Atomic Structure and the Periodic Table

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Atomic Structure and the Periodic Table

• Chemistry
• Chapter 5

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Concepts That You Should Know

• Students know the nucleus of the atom is much
  smaller than the atom yet contains most of its
  mass.
• Students know the experimental basis for
  Thomson's discovery of the electron, Rutherford's
  nuclear atom, Millikan's oil drop experiment, and
  Einstein's explanation of the photoelectric
  effect.
• Students know the experimental basis for the
  development of the quantum theory of atomic
  structure and the historical importance of the
  Bohr model of the atom.

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Development of Atomic Models

• Ancient Greeks Materials could be divided into
  smaller particles the smallest particle is the
  atom
• John Dalton (1766 -1844) atom a solid
  indivisible mass atoms combined to form
  compounds
• J.J. Thomson (1856 -1940) plum-pudding model
  which included electrons
• Ernest Rutherford (1871 - 1937) positively
  changed nucleus in the center
• Niels Bohr (1885 -1962) electrons arranged in
  concentric paths around the nucleus
• Erwin Schrödinger (1887 -1961) Quantum
  mechanical model

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Atomic Scientists

• Ernest Rutherford
• Erwin Schrödinger
• John Dalton

• Niels Bohr
• J J Thomson

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Greeks

• Greek Philosopher Democritus (400 B.C.) proposed
  the first atomic theory
• The world was made up of two things, void and
  tiny particles called atoms.
• The Greek word atomos, means indivisible.
• Atoms were small and could not be destroyed.
• There was a different type of atoms for different
  materials. (ex. Atoms of air, atoms of rock,
  atoms of iron)
• Atoms of solids were rough and would not slide
  over each other, atoms of liquids were smooth and
  could move.
• Not supported by experimental evidence.

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John Daltons Atomic Theory

• 1. Elements are composed of atoms
• tiny, hard, unbreakable, spheres  
• 2. All atoms of a given element are identical
• all carbon atoms have the same chemical
  and physical properties  
• 3. Atoms of a given element are different from
  those of any other element
• carbon atoms have different chemical and
  physical properties than sulfur atoms
•  4. Atoms of one element combine with atoms of
  other elements to form compounds.
• Law of Constant Composition
• all samples of a compound contain the same
  proportions (by mass) of the elements
• Chemical Formulas
•  5. Atoms are indivisible in a chemical process.
• all atoms present at beginning are present
  at the end
• atoms are not created or destroyed, just
  rearranged
• atoms of one element cannot change into
  atoms of another element
• cannot turn Lead into Gold by a chemical reaction
  

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Rutherfords Gold Foil Experiment
http//wps.prenhall.com/wps/media/objects/602/6165
16/Chapter_02.html
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Rutherford Gold Foil Experiment

• Experimental Data
• Over 98 of the _ particles went straight through
  
• About 2 of the _ particles went through but were
  deflected by large angles
• About 0.01 of the _ particles bounced off the
  gold foil

• Rutherford's Nuclear Model
• 1. The atom contains a tiny dense center called
  the nucleus
• (the volume is about 1/10 trillionth the
  volume of the atom)
• 2. The nucleus is essentially the entire mass of
  the atom
• 3. The nucleus is positively charged (the amount
  of positive charge of the nucleus balances the
  negative charge of the electrons)
• 4. The electrons move around in the empty space
  of the atom surrounding the nucleus

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J. J. Thomson

• On April 30, 1897, Thomson announced that the
  cathode rays consisted of negatively charged
  particles, which represented fundamental
  particles of matter. He is generally credited
  with the discovery of the electron.   He was
  awarded with the Nobel Prize in Physics in 1906.
• J.J. Thomson is also remembered for his
  "plum-pudding" model of the atom, which suggested
  a solid atom with positively and negatively
  charged particles evenly distributed throughout
  the mass of the atom.

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JJ Thomsons Plum Pudding
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J J Thomsons Experiment

• Cathode Ray Experimental Results
• 1) If an object is placed in the path of the
  cathode ray, a shadow of the object is cast on
  the glowing tube wall at the end. This showed
  that the cathode rays traveled in straight lines.
• 2) The cathode ray can push a small paddle wheel
  up an incline, against the force of gravity. This
  showed that the cathode ray carried energy and
  could do work.
• 3) The cathode ray is deflected from a straight
  line path by a magnetic field, suggesting that
  the two were related in some way.
• 4) Although there was some speculation that the
  cathode rays were negatively charged, it is not
  shown to be true by experiment until 1895, just
  two years before Thomson announces the electron.
• 5) J.J. Thomson is the first individual to
  succeed in deflecting the cathode ray with an
  electrical field. He did so in 1897. The cathode
  rays bend toward the positive pole, confirming
  that cathode rays is negatively charged.

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Bohr Atom

• Niels Bohr, a Danish physicist described the
  hydrogen atom in terms of electrons in energy
  levels.
• Bohrs model of the hydrogen atom is often called
  the planetary model.
• It describes the atom as a nucleus with a
  positive charge with negatively charged electrons
  orbiting the nucleus as planets orbit the sun.

• http//www.cbu.edu/mcondren/bohratom.htm

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Quantum Theory

• The protons and neutrons in the nucleus take up
  very little volume but contain essentially all
  the atoms mass. A number of electrons equal to
  the number of protons move around the nucleus and
  account for most of the atoms volume.
• The energy that an electron possess determines
  the space that it occupies.

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Quantum Mechanical Model

• Quantum Mechanical Model
• A more complicated model of the atom emerged
  later in the 1900s in order to explain the
  observed spectra of other elements. It is based
  on probability and the mathematics of waves.

• Atomic Model

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Quantum Theory
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Atomic Particles

• Nucleus contains protons and neutrons
• Proton is a positive particle with the mass of
• 1 amu
• Neutron is a neutral particle (no charge) with
  the mass of 1 amu
• Electrons
• Found in energy levels outside the atom.
• Lowest energy electrons closet to the nucleus and
  highest energy electrons away from the nucleus.

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Calculating Protons, Electrons and Neutrons

• The number of protons (p) charge is determined
  by the atomic number.
• The number of electrons (e -) in an atom, always
  equals the number of protons, thus is also
  determined by the atomic number.
• To determine neutrons, subtract the atomic number
  (p) from the atomic mass (p and n o).

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Isotopes

• Isotopes are forms of the same atom that and
  therefore have the same number of protons and
  electrons but have different masses.
• The difference in mass is caused by a gain or
  loss of neutrons.

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www.molres.org/ MRI_Downloads.html
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The Periodic Table and The Elements

• The periodic table displays the elements in
  increasing atomic number and shows how
  periodicity of the physical and chemical
  properties of the elements relates to atomic
  structure. As a basis for understanding this
  concept
• Students know how to relate the position of an
  element in the periodic table to its atomic
  number and atomic mass.
• Students know how to use the periodic table to
  identify metals, semimetals, nonmetals, and
  halogens.
• Students know how to use the periodic table to
  identify alkali metals, alkaline earth metals and
  transition metals, trends in ionization energy,
  electronegativity, and the relative sizes of ions
  and atoms.
• Students know how to use the periodic table to
  determine the number of electrons available for
  bonding.
• Students know the nucleus of the atom is much
  smaller than the atom yet contains most of its
  mass.
• Students know how to use the periodic table to
  identify the lanthanide, actinide, and
  transactinide elements and know that the
  transuranium elements were synthesized and
  identified in laboratory experiments through the
  use of nuclear accelerators.
• Students know how to relate the position of an
  element in the periodic table to its quantum
  electron configuration and to its reactivity with
  other elements in the table.

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Development of the Periodic Table

• Demitri Mendeleev (1834 -1907)
• First arrangement of the periodic table
• In the late 1860's, Mendeleev began working on
  his great achievement the periodic table of the
  elements.
• By arranging all of the 63 elements then known by
  their atomic weights, he managed to organize them
  into groups possessing similar properties.
• Where a gap existed in the table, he predicted a
  new element would one day be found and deduced
  its properties.
• http//corrosion-doctors.org/Biographies/Mendeleev
  Bio.htm

englishrussia.com/images/mendeleev_house/0.jpg
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Information from the Periodic Table
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Determining Atomic Particles
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Groups on the Periodic Table

• 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. Every element
  in the first column (group one) has one electron
  in its outer shell. Every element on the second
  column (group two) has two electrons in the outer
  shell. As you keep counting the columns, you'll
  know how many electrons are in the outer shell.
  There are some exceptions to the order when you
  look at the transition elements, but you get the
  general idea.

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Groups or Families of Elements

• Usually, the columns of the periodic table are
  used to define families or groups. The inert
  gases are all located in the far right column of
  the table. That column is labeled Group Zero.
• The thing to remember is... A family of elements
  can be found in several ways. You need to run
  tests and study the elements to determine their
  properties. Only after that testing, can you
  determine what family an element belongs in.
  EXAMPLES OF FAMILIES - Alkali Metals-
  Alkaline Earth Metals- Transition Metals-
  Halogen Gases- Inert Gases (Noble Gases)

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Hydrogen and Helium

• Hydrogen and helium 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. 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.
• http//www.chem4kids.com/files/elem_pertable.html

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Periods on the Periodic Table

• The different rows of elements are called
  periods. 
• The period number of an element signifies the
  highest energy level an electron in that element
  occupies (in the unexcited state). 
• The number of electrons in a period increases as
  you move from left to right across the table.
• http//periodic.lanl.gov/
• Graphic from
• http//www.chem4kids.com/files/elem_pertable.html