Periodic Table

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Periodic Table

• Done by John Tan Wen Yu

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History of the Periodic Table

• In 1789, Antoine Lavoisier published a list of 33
  chemical elements. Although Lavoisier grouped the
  elements into gases, metals, non-metals, and
  earths, chemists spent the following century
  searching for a more precise classification
  scheme.

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• In 1829, Johann Wolfgang Döbereiner observed that
  many of the elements could be grouped into triads
  (groups of three) based on their chemical
  properties.
• Lithium, sodium, and potassium, for example, were
  grouped together as being soft, reactive metals
• Döbereiner also observed that, when arranged by
  atomic weight, the second member of each triad
  was roughly the average of the first and the
  third. This became known as the Law of triads.

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• German chemist Leopold Gmelin worked with this
  system, and by 1843 he had identified ten triads,
  three groups of four, and one group of five.
• Jean Baptiste Dumas published work in 1857
  describing relationships between various groups
  of metals.

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• Although various chemists were able to identify
  relationships between small groups of elements,
  they had yet to build one scheme that encompassed
  them all
• German chemist August Kekulé had observed in 1858
  that carbon has a tendency to bond with other
  elements in a ratio of one to four.

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• Methane, for example, has one carbon atom and
  four hydrogen atoms. This concept eventually
  became known as valency
• In 1864, fellow German chemist Julius Lothar
  Meyer published a table of the 49 known elements
  arranged by valency
• The table revealed that elements with similar
  properties often shared the same valency

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• English chemist John Newlands published a series
  of papers in 1864 and 1865 that described his
  attempt at classifying the elements
• Russian chemistry professor Dmitri Ivanovich
  Mendeleev and Julius Lothar Meyer independently
  published their periodic tables in 1869 and 1870,
  respectively.

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• They both constructed their tables in a similar
  manner by listing the elements in a row or
  column in order of atomic weight and starting a
  new row or column when the characteristics of the
  elements began to repeat.
• The success of Mendeleev's table came from two
  decisions he made The first was to leave gaps in
  the table when it seemed that the corresponding
  element had not yet been discovered

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• With the development of modern quantum mechanical
  theories of electron configurations within atoms,
  it became apparent that each row (or period) in
  the table corresponded to the filling of a
  quantum shell of electrons.
• In the years that followed after Mendeleev
  published his periodic table, the gaps he left
  were filled as chemists discovered more chemical
  elements.

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• The first transuranic element to be discovered
  was neptunium, which was formed by bombarding
  uranium with neutrons in a cyclotron in 1939

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What is the Periodic Table?

• It is a tabular display of the chemical elements

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• Its layout has been refined and extended over
  time, as new elements have been discovered, and
  new theoretical models have been developed to
  explain chemical behaviour
• It is now ubiquitous within the academic
  discipline of chemistry, providing a useful
  framework to classify, systematize, and compare
  all of the many different forms of chemical
  behaviour

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• The table has found many applications in
  chemistry, physics, biology, and engineering,
  especially chemical engineering
• The current standard table contains 118 elements
  to date. (elements 1118).

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Description of the Periodic Table

• The layout of the periodic table demonstrates
  recurring ("periodic") chemical properties.
• Elements are listed in order of increasing atomic
  number (i.e., the number of protons in the atomic
  nucleus).
• Rows are arranged so that elements with similar
  properties fall into the same columns (groups or
  families).

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• In printed tables, each element is usually listed
  with its element symbol and atomic number many
  versions of the table also list the element's
  atomic mass and other information, such as its
  abbreviated electron configuration,
  electronegativity and most common valence
  numbers.

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• As of 2010, the table contains 118 chemical
  elements whose discoveries have been confirmed.
  Ninety-four are found naturally on Earth, and the
  rest are synthetic elements that have been
  produced artificially in particle accelerators.

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• The primary determinant of an element's chemical
  properties is its electron configuration,
  particularly the valence shell electrons.
• Note that as atomic number (i.e., charge on the
  atomic nucleus) increases, this leads to greater
  spin-orbit coupling between the nucleus and the
  electrons, reducing the validity of the quantum
  mechanical orbital approximation model, which
  considers each atomic orbital as a separate
  entity.

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Classification

• Groups
• A group or family is a vertical column in the
  periodic table.
• Groups are considered the most important method
  of classifying the elements. In some groups, the
  elements have very similar properties and exhibit
  a clear trend in properties down the group.
• e.g., the alkali metals, alkaline earth metals,
  halogens, pnictogens, chalcogens, and noble
  gases.

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• Periods
• A period is a horizontal row in the periodic
  table.
• Although groups are the most common way of
  classifying elements, there are some regions of
  the periodic table where the horizontal trends
  and similarities in properties are more
  significant than vertical group trends.

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• Blocks
• Because of the importance of the outermost shell,
  the different regions of the periodic table are
  sometimes referred to as periodic table blocks,
  named according to the subshell in which the
  "last" electron resides.

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• Other
• The chemical elements are also grouped together
  in other ways
• Some of these groupings are often illustrated on
  the periodic table, such as transition metals,
  poor metals, and metalloids
• Other informal groupings exist, such as the
  platinum group and the noble metals

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A simpler description of its characteristics

• Period
• When you look at a periodic table, each of the
  rows is considered to be a different period
• In the periodic table, elements have something
  in common if they are in the same row

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• Groups
• When a column goes from top to bottom, it's
  called a group.
• The elements in a group have the same number of
  electrons in their outer orbital.

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• Two at the top
• Hydrogen (H) and helium (He) are special elements
  
• Hydrogen can have the talents and electrons of
  two groups, one and seven
• To scientists, hydrogen is sometimes missing an
  electron, and sometimes it has an extra
• Helium is different from all of the other
  elements

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• It can only have two electrons in its outer shell
• Even though it only has two, it is still grouped
  with elements that have eight (inert gases).

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• The elements in the center section are called
  transition elements. They have special electron
  rules

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Periodicity of chemical properties

• The main value of the periodic table is the
  ability to predict the chemical properties of an
  element based on its location on the table.
• It should be noted that the properties vary
  differently when moving vertically along the
  columns of the table than when moving
  horizontally along the rows.

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• Trends of groups
• Modern quantum mechanical theories of atomic
  structure explain group trends by proposing that
  elements within the same group have the same
  electron configurations in their valence shell,
  which is the most important factor in accounting
  for their similar properties.

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• Elements in the same group also show patterns in
  their atomic radius, ionization energy, and
  electronegativity.
• From top to bottom in a group, the atomic radii
  of the elements increase.
• With more filled energy levels, valence electrons
  are found farther from the nucleus.

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• From the top, each successive element has a lower
  ionization energy because it is easier to remove
  an electron since the atoms are less tightly
  bound
• Similarly, a group will also see a top to bottom
  decrease in electronegativity due to an
  increasing distance between valence electrons and
  the nucleus

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• Trends of periods
• Elements in the same period show trends in atomic
  radius, ionization energy, electron affinity, and
  electronegativity
• Moving left to right across a period, atomic
  radius usually decreases
• This occurs because each successive element has
  an added proton and electron which causes the
  electron to be drawn closer to the nucleus

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• This decrease in atomic radius also causes the
  ionization energy to increase when moving from
  left to right across a period
• The more tightly bound an element is, the more
  energy is required to remove an electron.
  Electronegativity will increase in the same
  manner as ionization energy because of the amount
  of pull that is exerted on the electrons by the
  nucleus

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• Metals (left side of a period) generally have a
  lower electron affinity than nonmetals (right
  side of a period) with the exception of the noble
  gases.

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Some uses of the periodic table

• The noble gases are used in industry in arc
  welding, to dilute the oxygen in deep-sea divers'
  gas tanks, and to fill light bulbs.
• Argon is used in arc welding and in common light
  bulbs, as it does not react with the metal at
  high temperatures.

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• Helium is used for diluting the pure oxygen in
  deep-sea diving tanks because the helium has a
  low solubility in human blood
• Helium is also used to inflate the tires of large
  aircraft, weather balloons, and blimps because it
  is nonflammable.
• Neon is used in sign tubing because it glows
  bright red when electricity is passed through it.

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• Krypton and xenon are used in photographic flash
  units and in lighthouses, as running an electric
  current through either element generates a very
  bright light.

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References

• http//en.wikipedia.org/wiki/Periodic_table
• http//www.learner.org/interactives/periodic/group
  s4.html
• http//www.chem4kids.com/files/elem_pertable.html

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Thank You