IT IS ELEMENTARY
Human Existence and the Chemical
Elements
SC 210
May 28, 2015
John Bush
“The Periodic Table ranks as one of the most
fruitful and unifying ideas in the whole of
modern science, comparable perhaps with
Darwin’s theory of evolution by natural
selection”
Eric R. Scerri The Periodic Table: Its Story
and Its Significance Oxford University
Press, 2007
STEPS LEADING TO A PERIODIC TABLE
1. Identify substances that meet the criteria
established for elements
2. Determine their properties
3. Find regularities among these properties
4. Arrange the elements in such a way that
elements with common features are associated
with one another
ELEMENTS: WHAT CRITERIA?
• A substance that cannot be decomposed into
simpler substances by ordinary chemical
processes
• A pure chemical substance consisting of a
single kind of atom distinguished by its atomic
number
DISCOVERY OF THE CHEMICAL ELEMENTS
• Antiquity to 1669: 13 elements
• 1669-1799: 21 elements
• 1800-1849: 24 elements
• 1850-1899: 26 elements
……………………………………………………………………
• 1900-1949: 13 elements
• 1950-1999: 16 elements
• 2000-2015: 5 elements
ELEMENTS: WHAT PROPERTIES?
• Physical properties: melting/boiling point;
electrical/thermal conductivity; color; odor;
specific heat; density; emission/absorption
spectra; refractive index; hardness; ductility,
malleability; ionization energy; atomic radius;
crystal structure; atomic weight; atomic
number
• Chemical properties: reactivity of elements;
reactivity of compounds; valences;
electronegativity; oxidation numbers; toxicity;
solubility
ELEMENTS: WHAT KIND OF
REGULARITIES?
• Ordering by atomic weight
• Ordering by atomic number
• Ordering by filling of atomic orbitals
“THE PERIODIC TABLE”
PERIODIC TABLES OF THE ELEMENTS
A MODERNIZED “CLASSIC” VERSION
NATIONAL INSTITUTES OF STANDARDS AND
TECHNOLOGY
PHYSICISTS PREFER THIS ONE
GEOLOGISTS PREFER THIS ONE
KARLSRUHE CONFERENCE 1860
• Convened to straighten out the confusion
about atomic weights
• Is the atomic weight of oxygen 8 or 16?
• Is the formula for water HO or H2O?
• Avogadro/Cannizarro- the hydrogen molecule
and the oxygen molecule are diatomic
• Therefore the correct atomic weight of oxygen
is 16!
DE CHANCOURTOIS
1862
LOTHAR MEYER 1860-70
MENDELEEV’S PERIODIC TABLE-1869
MENDELEEV’S PREDICTIONS
Property
•atomic mass
•density (g/cm3)
•melting point (°C)
•oxide's formula
•chloride's formula
Ekaaluminum
68
6.0
Low
Ea2O3*
Ea2Cl6 (volatile)
Gallium
69.72
5.904
29.78
Ga2O3 **
Ga2Cl6 (volatile)
*(density: 5.5 g/cm3) (amphoteric-soluble in both alkalis and acids)
**(density: 5.88 g/cm3) (amphoteric-soluble in both alkalis and acids)
MENDELEEV’S PREDICTIONS
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Property
Ekasilicon
atomic mass
72
density (g/cm3)
5.5
melting point (°C)
high
color
grey
oxide type
EO2 (refractory)
oxide density (g/cm3)
4.7
oxide activity
feebly basic
chloride b.p.
under 100 °C
chloride density (g/cm3)
1.9
Germanium
72.61
5.35
947
grey
GeO2(refractory)
4.7
feebly basic
86 °C (GeCl4)
1.9
SOME IMPORTANT MILESTONES
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X-rays –Roentgen 1895
Radioactivity –Becquerel 1896
Electron –J J Thomson 1897
Nuclear atom –Rutherford 1911
Isotopes --Soddy 1913
Planetary model of the atom –Bohr 1913
Atomic number -Moseley 1914
Proton – Rutherford 1917
HENRY MOSELEY
DMITRI MENDELEEV
SOME MORE DISCOVERY MILESTONES
• Wave mechanics model of the atom-1930s
• Valence Bond Theory-Heitler/London/Pauling
1930
• Molecular Orbital Theory -Hund/Mulliken
1932
• Neutron-Chadwick 1932
• Actinides-Seaborg 1944
• Nuclear shell model-Wigner, Goeppert-Meyer,
Jensen 1949
GLENN T SEABORG
SEABORG-MODIFIED PERIODIC TABLE
SOME MORE DISCOVERY MILESTONES
• Wave mechanics model of the atom-1930s
• Valence Bond Theory-Heitler/London/Pauling
1930
• Molecular Orbital Theory -Hund/Mulliken
1932
• Neutron-Chadwick 1932
• Actinides-Seaborg 1944
• Nuclear shell model-Wigner, Goeppert-Meyer,
Jensen 1949
ATOMIC ORBITALS
HYDROGEN ATOMIC ORBITALS
ATOMIC ORBITALS AND THE PERIODIC TABLEELECTRON MAGIC NUMBERS
• Fill the lowest energy empty orbital first
• Organize orbitals in shells: 1(s) 6(p) 10(d) 14(f)
• Fill each available orbital with maximum of 2 electrons
Atomic number
Element
[1s ]
n=2
He
[1s][2s2p]
[1s][2s2p][3s3p]
[Ar][4s3d4p]
[Kr][5s4d5p]
[Xe] [6s4f5d6p]
[Rn] [7s5f6d7p]
n=10
n=18
n=36
n=54
n=86
n=118
Ne
Ar
Kr
Xe
Rn
Uuo
FILLING ATOMIC ORBITALS
NATURALLY OCCURRING RADIOACTIVE
ELEMENTS
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Potassium
Thorium
Uranium
Radon
Actinium
Radium
Polonium
Astatine
(Plutonium)
RADIOACTIVE DECAY CHAINS
• Sequences of nuclear transformations ending
in the formation of stable isotopes
• Examples
– 232ThRa, Ac, Bi. Po, Tl, 208 Pb
– 238U Th, Pa, Ra, Rn, Po, At, Bi, Hg, 206 Pb
– 235U Th, Pa, Ac, Fr, At, Rn, Bi, Tl, 207Pb
ELEMENTS ARISING FROM DECAY OR
SYNTHESIS
• Produced by radioactive decay: 14
Technetium, Polonium, Astatine, Radon, Francium,
Radium, Actinium, Protoactinium, Neptunium,
Americium, Curium, Berkelium, Californium
• Produced by synthesis: 21
Plutonium, Einsteinium, Fermium, Mendeleevium,
Nobelium, Lawrencium, Rutherfordium, Dubnium,
Seaborgium, Bohrium, Hassium, Meitnerium,
Darmstadtium, Roentgenium, Copernicium, 113,
Flerovium, 115, Livermorium, 117, 118
HOW MANY ELEMENTS CAN THE
PERIODIC TABLE CONTAIN?
• Is there any limit to the number of atomic
orbitals?
• Is there any limit to the magnitude of atomic
numbers?
DO YOU BELIEVE IN MAGIC (NUMBERS)?
HALFLIVES OF MOST STABLE ISOTOPES
ISLANDS OF STABILITY?
• Based on shell model of the nucleus
• Nuclei with filled shells of protons and
neutrons (“magic numbers”) have extra
stability
• Synthetic nuclei with magic numbers may be
long lived (islands of stability}
TWO PROBLEMS
• What are the correct magic numbers?
• How can you make the elements?
DO PERIODIC TABLES OF CHEMICAL
ELEMENTS HAVE A FUTURE?
• Yes Z<79
• Maybe Z>80
• No Z>120