other. Elements were classified into solids, liquids and gases based on the physical states. Elements were also classified into metals and non-metals. They were classified according to their valency as monovalent, divalent, trivalent, etc. All these early classifications were considered as rough classifications. The best way to classify elements is based on their electronic configuration.
Classification into blocks
Based on the entry of the differentiating electro into the sub-shells, elements are classified into four blocks. They are:
- S-block elements
- P-block elements
- D-block elements and
- F-block elements
Different blocks of the elements in the long form of the periodic table are given in the picture. S-block is present at the left side, p-block is at the right, d-block is at the middle and f-block at the bottom of the long form of the periodic table. Atomic number of aluminum is 13. The thirteenth electron of aluminium enters into 3p- orbital. Hence aluminium is called p-block element. Similary atomic number of titaninum is 22, with the configuration of the differentiating electron 3d2. Titanium is called a d-block element. He due to 1s2 configuration belongs to ‘s’ block, but placed in zero group due to its inert nature.
S – Block elements.
The elements in which the differentiating electro enters the s-orbital of the outermost shell are called s-block elements. The first two elements of each period belong to the s-block. Group 1 and 2 (alkali and alkaline earth metals) constitute the s-block. These elements are located at the left side of the long form of the periodic table. The general electronic configuration of s-block elements is ns1-2. Characteristic properties of S-block elements of s-block elements are:
- The elements are highly electropositive and are soft metals with lower densities.
- They are very good reducing agents.
- They have low melting and boiling points.
- They are very reactive and form ionic substances, except Lithium and Beryllium.
- They exhibit and oxidation state of +1 or +2.
- They impart characteristic colours in the flame.
The elements in which the differentiating electron enters the p-orbitals of the outermost shell are called p-block elements. Groups 13, 14, 15, 16, 17, and 18 (IIIA to VIIA and Zero groups) constitute the p-block. Group 18 element that is misplaced in p-block is helium. These elements are located at the right side of the periodic table. The p block elements together with s block elements (except zero group) are referred to as representative elements or main group elements. The general electronic configuration of p-block elements in ns2 np2 np1-6 or ns2 npx (x=1 to6). Characteristic properties of p-block elements are :
- The elements include all metalloids, most of the non-metals and some metals.
- All gaseous elements (except H2 and He) are p-block elements.
- Most of these elements are highly electronegative and have high electron gain enthalpy.
- Some elements are good oxidizing agents. Some of them act as reducing agents.
- Except group 18, these elements are very reactive.
- They form mostly covalent compounds eg:Cl2,O2, HCl) though ionic halides, oxides, sulphides, nitrides, etc., are also known.
The elements in which the differentiating electron enters the d-orbitals of the penultimate shell are called d-block elements. Groups 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 constitute the d-block. These elements are located at the middle, in between s-block and p-block of the long form of the periodic table. They have the properties intermediate to those of the s-block and p-block elements. They are referred to as transition elements. The d-block contains four series of elements. The d-block contains four series of elements. The 3d-, 4d- and 5d- series are completely filled with ten elements each. The 6d- series is incomplete and has onbly eight elements. Zinc, cadmium and mercury, which have the electronic configuration (n-1)d10ns2, do not show most of the properties of transition elements. The general electronic configuration of d-block elements is (n-1)d1-10ns1or ns2. Characteristic properties of d-block elements are :
- The elements are all electropositive and are metals.
- They are all solids, except mercury which is al liquid at room temperature.
- Most of the elements possess catalytic activity
eg : In the preparation of NH3 by Haber’s process, Catalyst is platinised asbestos.
eg : In the preparation of H2SO4 by Contact process, catalyst is platinised asbestos.
- They form cations with different magnitude of the charge.
- They form ionic as well as covalent compounds.
- They form complex compounds,
Eg : [Cu(NH3)4]SO4, K4[Fe(CN)6]
- They form alloys and interstitial compounds.
- They mostly form coloured ions, exhibit variable valency (eg : Fe+2, Fe+3) and paramagnetism. (µ = 4.90 BM for Fe+2, µ=5.92 BM for Fe+3)
The elements in which the differentiating electron enters the f-orbitals of the antepenultimate hell are called f-block elements. A part of group 3 constitutes the f-block. These elements are located at the bottom of the periodic table. There are two series of f-block elements. The first series follows lanthanum (Z=57) and are called lanthanides [Ce(Z=58) to Lu(Z=71)]. The second series follows actinium (Z=89) and are called actinides [Th(Z=90) to Lr (Z=103)]. The general electronic configuration of f-block elements is (n-2)f1-14(n-1)d0or1 ns2.La and Ac are d-block elements but lanthanides and actinides are f-block elements. Characteristic properties of f-block elements:
- These elements are heavy metals with high density and form coloured ions, complexes and show paramagnetic property, similar to d-block elements.
- They are naturally available in very small quantities and are called rare earths.
- Trans-uranic elements (Z > 92) are all synthetic.
- They also form complexes and interstitial compounds.
- They show a great deal of similarity among themselves in their properties.
- Actinide elements are radioactive.
- Actinides show more number of oxidation states compared to lanthanides.
Classification into types
All elements are classified into four types considering their properties based on the configuration in different shells of the elements.
- Type I elements are called inert gases.
- Type II elements are called representative elements.
- Type III elements are called transition elements and
- Type IV elements are called inner transition elements.
The difference in the electronic configuration of different shells of these four types of elements determines their chemical behavior.
Inert gas elements.
Elements in which the outermost s and p subshells completely filled are called inert gas elements. Elements of group 18 constitute this type. The elements are He, Ne, Ar, Kr, Xe and Rn. All these elements are gases and due to inertness these are monoatomic. The general electronic configuration of inert gas elements is ns2 np6 (configuration of helium is 1s2). Presence of eight electrons in the outermost shell is called octet configuration. The significance of octet is that it explains the stability. Due to their low reactivity, elements of group 18 are called inert gases. The first compound of xenon was reported with fluorine in 1982. There after, these elements are called noble gases. The natural availability of these elements is very less and are also called rare gases.
Elements in which the outermost s and p subshells(nth shell) are incompletely filled are called representative elements. Elements of groups 1, 2, 13, 14, 15, 16 and 17 (all ‘A’ groups) constitute this type. All the s- and p- block elements except group 18 are known as representative elements. They are also called normal elements. The general electronic configuration of these elements is ns1-2 np0-5. These elements undergo chemical reactions to acquire the nearest inert gas configuration either by losing or gaining or by sharing electrons, and some of them may even get pseudo intert gas configuration. These elements are so named because theyrepresent most of the chemical reactions known. The most reactive element is fluorine. Many non-metals, metalloids and some metals are present in this type of elements.
Elements in which the ultimate and penultimate shells (n and (n-1) shells) are partially filled are called transition elements. These elements are so named as they represent properties intermediate between most electropositive s-block elements and most electronegative p-block elements. They are the d-block elements. All the transition elements are metals and solids. The general electronic configuration of transition elements is (n-1)d1-10 ns1or2. They possess incompletely filled (n-1)d orbitals in their higher oxidation states. The elements of group 12 (Zn, Cd and Hg) are not included in the transition elements as they have completely filled penultimate shell in both atomic and ionic states. The elements of group 11 (Cu, Ag and Au) also have completely filled penultimate shell. They are called typical transition elements as some of their ions resemble the transition elements.
The transition elements exhibit characteristic properties due to 1) the partially filled d-orbitals in the penultimate shell, 20 small atomic size and 30 high nuclear charge. Some special properties of the transition elements are:
- Transition elements exhibit variable oxidation states, eg : Fe+2 , Fe+3
- They form coloured compounds and coloured ions in solution due to d-d transition of electrons by absorbing the visible light.
- They are paramagnetic. Iron, cobalt and nickel are ferromagnetic.
- They possess catalytic activity. Nickel is used as catalyst in the hydrogenation of oils and iron in Haber’s ammonia synthesis. Molybdenum acts as promoter in Haber’s process.
- They form alloys ( ex : Brass, Bronze German silver) and interstitial compounds. Hydrogen is occluded on palladium.
- They form complex compounds and alloys.
- Common oxidation state of transition elements is +2.
- They have high melting point, boiling point and densities.
Inner transition elements
Elements in which the ultimate, penultimate and antepenultimate shells (n,(n-1) and (n-2) shells) are partially filled are called inner transition elements. These elements are so named as they represent a transition of physical and chemical properties among transition elements. They are the f-block elements. There are two series of inner transition elements namely Lanthanides and actinides corresponding to the 4f and 5f series. All the inner transition elements are metals. The general electronic configuration of inner transition elements is (n-2)f1-14 (n-1)d0or1ns2. The elements in each series of inner transition elements closely resemble in their properties. Hence, their isolation and separation by the usual methods is very difficult. For the sake of convenience, the inner transition elements are placed as separate f-block below the main body of the long form of the periodic table. Inner transition elements are all heavy metals. Their natural availability is either rare or not at all available. Actinides are synthetic except Th and U. They exhibit variable oxidation states and magnetism. They are also known to form complex compounds. Common oxidation state of inner transition elements in +3.