CLASSIFICATION OF ELEMENTS

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COMPUTER CAREERS

Periodic Table“It is defined as the table in which all the elements are arranged in the order of increasing atomic numbers.”

In other words, it classifies all the known elements according to their properties so that the elements with similar properties are placed together in same group while with different properties are separated from each other.

1. To study the elements in a better way

2. To correlate the properties of the elements.

3. To study relationship between different elements.

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NEED OF CLASSIFICATION

Four main groups:1. Main group elements - elements

having outer shells consisting solely of s and p electrons (s and p block elements)

2. Transition metals – first, second and third transition series. ( d block)

3. Lanthanides – 4f orbitals being filled4. Actinides – 5f orbitals being filled

Lanthanides and Actinides = f block elements

The Periodic Table – Classification of Elements

Classification of ElementsThe main group elements (also called the representative elements) are the elements in Groups 1A through 7A.

Classification of ElementsThe noble gases are found in Group 8A and have completely filled p subshells.

The Modern Periodic TableThe transition metals are found in Group 1B and 3B through 8B.Group 2B have filled d subshells and are not transition metals.

The Modern Periodic TableThe lanthanides and actinides make up the f-block transition elements.

The Modern Periodic TableThere is a distinct pattern to the electron configurations of the elements in a particular group.

For Group 1A: [noble gas]ns1 For Group 2A: [noble gas]ns2

BLOcKS A block of the periodic table of elements is a set of adjacent groups. The respective highest-energy electrons in each element in a block belong to the same atomic orbital type. Each block is named after its characteristic orbital. thus, the blocks are:s-blockp-blockd-blockf-blockg-block (hypothetical)

LET US UNDERSTAND ABOUT EACH BLOCK - -

S BLOCKThe S-block is a block in the periodic table that consists of the first two groups.The elements in the s-block generally exhibit well-defined trends in their physical and chemical properties, changing steadily moving down the groups.Their properties can be most readily explained in terms of their electron configuration, with their valence electrons occupying s-orbitals.

P BLOCK

P BlockThe p-block of the periodic table of the elements consists of the last six groups except helium (which is located in the s-block).In the elemental form of the p-block elements, the highest energy electron occupies a p-orbital.The p-block contains all of the nonmetals (except for hydrogen and helium, which are in the s-block) and semimetals, as well as the post-transition metals.The groups of the p-block are: (IIIB, IIIA): Boron group14 (IVB, IVA): Carbon group15 (VB, VA): Nitrogen group (or pnictogens)16 (VIB, VIA): Chalcogens17 (VIIB, VIIA): Halogens18 (Group 0): Noble gases (excluding helium)

D BLOCKThe d-block is the block or portion of the periodic table that contains the element groups 3–12.These groups correspond to the filling of the atomic d-orbital sub shell of the second outermost shell with electron configurations ranging from s2d1 (Group 3) to s2d10 (Group 12).The d-block elements are often also known as transition metals or transition elementsHowever the exact limits of the transition metal region are usually not considered to be identical to the d-block.There are some irregularities in the sequence; for example Cr is s1d5 (not s2d4) and the Group 11 metals are s1d10(not s2d9), so that the d-subshell is actually complete at Group 11.

F BLOCKThe f-block of the periodic table of the elements consists of those elements whose atoms or ions have valence electrons in f-orbitals.Actual electronic configurations may be slightly different from what is predicted by the Aufbau principle.The elements are also known as inner transition elements, although that term is normally taken to include lutetium and lawrencium as well, which are part of the d-block.

G BlockThere are currently seven periods in the periodic table of chemical elements, culminating with atomic number 118.If further elements with higher atomic numbers than this are discovered, they will be placed in additional periods, laid out to illustrate periodically recurring trends in the properties of the elements concerned.No elements in this region have been synthesized or discovered in nature.The first element of the g-block may have atomic number121, and thus would have the systematic name unbiunium.Elements in this region are likely to be highly unstable with respect to radioactive decay, and have extremely short half lives, although element 126 is hypothesized to be within an island of stability that is resistant to fission but not to alpha decay.According to the orbital approximation in quantum mechanical descriptions of atomic structure, the g-block would correspond to elements with partially filled g-orbitals. However, spin-orbit coupling effects reduce the validity of the orbital approximation substantially for elements of high atomic number.

INERT GASES Inert gases are gases that belong to Group VIII at the periodic table and its distinct characteristic is that they will hardly react and even do not react at all with other chemical such as metal or acid. These undesirable chemical reactions are often oxidation and hydrolysis reactions with the oxygen and moisture in air.Purified nitrogen and argon gases are most commonly used as inert gases due to their high natural abundance (78% N2, 1% Ar in air) and low relative cost.Inert gas is produced on board crude oil carriers (above 20,000 tonnes) by using either a flue gas system or by burning kerosene in a dedicated inert gas generator.The costs of inert gases are directly related to how difficult it is to extract them from the air.

NOW LET US KNOW INERT GASES IN DETAIL : -

Name  Symbol  Atomic     Boiling      Max. Avail.      Amt. in  the                  Number    Point(C)   Pressure (PSI)     Atmosphere     US$/ltr.

Helium    He       2      -268.9         6,000            5.2 PPM     $  .10

Neon       Ne      10       -246.07        6,000           18.2 PPM      $ 1.00  

Argon      Ar     18       -185.88        6,000         7600 PPM        $  .10   Krypton   Kr      36      -156.6          1,350           1.1 PPM        $ 3.00

Xenon     Xe     54      -108.06          800          0.036 PPM     $11.00

INERT GASES

REPRESENTATIVE OR MAIN GROUP ELEMENTS

What are representative elements in the periodic table?The representative elements are all the elements in groups one, two, thirteen, fourteen, fifteen, sixteen, seventeen and eighteen of the periodic table.The representative elements in the periodic table do not exhibit variable valencies.

These include metals, non metals and semi metals (metalloid). 

The metals are present in the left groups of the representative elements, while the non metals are present in the right most groups and the semi metals (metalloid) are present in the middle in a the shape of a zig zag line that separates the metals from the non metals. 

These elements are also called the main group elements of the periodic table. 

There are a total of 44 elements in representative elements.

These include the Alkali metals, the Alkaline earth metals, theHalogens, the Nitrogen family, the Carbon family of elements, the Oxygen family of elements, the Boron family of elements and the noble gases present at the far right group.

The main group elements form the S and P blocks of the periodic table.

These elements are the most abundant elements on the earth.

ATOMIC ORBITALS

An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom.

Atomic orbitals are the basic building blocks of the atomic orbital model, a modern framework for visualizing the submicroscopic behavior of electrons in matter.

In this model the electron cloud of a multi-electron atom may be seen as being built up in an electron configuration that is a product of simpler hydrogen-like atomic orbitals.

The repeating periodicity of the blocks of 2, 6, 10, and 14 elements within sections of the periodic table arises naturally from the total number of electrons which occupy a complete set of s, p, d and f atomic orbitals, respectively.

SHAPES OF ORBITALS

The atomic orbitals differ in shape.

That is, the electrons they describe have different probability distributions around the nucleus.

Indeed, a part of the reason why orbitals differ in energy is that the electrons that occupy them are likely to be found in different regions around the parent nucleus and hence experience the latter's attraction with different strengths.

The fact that all orbitals of a given shell in the hydrogen atom have the same energy despite having different shapes is surprising and is associated with a cancellation of different contributions to the energy.

The possession of the same energy by different wavefunctions, is also associated with the coincidental numerical agreement of Bohr's model with experiment

Let us know about about Orbitals : -

S Orbitals

All s orbitals are spherically symmetrical. That is, an electron that occupies an s orbital can be found with the same probability at any orientation from the nucleus. 2 S When an electron is described by the wavefunction corresponding to a particular orbital, the electron is said to occupy that orbital.

When an electron is described by the wavefunction corresponding to a particular orbital, the electron is said to occupy that orbital.

All other orbitals have zero amplitude at the nucleus, and an electron that occupies one of them has zero probability of being found there.

It is largely responsible, for instance, for the structure of the periodic table and hence for the pattern of the compounds that the elements can form and for the properties of the substances that make up the tangible world.

S ORBITALS

P ORBITALSAll p orbitals have adumbbell shape.The Second kind of label are subscripts which distinguish between orbitals which are basically the same shape but differ in their orientation in space. In the case of p orbitals there are always three orientations possible.A p orbital which extends along the x axis is labeled a px orbital and A p orbital along the y axis is labeled pyand one along the z axis is a pz orbital.When n equals 3, three orbital types occur.so the 3s and 3p orbitals differ slightly in shape from the 2s and 2p orbitals.

P ORBITALS

2Px and 2Py

2Pz

D ORBITALSThe d orbitals have more complex shapes than the p orbitals.

In the case of the dorbitals the subscripts are more difficult to follow.

You can puzzle them out from the rotating images, the dot density diagrams and the orbital surface diagrams if you like, but analysis of these orbitals is usually considered beyond the scope of general chemistry.

The same pattern extends to n = 4 where four orbital types, namely, 4s, 4p, 4dand 4f, are found.

While none of these orbitals will be shown, the patterns seen in moving from 1s to 2s or from 2p to 3p continue with the s, p, and d orbitals

D ORBITALS

D ORBITALS

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