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 come up 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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Periodic Table 101

• Most of the elements
  on the periodic table are metals
• 16 of the elements
  are classified as nonmetals
• There are 7 elements that cant
  be classified as metals or nonmetals,
  and they are called metalloids.
• The noble gases are the last column
  on the table and significant because they are
  chemically inert

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Periodic Table 101

• There are 2 elements that are liquid at room
  temperature (Br Hg).
• There are 11 gaseous elements (the
  noble gases, H, O, N, F, Cl)
• The rest of the elements are solids at room
  temperature
• Elements 1-92 are naturally occurring with the
  exception of Tc, the rest were manufactured with
  an atom smasher

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Periodic Table 101

• Hydrogen is the most abundant element in the
  universe
• Francium is the least abundant natural element
• The most abundant element on earth
  is Oxygen
• There are over 10,000,000 carbon
  compounds
• The most reactive element is fluorine

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Periodic Table 101

• The PT is organized into vertical columns called
  groups or families.
• There are 18 columns
• Each family contains elements with similar
  chemical characteristics
• Each element in a family has the same number of
  valence electrons
• This makes it somewhat predictable as to how the
  atom will behave in chemical reaction

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PNICOGENS
CHALCOGENS
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Periodic Table 101

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

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Periodic Table 101
He
O
He
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The Transition Metals are almost unpredictable,
and sometimes have more than one possible charge
-- due to the d orbitals --
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Periodic Trend of Ionic Charges
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Tend to lose electrons to become positive
Tend to gain electrons to become negative
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Periodic Table 101

• The horizontal rows of elements in the PT are
  called periods.
• Physical and chem characteristics change
  predictably across the period
• Elements close to each other tend to have similar
  characteristics, while elements farther apart
  become increasingly different

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Periodic Table 101

• The two sets of elements below the PT make up
  what are called the lanthanide and actinide
  series.
• They are metallic and radioactive and should be
  placed after elements 57 89

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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
• Ionic Size
• Ionization energy
• Electron affinity
• Electronegativity

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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 are
  being shielded
  or screened by interior
  electrons, but the
  shielding isnt
  increasing

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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

• 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

• 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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Electronegativity
Electronegativity
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Electronegativity
Electronegativity