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CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES of elements

CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES of elements. BY- A.P.S. BHADOURIYA M.Sc. , B.Ed., NET PGT-CHEMISTRY K.V. BARABANKI. Session Objectives. Why do we need classification .? Dobereniner’s triads Newlands law of octave Lother Meyer volume curve

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CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES of elements

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  1. CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES of elements BY- A.P.S. BHADOURIYA M.Sc. , B.Ed., NET PGT-CHEMISTRY K.V. BARABANKI

  2. SessionObjectives • Why do we need classification.? • Dobereniner’s triads • Newlands law of octave • Lother Meyer volume curve • Mendeleev’s periodic table • Modern periodic table • IUPAC nomenculature for elements Z >100 • 8. Periodic Trends in Physical Properties • Shielding effect & Effective Nuclear Charge • Atomic Radius • Ionic Radius • Ionization Enthalpy • Electron Gain Enthalpy • Electronegativity • 9. Periodic Trends in Chemical Properties • Periodicity of Valence or Oxidation States • Anomalous Properties of Second Period Elements • Chemical Reactivity

  3. During the nineteenth century, chemists began to categorize the elements according to similarities in their physical and chemical properties. The end result of these studies was our modern periodic table. Lavoisier (1789) classified elements into metals, non-metals, gases and earths.

  4. Arithmetic mean of atomic masses of first and third element Atomic masses of elements of triad S.No Triad 35.5 + 127 = 81.25 1 Cl,Br,I 35.5, 80, 127 2 40+137 Ca,Sr,Ba 3 40,87.5,137 = 88.5 2 Dobereiner’s triads [ John Dobereiner (1817)] In 1829, he classified some elements into groups of three, which he called triads.The elements in a triad had similar chemical properties and orderly physical properties. 2 Li,Na,K 7, 23, 39 7 + 39 = 23 2 Model of triads

  5. Newland’s law of octaves [John Newland (1866)] In 1866, he suggested that elements be arranged in “octaves” because he noticed (after arranging the elements in order of increasing atomic mass) that certain properties repeated every 8th element.

  6. Newland’s law of octaves [John Newland (1863)] Newland was first to publish the list of elements in increasing order of atomic masses.

  7. Lother-Meyer’s atomic volume curve [Lother Meyer (1869)]

  8. Dmitri Mendeleev 1834 - 1907 In 1869 he published a table of the elements organized by increasing atomic mass.

  9. Mendeleev’s periodic law The physical and chemical properties of elements are periodic function of their atomic masses.

  10. Mendeleev’s periodic table

  11. Mendeleev’s periodic table Only 63 elements were known. Groups • 8 vertical rows. • 7 groups were subdivided in A and B. • 8th group has 9 elements in the group of 3 each. Periods • 7 horizontal rows.

  12. Prediction of new elements (Ge, Ga, Sc) 1 Systematic study of elements Correction of atomic mass (Be, Au, Pt) 2 3 Merits of Mendeleev’s periodic table

  13. Mendeleev • stated that if the atomic weight of an element caused it to be placed in the wrong group, then the weight must be wrong. (He corrected the atomic masses of Be, In, and U) • was so confident in his table that he used it to predict the physical properties of three elements that were yet unknown. After the discovery of these unknown elements between 1874 and 1885, and the fact that Mendeleev’s predictions for Sc, Ga, and Ge were amazingly close to the actual values, his table was generally accepted.

  14. Position of hydrogen. Defects of Mendeleev’s periodic table Position of isotopes e.g. 1H1, 1H2, 1H3 Anomalous pairs.(Ar and K, Co and Ni, Te and I)

  15. Defects of Mendeleev’s periodic table Chemically dissimilar elements are grouped together. (Cu-IA and Na-IB) Chemically similar elements are placed in different groups. [Cu (I) and Hg (II)].

  16. Do you know? Mendeleev’s periodic table was published in 1905 when no one had an idea of the structure of an atom. Mendeleev’s name has been immortalized by naming the element with atomic number 101, as Mendelevium. This name was proposed by American scientist Glenn T. Seaborg, the discoverer of this element, “in recognition of the pioneering role of the great Russian Chemist who was the first to use the periodic system of elements to predict the chemical properties of undiscovered elements, a principle which has been the key to the discovery of nearly all the transuranium elements

  17. MODERN PERIODIC LAW AND THE MODERN PERIODIC TABLE English physicist, Henry Moseley observed regularities in the characteristic X-ray spectra. A plot of fagainst atomic number (Z ) of the elements gave a straight line and not the plot of fvs atomic mass He thereby showed that the atomic number is a more fundamental property of an element than its atomic mass.

  18. Mendeleev’s Periodic Law was, therefore, accordingly modified. This is known as the Modern Periodic Law and can be stated as : The physical and chemical properties of the elements are periodic functions of their atomic numbers.

  19. Henry Moseley In 1913, through his work with X-rays, he determined the actual nuclear charge (atomic number) of the elements*. He rearranged the elements in order of increasing atomic number. *“There is in the atom a fundamental quantity which increases by regular steps as we pass from each element to the next. This quantity can only be the charge on the central positive nucleus.” His research was halted when the British government sent him to serve as a foot soldier in WWI. He was killed in the fighting in Gallipoli by a sniper’s bullet, at the age of 28. Because of this loss, the British government later restricted its scientists to noncombatant duties during WWII.

  20. Modern periodic table

  21. Features of long form of periodic table • Contains elements arranged in increasing order of atomic numbers. • Explains the position of an element in relation to other elements. • Consists of groups and periods.

  22. Features of long form of periodic table Groups Vertical column Total 18. Numbered 1-18 orIA to VII A, IB to VII B, VIII and zero. Elements in a group have similar but notidentical electronic configuration and properties Horizontal column Periods Total 7 numbered from 1 to 7. Contains 2,8,8,18,18,32 and 28 elements respectively.

  23. ELECTRONIC CONFIGURATIONS AND TYPES OF ELEMENTS: s-,p-,d-,f- Block Elements On the basis of the nature of sub-shell in which last electron of atom enters, elements are divided into 4 blocks • s-Block Element • p-Block Element • d-Block Element • f- Block Element

  24. s-Block Elements In these elements last electron enters the s-orbital • Electronic configuration: ns1 or ns2 IA (alkali metals )and IIA(alkaline earth metals • Groups: • All are metal, low ionisation energy and low melting and boiling points, electropositive elements. • compounds are mostly ionic & colourless.

  25. p-Block Elements In these elements last electron enters the p-orbital • Electronic configuration: ns2,np1 -6 • Groups: III A to VII A and zero group (group 13-18). • Non-metals, electronegative. • Form covalent compounds.

  26. d-Block Elements In these elements last electron enters the d-orbital, Also known as transition metals. • Electronic configuration: (n-1)d1-10 ns1or2 • Groups: I B to VII B and VIII groups (Gr- 3-12). • Variable valency high melting and boiling point. • Coloured compounds and catalytic property.

  27. f-Block Elements In these elements last electron enters the f-orbital, Also known as Inner-Transition Elements • Electronic configuration: (n-2)f1-14(n-1)d0-1ns2 • Present below the periodic table in two rows • Lanthanides-elements afterlanthanum(Gr.-3, Pd.-6) • Actinides-elements after actinium. (Gr.-3, Pd.-7) • Have high melting and boiling point.

  28. Features of long form of periodic table Representative elements s and p block elements . Transition elements d-block elements. Valence shell and penultimate Shell both are incomplete. Inner Transition elements f-block elements. Valence shell, penultimate shellantipenultimate shell are incomplete.

  29. Features of long form of periodic table Metals • Present on left hand side of periodic table. • Solid,malleable,ductile and conductors . Non-metals • Present on right hand side of periodic table. • Solid or liquid or gas. Metalloids • Present on zig-zag between metals and non-metals. e.g. B,Si,Ge,As,Sb and Te.

  30. Merits of long form of periodic table • Based on a more fundamental basis - the atomic number • Position of an element is related to the electronic configuration of its atom. • Due to separation of elements into groups, dissimilar elements (e.g. alkali metals I A and coinage metals I B) do not fall together.

  31. Defects of long form of periodic table It is unable to include lanthanides and actinides in its main body. The problem of the position of hydrogen in the table has not been solved completely Configuration of Helium(1s2 ) is different from inert gases (ns2,np6) but are placed in the same group.

  32. Nomenclature of the elementswith atomic number >100 Name =digits name + ium e.g. atomic number 115 Will be named as un+un+pent+ium =ununpentium and symbol is Uup

  33. Periodic Properties • Periodic Trends in Physical Properties • Shielding effect & Effective Nuclear Charge • Atomic Radius • Ionic Radius • Ionization Enthalpy • Electron Gain Enthalpy • Electronegativity

  34. Periodic Properties • Periodic Trends in Chemical Properties • Periodicity of Valence or Oxidation States • Anomalous Properties of Second Period Elements • Chemical Reactivity

  35. Shielding effect & Effective Nuclear Charge The decrease in nuclear charge ( nuclear force of attraction) on outermost shell electrons due to repulsion caused by inner shell electron is known as shielding effectof inner shell or intervening electrons on outer shell electron.

  36. Shielding effect & Effective Nuclear Charge Due to shielding effect the nuclear charge is lowered on outermost shell electrons, the net nuclear charge acting on outermost shell electrons is known as Effective Nuclear Charge. It is denoted by Z* or Zeff. • Z* or Zeff. = Z - σ • where Z = nuclear charge( = atomic No.) & • σ = shielding constant or screening constant , it is a measure of shielding effect

  37. Shielding effect & Effective Nuclear Charge Determination of ENC (Z*) If the electron resides in s or p orbital 1. Electrons in principal shell higher than the e- in question contribute 0 to σ . 2. Each electron in the same principal shell contribute 0.35 to σ (0.30 if it is 1S shell). 3. Electrons in (n-1) shell each contribute 0.85 to σ . 4. Eelectrons in deeper shell each contribute 1.00 to σ

  38. Shielding effect & Effective Nuclear Charge Determination of ENC (Z*) If the electron resides in d or f orbital 1. All e-s in higher principal shell contribute 0 to σ 2. Each e- in same shell contribute 0.35 to σ 3. All inner shells in (n-1) and lower contribute 1.00 to σ

  39. Shielding effect & Effective Nuclear Charge Determination of ENC (Z*) e.g.Calculate the Z* for the 2p electronFluorine (Z = 9) 1s2, 2s 2p5. Soln.Screening constant for one of the outer electron • 6 (six) (two 2s e- and four 2p e-) = 6 X 0.35 = 2.10 • 2 (two)1s e- = 2 X 0.85 = 1.70 • σ = 1.70+2.10 = 3.80 • Z* = 9 - 3.80 = 5.20

  40. Shielding effect & Effective Nuclear Charge Trend of ENC in Periodic Table • In a Period - Effective nuclear charge Z* increases increases rapidly along a period(0.65 per next group) e.g.

  41. Shielding effect & Effective Nuclear Charge Trend of ENC in Periodic Table • In a Group - Effective nuclear charge Z* increases slowly along a group. e.g.

  42. PERIODIC TREND OF ATOMIC RADIUS In A Period- • atomic radius decreases with increasein atomic number (in a period left to right) BECAUSE in a period left to right- • 1. n (number of shells) remain constant. • 2. Z increases (by one unit) • 3. Z* increases (by 0.65 unit) • 4. Electrons are pulled close to the nucleus by the increased Z*

  43. In a group- Atomic radius increases moving down the group • Because, along a group top to bottom 1. n increases 2. Z increases 3. No dramatic increase in Z* - almost remains constant

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