After this lecture you will be able to :

• Understand the significance of classification.• Know about the history of development of periodic

table.• Understand the modern periodic law & present

form of periodic table.• Learn the various periodic trends in properties of

elements.

• Rapid development during the 18th and 19th century including the discovery of several new elements.

• This gave rise to need of classification of elements into groups with similar properties.

• Thus, classification of elements resulted in the formulation of periodic table.

• Father of the Periodic Table• Periodic Law- Both physical and

chemical properties of the elements vary periodically with increasing atomic mass.

• Exception placed Te (M = 127.6) a head of I (M=126.9) because Te was similar to Se and S, and I was similar to Cl and Br.

• Left gaps in periodic table and predicted new elements would be found. Predicted the new elements’ properties.

Utility of Mendeleev’s Periodic Table

• Systematic study of elements• Prediction of new elements• Correction of atomic masses• Use in research

Defects of Mendeleev’s Periodic Table

• Position of Hydrogen and isotopes• Separation of similar elements• Heavier elements placed before lighter ones• Improper arranging of Lanthanides and Actinides

• Meyer (1870)-Arranged elements according to their physical properties.

• Elements changed properties gradually in a row or period.• Moseley (1930)- Arrange atoms according to atomic

number (nuclear charge). He found a direct correlation between the square root of X-ray energy and nuclear charge (atomic number). Nuclear charge increases by one unit for each element.

•The way the periodic table usually seen is The way the periodic table usually seen is a compress view, placing the Lanthanides a compress view, placing the Lanthanides and actinides at the bottom of the stable.and actinides at the bottom of the stable.•The Periodic Table can be arrange by sub The Periodic Table can be arrange by sub shells. The s-block is Group IA and & IIA, shells. The s-block is Group IA and & IIA, the p-block is Group IIIA - VIIIA. The d-the p-block is Group IIIA - VIIIA. The d-block is the transition metals, and the f-block is the transition metals, and the f-block are the Lanthanides and Actinide block are the Lanthanides and Actinide metalsmetals

•B•2p1

1IA

18VIIIA

12IIA

13IIIA

14IVA

15VA

16VIA

17VIIA

2

33

IIIB4IVB

5VB

6VIB

7VIIB

8 9VIIIB

10 11IB

12IIB

4

5

6

7

H1s1

Li2s1

Na3s1

K4s1

Rb5s1

Cs6s1

Fr7s1

Be2s2

Mg3s2

Ca4s2

Sr5s2

Ba6s2

Ra7s2

Sc3d1

Ti3d2

V3d3

Cr4s13d5

Mn3d5

Fe3d6

Co3d7

Ni3d8

Zn3d10

Cu4s13d10

B2p1

C2p2

N2p3

O2p4

F2p5

Ne2p6

He1s2

Al3p1

Ga4p1

In5p1

Tl6p1

Si3p2

Ge4p2

Sn5p2

Pb6p2

P3p3

As4p3

Sb5p3

Bi6p3

S3p4

Se4p4

Te5p4

Po6p4

Cl3p5

Be4p5

I5p5

At6p5

Ar3p6

Kr4p6

Xe5p6

Rn6p6

Y4d1

La5d1

Ac6d1

Cd4d10

Hg5d10

Ag5s14d10

Au6s15d10

Zr4d2

Hf5d2

Rf6d2

Nb4d3

Ta5d3

Db6d3

Mo5s14d5

W6s15d5

Sg7s16d5

Tc4d5

Re5d5

Bh6d5

Ru4d6

Os5d6

Hs6d6

Rh4d7

Ir5d7

Mt6d7

Ni4d8

Ni5d8

•Various Elemental Properties change fairly smoothly going across a period or down a group

•Properties include:–Atomic and Ionic Radius–Ionization Enthalpy–Electron gain Enthalpy–Electronegativity–Valency

•Atomic Radius: Atomic Radius:

•The size of at atomic specie as determine by the boundaries of the valence e-. Largest atomic species are those found in the SW corner since these atoms have the largest n, but the smallest Zeff.

• Cations are always smaller than the original atom.

• The entire outer PEL is removed during ionization.

• Conversely, anions are always larger than the original atom.

• Electrons are added to the outer PEL.

11p+

Na atom

1 valence electron

Valence e- lost in ion formation

Effective nuclear charge on remaining electrons increases.

Remaining e- are pulled in closer to the nucleus. Ionic size decreases.

Result: a smaller sodium cation, Na+

17p+

Chlorine atom with 7 valence e-

One e- is added to the outer shell.

Effective nuclear charge is reduced and the e- cloud expands.

A chloride ion is produced. It is larger than the original atom.

Ionization enthalpy: Ionization enthalpy:

The energy required to remove the valence electron from an atomic specie. Largest toward NE corner of PT since these atoms hold on to their valence e- the tightest.

Electron Affinity: Electron Affinity:

The energy release when an electron is added to an atom. Most favorable toward NE corner of PT since these atoms have a great affinity for e-.

• Electronegativity is a measure of an atom’s attraction for another atom’s electrons.

• It is an arbitrary scale that ranges from 0 to 4.• The units of electronegativity are Paulings.• Generally, metals are electron givers and have low

electronegativities.• Nonmetals are are electron takers and have high

electronegativities.