classification of elements
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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.
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