PERIODICITY

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PERIODICITY
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History of the Periodic Table

• 70 elements had been discovered by the
  mid-1800s, but until Dmitri Mendeleev, no one
  had a come with a way to organize the elements.
• Mendeleev came up with the first working system
  of filing the elements.
• He listed the elements in columns in order of
  increasing atomic mass, and then put columns
  together that were similar

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History of the Periodic Table

• Mendeleev left gaps in the table since there were
  no current elements that seemed to fit those
  spots
• Those elements were eventually discovered and
  they fit perfectly into an open spot.
• The 1st scientist that set the table in order of
  atomic number was Henry Moseley

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History of the Periodic Table

• The modern PT is arranged by increasing atomic
  number
• Increases from left to right, and top to bottom
• This establishes the periodic law
• When the elements are arranged in order of
  increasing atomic , there is a periodic
  repetition of their phys chem properties

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PNICOGENS
CHALCOGENS
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Periodic Properties

• An elements properties can go hand in hand with
  electron arrangement
• We can use an elements location on the PT to
  predict many properties.
• Atomic radius
• Electron affinity
• Electronegativity
• Ionization energy
• Ionic Size

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Periodic Properties

• The radius of an atom is defined by the edge of
  its last energy level.
• However, this boundary is fuzzy
• An atoms radius is the measured distance between
  the nuclei of 2 identical atoms chemically
  bonded together - divided by 2.

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Periodic Properties

• As we examine atomic radius from left to right
  across the PT we see a grad-ual decrease in
  atomic size.
• As e- are added to the s and p sublevels in the
  same energy level, they are gradually pulled
  closer to the highly positive nucleus
• The more e-s in the atom the less dramatic this
  trend looks

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Periodic Properties

• The change in atomic radii across the PT is due
  to e- shielding or to the effective nuclear
  charge
• As we move across the
  PT we are adding e- into
  the same gen- eral vol.
  in which case they will
  shield or interact
  with each other
  (repulsion)

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Periodic Properties

• We are also adding protons into the nucleus which
  increases the p-e- interaction (attraction)
• So the nucleus gains strength while the e- arent
  gaining much distance, so the atom is drawn in
  closer and closer to the nucleus.
• Decreasing the overall radius of the atom

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Periodic Properties

• How does the size of an atom change when
  electrons are added or removed?

As an Atom loses 1 or more electrons (becomes
positive), it loses a layer therefore, its radius
decreases.
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Periodic Properties

• How does the size of an atom change when
  electrons are added or removed?

As an Atom gains 1 or more electrons
(negative), it fills its valence layer,
therefore, its radius increases.
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Periodic Properties

• Elements in a group tend to form ions of the same
  charge.
• Modeled by electron configurations.

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Periodic Properties
He
O
He
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Periodic Trend of Ionic Charges
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The Transition Elements are almost unpredictable,
and sometimes have more than one possible charge
-- due to d orbitals --
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Tend to lose electrons to become positive
Tend to gain electrons to become negative
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Periodic Properties

• Another periodic trend on the table is ionization
  energy (a.k.a. potential)
• Which is the energy needed to remove one of an
  atoms e-s.
• Or a measure of how strongly an atom holds onto
  its outermost e-s.
• If the e-s are held strongly the atom will have a
  high ionization energy

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Periodic Properties

• The ionization energy is generally measured for
  one electron at a time
• You can also measure the amount of energy needed
  to reach in and pluck out additional electrons
  from atoms.
• There is generally a large jump in energy
  necessary to remove additional electrons from the
  atom.

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the amount of energy required to remove a 2p e
(an e- in a full sublevel) from a Na ion is
almost 10 times greater than that required to
remove the sole 3s e-
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Periodic Properties

• There is simply not enough energy available or
  released to produce an Na2 ion to make the
  compnd NaCl2
• Similarly Mg3 and Al4 require too much energy
  to occur naturally.
• Chemical formulas should always describe
  compounds that can exist naturally the most
  efficient way possible

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Periodic Properties

• Another periodic trend dealing with an e- is
  electron affinity
• Which is a measure of the ability of an atom to
  attract or gain an electron.
• Atoms that tend to accept an e- are those that
  tend to give a neg. charge.
• The closer to a full outer shell an atom has, the
  higher the affinity (more neg. the measurement)

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Periodic Properties

• An atoms ability to lose an e- or gain an e- can
  be used to understand the Octet Rule
• Octet Rule atoms tend to gain, lose, or share
  electrons in order to acquire a full set of
  valence electrons.
• 2 e- in the outermost s sublevel 6 e in the
  outermost p sublevel a full valence shell

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Periodic Properties

• Electronegativity is a key trend.
• It reflects the ability of an atom to attract
  electrons in a chemical bond.
• F is the most electronegative element and it
  decreases moving away from F.
• Electronegativity correlates to an atoms
  ionization energy and electron affinity

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BOILING POINT MELTING POINT VS. ATOMIC NUMBER
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Elemental Origins

• On the PT, only the elements through 92 are
  naturally occurring
• Elements are created through a process that took
  place in stars before our solar system came into
  being
• This process is called stellar nucleosynthesis.

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Elemental Origins

• Stars form when clouds of dust and hydrogen gas
  condense
• As this material condenses, pressure builds and
  temperatures reach millions of degrees
• The energy that is produced help stars live for
  billions of years
• The principle source of stellar energy is nuclear
  fusion

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Elemental Origins

• Fusion occurs when the nuclei of 2 or more atoms
  join together, to form the nucleus of a larger
  atom
• Typically 2 H nuclei combine to
  produce one
  He nucleus.

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Elemental Origins

• This is a type of nuclear rxn
• The mass of helium nucleus formed in the fusion
  process is slightly less than the mass of the
  four hydrogen nuclei that went into it.
• This small amount of missing mass is converted
  to energy according to Einsteins eqn Emc2

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Elemental Origins

• The mass of combining nuclei supplies the
  enormous energy that stars use to shine
• Nuclear fusion is not only the princ-iple source
  of energy for stars, but also the process by
  which elements heavier than H are created.
• The sun converts about 400 million tons of H into
  He every second

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Elemental Origins

• Other fusion rxns occur, depending on the mass of
  the star, the temp. of the star, the stage of
  its developmnt
• 2 He-4 atoms might combine to form Be-8 1 He-4
  1 Be-8 can fuse to form C-12
• When a star uses up all of the ele-ments that
  fuel its fusion, the star is no longer stable,
  it dies in a last great explosion

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Elemental Origins

• The elements that were formed within the star are
  flung into space
• When planets condense from this material, they
  take up the rich array of elements in the debris.
• Elements heavier than Fe were created by
  supernovas

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Elemental Origins

• On earth, which is considered a closed system,
  most elements are found in biogeochemical cycles.
• Elements are recycled through processes that
  keeps the amount of elements on earth constant.
• The big six cycles important for life are
  carbon, water, oxygen, phosphorus, nitrogen,
  sulfur

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Carbon Cycle
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Nitrogen Cycle
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Phosphorus Cycle
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Sulfur Cycle
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Oxygen Cycle
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Water Cycle
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Homemade Elements

• The first artificial isotope was created in 1919
• ? particles were being used to produce elements
  in the lab

• Scientists were taking a particles and colliding
  them with nitrogen atoms
• This led to the fusion of nuclei to form a
  synthetic isotope of oxygen

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Homemade Elements

• This was the first incident in which one element
  was transformed into another in a lab.
• Today, scientists change one element into another
  by bombarding nuclei with various small particles
• Protons, neutrons, alpha particles, and beta
  particles (fast moving electrons)

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Homemade Elements

• These nuclear bullets react with the nuclei
  they are aimed at forming iso-topes of naturally
  occurring elements
• Numerous synthetic elements are created with this
  method
• All of the elements with atomic s greater than
  92 but less than 101 were created with this
  process

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Homemade Elements

• The particles must be moving at extremely fast
  speeds and with a huge amount of energy in order
  to actually fuse rather than simply bouncing off
  of one another
• A device called a Particle Accelerator is used
  to accomplish this task

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Homemade Elements

• Elements with atomic 101 greater have been
  created by a colliding whole atoms rather than
  particles.
• To make the bigger atoms, special accelerators
  hurl entire atoms at one another
• Nobelium was created by crashing together
  Ca and Pb

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Homemade Elements

• The discovery of element 109 has been thoroughly
  verified and accepted
• It is extremely unstable
• Only 3 atoms of element 109 have ever been
  produced
• They only existed for a short time (.0034 seconds)

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Homemade Elements

• Scientists are hoping to discover other heavier
  atoms that might be more stable, because of the
  nature of their nuclei

• The atom smashers they plan to use are
  technological marvels, and there are only a few
  in the world

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Homemade Elements

• An accelerator is a linear or circular device
  that is used to increase the velocity of charged
  particles
• When the particle has been given a very
  high velocity and thus a very
  high energy, it is aimed at a target
  material.

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Homemade Elements

• The collision can help scientists discover new
  info. About the nucleus, sometimes create a
  heavier atom.

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Homemade Elements

• A typical accelerator is circular in shape
• Particles are accelerated by electric fields in
  several loca- tions around the ring.

• The particles path is confined to the ring by
  huge magnets.

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Homemade Elements

• The greater the energy of the collision between
  the accelerated particles with the target.
• The more scientists can learn about the structure
  and the behavior of the nucleus

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Collison of 2 Gold atoms
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