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PERIODICITY

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Title: 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
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