Download Electron Configuration and Periodic Trends

PERIODICITY
Electron Configurations
• Don’t have to write out the entire
electron configuration.
• There is a short-cut:
– Keeps focus on valence electrons
– An atom’s inner electrons are
represented by the symbol for the
nearest noble gas with a lower atomic
number.
K: [Ar]4s1
Electron Configurations
For the element Phosphorus
-- 15 electrons
1s22s22p63s23p3
P: [Ne]
Must be a
Noble gas
(One just before
Element)
Electron Configurations
Let’s do a couple more:
Ba: [Xe]
2
6s
Hg: [Xe] 6s2 4f14 5d10
V: [Ar] 4s2 3d3
Exceptions to the order of filling
Electron Configurations
• The chemistry of an atom occurs at
the set of electrons called valence
electrons
• The valence electrons are electrons
in an atom’s highest energy level.
– For the Group – A elements, it is the
outermost s & p e- of the atom.
– Specifically the 2 s electrons + 6 p
electrons (octet electrons)
• The arrangement of the valence elead to the element’s properties.
History of the Periodic Table
• 70 elements had been discovered by
the mid-1800’s, 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
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
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
Periodic Properties
• An element’s properties can go hand
in hand with electron arrangement
• We can use an element’s location on
the PT to predict many properties.
–
–
–
–
–
Atomic radius
Electron affinity
Electronegativity
Ionization energy
Ionic Size
Periodic Properties
• The radius of an atom is defined by
the edge of its last energy level.
– However, this boundary is fuzzy
• An atom’s radius is the measured
distance between the nuclei of 2
identical atoms chemically bonded
together - divided by 2.
Periodic Properties
• As we examine atomic radius from left
to right across the PT we see a gradual 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
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 general vol. in which case
they will shield or
interact with each
other (repulsion)
Periodic Properties
– We are also adding protons into the
nucleus which increases the p+-einteraction (attraction)
• So the nucleus gains strength while
the e- aren’t gaining much distance,
so the atom is drawn in closer and
closer to the nucleus.
– Decreasing the overall radius of the
atom
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.
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.
Periodic Properties
• Elements in a group tend to form ions
of the same charge.
– Modeled by electron configurations.
K: [Ar]
4s
Loses 1
electron
[Ar]
Wants a full set of e-
4s
Periodic Properties
O: [He]
2s2
Wants a complete set
2p4
Gains
2 electrons
[He]
Periodic Trend of Ionic Charges
The Transition Elements are almost
unpredictable, and sometimes have
more than one possible charge -- due to
d orbitals --
Tend to lose
electrons to
become
positive
Tend to gain
electrons to
become
negative
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
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.
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-
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
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)
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
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
atom’s ionization energy and electron
affinity
BOILING POINT & MELTING POINT VS. ATOMIC NUMBER
INCREASES
INCREASES
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.
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
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.
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
Einstein’s eqn E=mc2
Elemental Origins
• The mass of combining nuclei
supplies the enormous energy that
stars use to shine
– Nuclear fusion is not only the principle 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
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 elements that fuel its fusion, the star is
no longer stable, & it dies in a last
great explosion
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
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
Homemade Elements
• The first artificial isotope was created
in 1919
–  particles were being used to
produce elements in the lab
• Scientists were taking  particles and
colliding them with nitrogen atoms
• This led to the fusion of nuclei to form
a synthetic isotope of oxygen
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)
Homemade Elements
• These “nuclear bullets” react with the
nuclei they are aimed at forming isotopes 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
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
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
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)
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
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.
Homemade Elements
• The collision can help scientists
discover new info. About the nucleus,
& sometimes create a heavier atom.
Homemade Elements
• A typical accelerator is circular in
shape
• Particles are accelerated by electric
fields in several locations around the ring.
• The particle’s path is
confined to the ring
by huge magnets.
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