An Overview of the Periodic Table

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Chapter 2

• An Overview of the Periodic Table

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History of the Periodic Table

• Johann Döbereiner (1780-1849)
• in 1817, organized elements into triads

Examples of Döbereiners Triads Examples of Döbereiners Triads Examples of Döbereiners Triads Examples of Döbereiners Triads
First Element Third Element Second Element Triad 1 Triad 2 Triad 3
First Element Third Element Second Element Name/Mass Calcium/40.1 Barium/137.3 Average 88.7 Strontium/87.6 Name/Mass Chlorine/35.5 Iodine/126.9 Average 81.2 Bromine/80.0 Name/Mass Sulfur/32.1 Tellurium/127.6 Average 79.9 Selenium/79.0
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History of the Periodic Table

• John Newlands (1837-1898)
• in 1863, postulated the law of octaves

Examples of Newlands Octaves Examples of Newlands Octaves Examples of Newlands Octaves Examples of Newlands Octaves Examples of Newlands Octaves Examples of Newlands Octaves Examples of Newlands Octaves
H Li Ga B C N O
F Na Mg Al Si P S
Cl K Ca Cr Ti Mn Fe
Co,Ni Cu Zn Y In As Se
Br Rb Sr Ce,La Zr Di,Mo Ro,Ru
Pd Ag Cd U Sn Sb Te
I Cs Ba,V Ta W Nb Au
Pt,Ir Tl Pb Th Hg Bi Cs
Adapted from Isaac Asimovs, A Short History of Chemistry. Adapted from Isaac Asimovs, A Short History of Chemistry. Adapted from Isaac Asimovs, A Short History of Chemistry. Adapted from Isaac Asimovs, A Short History of Chemistry. Adapted from Isaac Asimovs, A Short History of Chemistry. Adapted from Isaac Asimovs, A Short History of Chemistry. Adapted from Isaac Asimovs, A Short History of Chemistry.
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History of the Periodic Table

• Dmitri Mendeleev (1834-1907)
• in 1872, organized the elements in eight columns
  in order of increasing atomic mass
• left spaces to fit the similar properties of
  certain elements
• unknown elements properties could be predicted
  based upon its neighbors

Element Atomic Weight Density (g/cm3) Oxide Formula Chloride Formula
Eka-silicon 72 5.5 EsO2 EsCl4 Germanium 72.3 5.47 GeO2 GeCl4
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History of the Periodic Table

• Dmitri Mendeleev (1834-1907)

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History of the Periodic Table

• Dmitri Mendeleev (1834-1907)
• The proposed table had three main problems
• If the order of increasing atomic mass was always
  followed, the elements properties did not always
  match up
• nickel and cobalt, iodine and tellurium had to be
  reversed
• Elements were discovered for which no space could
  be found
• holmium and samarium
• Elements in the same group were sometimes
  different in reactivity
• lithium,sodium vs. copper,silver

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History of the Periodic Table

• Henry Moseley (1887-1915)
• in 1913, found the atomic number of many elements
  through x-ray experiments
• ordering by atomic number instead of atomic mass
  eliminated the inconsistencies of Mendeleevs
  chart

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The Modern Periodic Table

• The long form

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The Modern Periodic Table

• The short form

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The Modern Periodic Table

• The short form
• Groups are numbered 1-18
• 1-2 and 13-18 are called main group elements
• Group 1 is the alkali metals
• Group 2 is the alkaline earth metals
• Group 16 is called the chalcogens
• Group 17 is called the halogens
• Group 18 is called the rare gases
• Group 3 and the lanthanoids are called the rare
  earth elements
• The f-elements are called the lanthanoids and
  actinoids
• 4-11 are called transition elements
• Group 11 is called the coinage metals

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Stability of the Elements

• Of the 112 known elements, only 81 are stable
• no stable isotopes exist for the elements above
  bismuth (nuclear repulsive forces)

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Stability of the Elements

• Nuclear proton and neutron configurations
• the protons and neutrons in a nucleus come
  together in layers to form nucleons
• the filling order is 1s, 1p, 2s, 1d
• completed levels contain 2, 8, 20, 28, 50, 82,
  and 126 nucleons
• magic numbers of stability

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Stability of the Elements

• Magic numbers were postulated by Maria
  Goeppert-Mayer and Hans Jensen
• 1963 Nobel Prize in physics

Maria Goeppert-Mayer (1906-1972)
J. Hans D. Jensen (1907-1973)
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Stability of the Elements

• Magic numbers directly relate to stable
  isotopes
• tin has 50 protons, and the most stable isotopes
  (10)
• there are seven different elements with stable
  isotopes containing 82 neutrons
• there are six different elements with stable
  isotopes containing 50 neutrons

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Stability of the Elements

• Doubly-magic nuclei are the most stable
• helium-4 has 2 protons and 2 neutrons
• oxygen-16 has 8 protons and 8 neutrons
• calcium-40 has 20 protons and 20 neutrons
• lead-208 has 82 protons and 126 neutrons

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Stability of the Elements

• Even numbers of protons produce more stable
  nuclei due to spin-pairing

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Classifications of Elements

• Commonly classified by phase at SATP
• standard ambient temperature (25C)
• standard ambient pressure (100 kPa)
• Among the elements, only 2 are liquids and 11 are
  gases

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Classifications of Elements
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Classifications of Elements

• Metals
• usually solids (except Hg)
• high 3-d electrical conductivity at SATP
• good thermal conductivity
• usually ductile and malleable
• tendency to form ionic bonds

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Classifications of Elements

• Nonmetals
• solids, liquids, and gases
• poor conductivity at SATP (except graphite)
• tendency to form covalent bonds
• Metalloids (semimetals)
• a mixture of both metallic and nonmetallic
  properties

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Classifications of Elements
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Periodic Properties

• Atomic radius
• covalent radius, rcov
• half-distance between the nuclei of two atoms
  which are covalently bound
• van der Waals radius, rvdw
• half-distance between nuclei in atoms of two
  neighboring molecules
• metallic radius
• half-distance between nuclei of two neighboring
  atoms in the solid metal

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Periodic Properties

• Atomic radius
• radii generally decrease from left to right in a
  row and increase down a group in the periodic
  table

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Periodic Properties

• Atomic radius
• radii generally decrease from left to right in a
  row and increase down a group in the periodic
  table
• an increase in the effective nuclear charge,
  Zeff, across the row causes a contraction in the
  atomic radius
• down a group, orbitals are larger and Zeff is
  smaller causing a general increase in the atomic
  radius

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Slaters Rules

• Effective Nuclear Charge, Zeff and the actual
  nuclear charge, Z, are related
• Zeff Z - ?
• ? is called Slaters screening constant

John C. Slater (1900-1976)
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Slaters Rules

• ? can be calculated according to 4 rules
• All electrons in orbitals of greater principal
  quantum number contribute zero
• Each electron in the same principal quantum
  number contributes 0.35, except when the electron
  studied is in a d or f orbital, then those in the
  s and p orbitals count 1.00 each
• Electrons in the (n-1) principal quantum level
  contribute 0.85 each, except when the electron
  studied is in a d or f orbital, then they count
  1.00 each
• All electrons in the lesser principal quantum
  levels count 1.00 each

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Slaters Rules

• Example
• Calculate Zeff on one of the 2p electrons in the
  oxygen atom (1s22s22p4).
• ? (2 ? 0.85) (5 ? 0.35) 3.45
• Zeff Z - ? 8 3.45 4.55

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Periodic Properties

• Ionization Energy
• energy required to remove an electron from an
  atom
• First ionization energy
• X(g) ? X(g) e-
• Second ionization energy
• X(g) ? X2(g) e-

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Periodic Properties

• Ionization Energy
• energies increase across a row and decrease down
  a group (due to Zeff)

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Periodic Properties

• Ionization Energy
• the most common ion can be found by looking at
  the ionization energies
• it is easier to remove electrons from the outer
  shell than the core electrons

Element 1st Ionization Energy 2nd Ionization Energy 3rd Ionization Energy 4th Ionization Energy
Sodium 495.8 4562 6910 9543
Magnesium 737.7 1451 7733 10540
Aluminum 577.5 1817 2745 11580
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Periodic Properties

• Electron Affinity
• energy change when an electron is added to an
  atom
• First electron affinity
• X(g) e- ? X-(g)
• Second electron affinity
• X-(g) e- ? X2-(g)

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Periodic Properties

• Electron Affinity
• electron affinity generally increases (energy
  becomes more negative) across a row and decreases
  down a column

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Biochemistry of the Elements

• Bioinorganic chemistry
• Essential elements (14) and Ultratrace elements
  (12)

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Biochemistry of the Elements

• Bertrands Rule