Unit One Chemistry

1
The Modern Periodic Table

• Unit One Chemistry Horsham College

Chapter 4 VCE Chemistry
2
Periodic Table Development

• No chemistry textbook, classroom, lecture theatre
  or research laboratory is complete without a copy
  of the periodic table of the elements.
• Chemists attempted to arrange the known elements
  in ways that revealed similarities between them.
• However, it required the genius of Mendeleev to
  see that arranging elements into patterns was not
  enough
• He realised that there was a natural plan in
  which each element has its allotted place, and
  this applies not only to the known elements but
  to some that were still undiscovered.
• Today there are 111 elements recognised by IUPAC,
  and these are usually displayed in the form of a
  matrix called a periodic table.

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What Patterns?

• Before the 1800s, scientists and alchemists did
  not consider the idea of patterns occurring
  between the known elements.
• Elements were considered unique and unrelated to
  any other element.
• Scientists who suggested that patterns may exist
  were ridiculed.
• Sodium and Potassium were discovered in the early
  1800s. Both have very similar properties.
• Empirical evidence later suggested that elements
  could be sorted in order of increasing atomic
  weight

• Elements were found to have repeating patterns.
  This is known as the periodic law.
• The advancing knowledge of the atomic model
  furthered chemists knowledge of elemental
  properties.

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Early classification -Antoine Lavoisier of 1789

• Antoine Lavoisier's 1789 classification of
  substances divided substances into four 'element'
  groups.
• The list contained substances that could not be
  broken down further.
• Acid-making elements Sulphur, Phosphorus,
  charcoal
• gas-like elements Light, caloric (heat), oxygen
• metallic elements cobalt, mercury, tin, copper,
  nickel, iron, gold, lead, silver, zinc,
  manganese, tungsten, platinum
• earthy elements lime, magnesia, barytes, azote,
  argilla, silex
• Lavoisier also formed the basis for the modern
  list of elements.

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Döbereiners Triads

• In 1829, German Johann Döbereiner discovered that
  groups of elements with similar chemical
  properties such as Lithium, Sodium and Potassium
  had a strange similarity.
• The average of the atomic weight of Lithium and
  Potassium was the same as the atomic weight of
  Sodium.
• The middle element in the triad had properties
  halfway between the properties of the other two.
• This pattern was replicated with Calcium,
  Strontium and Barium as well as Sulphur,
  Selenium, and Tellurium and also Chlorine,
  Bromine and Iodine.
• In addition, the densities of some of the triads
  followed the same relationship.
• These groups became known as "Döbereiner's
  triads".

Ca   Sr   Ba     (40 137) 2 88
40   88   137
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The Cylinder of Elements

• In 1862, Frenchman Alexandre de Chancourtois
  published a cylindrical arrangement of the
  elements (Also called the telluric screw).
• The elements, based on Oxygen-16, differed by 16
  in their atomic weight.
• Like Döbereiner, Chancourtois cylinder received
  little attention.

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The Law of Octaves

• English Chemist, John Newlands discovered that
  every eighth element had similar properties.
• He called this the law of octaves (Analogy with
  music).
• Newlands developed a table in which he placed
  elements with similar properties in the same
  collum.
• Unfortunately, his table was ridiculed by the
  Royal Society in 1864.

• However, while successful for some elements,
  Newlands' law of octaves failed for two reasons
• It was not valid for elements that had atomic
  masses higher than Ca.
• When further elements were discovered, such as
  the noble gases (He, Ne, Ar), they could not be
  accommodated in his table.

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John Newlands
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Questions 4.1

• Complete questions 1-4 on P. 72 of Nelson VCE
  Chemistry.

11
Mendeleev and Meyer

• Russian Dmitri Mendeleev and German Julius von
  Meyer went on to independently develop their
  versions of the periodic law.
• Both chemists produced remarkably similar results
  at the same time working independently of one
  another.
• Therefore, there has been some disagreement about
  who deserves credit for being the "father" of the
  periodic table

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Dmitri Mendeleev

• In 1869 Mendeleev arranged elements by atomic
  weights and properties.
• Mendeleev's periodic table of 1869 contained 17
  columns with two partial periods of seven
  elements each (Li-F Na-Cl) followed by two
  nearly complete periods (K-Br Rb-I).
• In 1871 Mendeleev revised the 17-group table with
  eight columns (the eighth group consisted of
  transition elements).
• This table exhibited similarities not only in
  small units such as the triads, but showed
  similarities in an entire network of vertical,
  horizontal, and diagonal relationships.
• The table contained gaps but Mendeleev predicted
  the discovery of new elements. 
• In 1906, Mendeleev came within one vote of
  receiving the Nobel Prize in chemistry.

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Julius von Meyer

• Julius von Meyer also developed a periodic table
  based on atomic masses, independently of
  Mendeleev.
• However, Meyer presented only 28 elements.
• Meyer had several inaccuracies and some elements
  were not included.
• Meyer was the first scientist to introduce the
  concept of valence as a periodic property.
• Also, Meyer never came to the idea of predicting
  new elements and correcting atomic weights.

• Only a few months after Mendeleev published his
  periodic table of all known elements (and
  predicted several new elements to complete the
  table, plus some corrected atomic weights), Meyer
  published a virtually identical table.

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Questions 4.2

• Complete questions 1-5 on P. 75 of Nelson VCE
  Chemistry.

17
Henry Moseley

• Moseley's research also showed that there were
  gaps in his table at atomic numbers 43 and 61
  which are now known to be radioactive and not
  naturally occurring.
• Following in the footsteps of Dmitri Mendeleyev,
  Henry Moseley also predicted new elements.

• Using atomic number instead of atomic mass as the
  organising principle was first proposed by the
  British chemist Henry Moseley in 1913.
• Before this discovery, atomic numbers were just
  sequential numbers based on an element's atomic
  weight.
• Moseley's discovery showed that atomic numbers
  had an experimentally measurable basis.
• Atomic number solved anomalies like Iodine, that
  has a higher atomic number than tellurium - so,
  even though he didn't know why, Mendeleev was
  right to place it after tellurium after all!

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Glenn Seaborg

• In the 1930s, the heaviest elements were being
  put up in the body of the periodic table
• Glenn Seaborg "plucked those out" while working
  with Fermi in Chicago, naming them the Actinide
  series.
• This later permitted proper placement of
  subsequently 'created' elements - the
  Transactinides, changing the periodic table yet
  again.
• These elements were shown separate from the main
  body of the table.
• The concept demonstrated how the heavy elements
  fit into the Periodic Table and thus demonstrated
  their relationships to the other elements.
• In addition to the discovery of transuranium
  elements,  Seaborg and his colleagues are
  responsible for the identification of more than
  100 isotopes of elements throughout the Periodic
  Table.

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The Periods of the Periodic Table

• The horizontal rows of the table are called
  periods.
• There are 7 periods.
• Elements in the same period have the same
  outermost occupied shell.
• Example Period 2 is filling the second shell.

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The Groups of the Periodic Table

• The vertical columns are called groups.
• Groups are numbered 1-18. This replaces the old
  system of I-VIII.
• Groups families have the same number of valence
  electrons in their valence (outermost) shell.

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• The periodic table groups are as follows (in the
  brackets are shown the old systems European and
  American)
• Group 1 (IA,IA) the alkali metals or hydrogen
  family/lithium family
• Group 2 (IIA,IIA) the alkaline earth metals or
  helium family/beryllium family
• Group 3 (IIIA,IIIB) the scandium family
• Group 4 (IVA,IVB) the titanium family
• Group 5 (VA,VB) the vanadium family
• Group 6 (VIA,VIB) the chromium family
• Group 7 (VIIA,VIIB) the manganese family
• Group 8 (VIII) the iron family
• Group 9 (VIII) the cobalt family
• Group 10 (VIII) the nickel family
• Group 11 (IB,IB) the coinage metals (not an
  IUPAC-recommended name) or copper family
• Group 12 (IIB,IIB) the zinc family
• Group 13 (IIIB,IIIA) the boron family
• Group 14 (IVB,IVA) the carbon family
• Group 15 (VB,VA) the pnictogens (not an
  IUPAC-recommended name) or nitrogen family
• Group 16 (VIB,VIA) the chalcogens or oxygen
  family
• Group 17 (VIIB,VIIA) the halogens or fluorine
  family
• Group 18 (Group 0) the noble gases or helium
  family/neon family

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Questions 4.3

• Complete questions 1-5 on P. 80 of Nelson VCE
  Chemistry.

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The Blocks of the Periodic Table (s-block)

• The s-block
• The s subshell of the valence shell is being
  filled.
• Since a s subshell holds 2 electrons, only 2
  groups of elements (Groups 1 2) are in this
  block
• Facts
• In the outermost occupied shell there are 1 or 2
  electrons in the s subshell but none in the p
  subshell.
• If the second outermost shell contains a d
  subshell, it does not contain electrons.

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The Blocks of the Periodic Table (p-block)

• The p-block
• The p subshell of the outermost shell is being
  filled.
• A p subshell can hold only 6 electrons, hence
  there are 6 groups in the p-block
• Facts
• In the outermost occupied shell there are 2
  electrons in the s subshell and 1 or more
  electrons in the p subshell.
• If the second outermost shell contains a d
  subshell, it is full.

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The Blocks of the Periodic Table (d-block)

• The d subshell is being filled.
• Due to the order of of energies of the subshells,
  this only occurs after the next shell has started
  to fill.
• A d subshell can hold 10 electrons, hence 10
  groups are found in the d-block.
• Metals in this block are collectively known as
  the transition metals.
• 3d subshell filling elements are called first
  transition series. 4d are second etc.
• Electron configuration
• In the outermost occupied shell the s subshell is
  full but there are no electons in the p subshell.
• The d subshell of the second outermost shell
  contain 1 or more electrons

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Questions 4.4

• Complete questions 1-5 on P. 83 of Nelson VCE
  Chemistry.

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The Noble Gases

• The noble gases are found in group 18 of the
  modern periodic table. They were not included in
  the original periodic table.
• Noble gases are found in minerals or in the
  atmosphere in trace amounts.
• Noble gases are un-reactive (inert) due to having
  a full outer shell.
• Henry Cavendish, in 1784, placed some air and
  pure oxygen into a U-shaped tube that contained
  mercury.
• He then added some salts and a base to the
  mercury. Cavendish used a electric discharge to
  start the reaction.
• These reactions removed the nitrogen and oxygen
  from the air.
• Surprisingly a bubble remained in the top of the
  tube.
• This unreactive bubble was called Cavendishs
  bubble.
• More than 100 years, this bubble was named Argon
  meaning Greek for lazy one.

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Rayleigh and Ramsey

• In the late nineteenth century, Lord Rayleigh and
  William Ramsay theorised that the nitrogen
  extracted from air was associated with another
  gas, argon.
• With this discovery, they realized that a whole
  class of gases was missing from the periodic
  table.
• Eventually all the known noble gases except for
  helium were discovered in the air, with argon
  being much more common than the others, and the
  table was completed.
• Helium was detected spectrographically in the Sun
  in 1868. The isolation of helium on Earth had to
  wait until 1895.
• Radon was isolated and studied in 1910 after many
  years of investigating by Ramsey. Radon is
  radioactive.

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Elements known before 1700
Elements known before 1700, plus those discovered
between 1700 and 1799
Elements known before 1800, plus those discovered
between 1800 and 1899
Elements known before 1900, plus those discovered
between 1900 and 2005
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The Missing Elements

• By 1925, 88 out of the 92 naturally occurring
  elements had been identified.
• Elements 43 (Technetium) ,61 (Promethium), 85
  (Astatine) and 87 (Francium) were missing.
• All are radioactive with very short half-lives.
• 61,85 and 87 have been identified in decaying
  uranium. All are extremely rare.
• 43 has only been produced synthetically.
• The periodic table is now complete!

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Alternative Tables The periodic spiral of
Professor Thoedor Benfey.
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Alternative Tables Albert Tarantolas orbital
periodic table.
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Alternative Tables Alexander Arrangement of the
Elements
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Stowes Arrangement
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Questions 4.5

• Complete questions 1-4 on P. 86 of Nelson VCE
  Chemistry.

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Review Questions

• Complete questions 1-8 on P. 88-89 of Nelson VCE
  Chemistry.