Atomic Structure

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Atomic Structure
2
History of Parts of the Atom

• Electronsfound by J.J.Thompson, using a Cathode
  Ray Tube, which showed that heated elements give
  off a stream of particles, negatively charged
  since they were attracted to a positive plate.
  Called electrons, very small, only 1/1800 of
  other atomic particles

3
History of Parts of the Atom

• Nucleusfound by Ernest Rutherford using a stream
  of nuclear particles shot at a piece of gold
  foilmost of them went straight through, but some
  were deflected and even reflected. This showed a
  relatively large positively charged mass at the
  center of the atom. Others found within that
  nucleus were two other particles, the proton and
  the neutron

4
Atomic Particles

• Electronsnegatively charged, very small mass,
  outside the nucleus in cloudlike orbits
• Protonpositive charge equal in value to electron
  charge, mass 1 AMU (atomic mass unit) is the
  basis for identity of atoms
• Neutronsprovide mass and the force to keep the
  nucleus together, no charge, mass 1 AMU

5
Identifying Atoms

• The nuclide designation gives information about
  any atom
• Atomic numbernumber of protons
• Mass numbersum of protons and neutrons

Number of neutrons is Mass - Atomic , in this
case, 12-66 neutrons
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Isotopes and Atomic Weight

• Since only protons determine the identity of an
  element, there may be more than one possible
  weight for an atom of an element if there are
  different numbers of neutrons. Such different
  nuclides are called isotopes
• 6p 6n 6p 8n
• Both are carbon

7
Isotopes and Atomic Weight

• Since there are more than one possible weight for
  the atoms of elements, we need a way to find out
  what an average atom of any element weighsthis
  is done with a machine called a mass
  spectrometer, which finds not only the masses of
  atoms but also how common each type is. Using
  that information, relative atomic masses can be
  calculated

8
Isotopes and Atomic Weight

• Process of finding Atomic Weight
• Get the mass of each isotope and its percent
• Multiply each mass by the percent as a decimal
• Add the results
• Example Cl-35 mass 35.0 75.53
• Cl-37 mass 37.0 24.47
• (35.0 x 0.7553) (37.0 x 0.2447) 35.5
• This is the weight in the periodic table.

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BONUS QUIZ!!!!

• If Si-28 is 92.21 , Si-29 is 4.70 and
  Si-30 is 3.09 , what is the relative atomic
  weight of Silicon??
• If you have , how many neutrons,
  protons, and electrons?

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HOMEWORK!!!

• p. 82 CYU all
• p. 84 CYU
• p. 99ff 3, 5, 6, 7, 8, 12, 37

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Electron Configuration

• The behavior of atoms depends upon where the
  electrons are surrounding the atom.
• Electrons
• are at specific distances
• are in specific energy levels
• have different potential energies
• Light and other electromagnetic radiations come
  when electrons move between these levels

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Quantum Mechanics

• Our present ideas about where electrons are have
  been developed by observing the effects of energy
  on atoms. Quantum mechanics explains the shape,
  direction, and energies of electron orbitals
  around the nucleus. This is done with some
  extremely sophisticated math

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Atomic Orbitals

• Orbitals are areas of space where the math has
  calculated a 90 probability of finding
  electrons. Four shapes have been observed to
  contain electrons, and these are designated s, p,
  d, and f.
• These orbital shapes have specific numbers of
  orbitals within them s-1 p-3 d-5 f-7 , and
  each of these orbitals is limited to two
  electrons only. This rule is called the Pauli
  exclusion principle

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p
s
f
d
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Electron Arrangement

• How electrons fit into the atom is written in two
  different ways, Electron Configuration notation
  and orbital notation
• EC examplelist levels, sublevels, and numbers of
  electrons for atoms
• 1s2 2s2 2p1 because it has 5 electrons

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Electron Arrangement

• It is sometimes easier to use the periodic table
  to find electron configuration

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Examples
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Orbital Notation

• This type of notation uses boxes or circles to
  represent the orbitals and arrows to represent
  electrons. To shorten these, we use a special
  shortcut, called Previous Noble Gas
  Configuration

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Examples
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Electron Configuration Rules

• You may have noted the difference which happens
  in the middle and bottom of the periodic table,
  where a level number for a sublevel is out of
  order.
• The rules help to understand this
• 1. Aufbau principleelectrons must go into
  lowest energy levels firstthis is why 4s is
  before 3d
• 2. Hunds rulewhen more than two orbitals of
  the same energy exist, fill them up singly before
  doubling upOne in each before two in any

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Special Lecture Bonus!!

• Give Electron Configuration and Orbital Notations
  for
• Use the Noble Gas shortcut

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Ground and Excited States

• The normal position for each electron in an atom
  is called its ground state. From this position,
  it can absorb energy to jump to a higher, excited
  state
• If an electron absorbs enough energy, it can jump
  entirely out of the atom, creating a species with
  more protons than electrons, an ion. Ions can
  also be formed when an atom attracts extra
  electrons. In the first case, the ion is
  positive, in the second, the ion will be negative.

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Light From Atoms

• When electrons in an excited state drop back to
  their ground state, they emit energy as light or
  other EM radiation. Two special cases are
  fluorescence and phosphorescence
• 1. Fluorescence happens when the atoms give off
  light as they are exposed to radiationfluorescent
  lights use this
• 2. Phosphorescence happens when atoms give off
  light after the energy source is gone. This is
  how glow-in-the-dark items work.

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Homework!!

• P88 CYUall 3
• p101ff 16 acegi, 17, 19, 20

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Periodicity

• Chemical properties of elements apparently recur
  periodically. This is the basis of the periodic
  table. The reason for this recurrence is the
  similar arrangement of the last electrons in the
  configuration of two similar behaving elements.
• Li1s2 2s1 Similar outer (valence)
• Na1s2 2s2 2p6 3s1 configurations makes
  them
• K1s2 2s2 2p6 3s2 3p6 4s1 behave alike

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Periodic Table

• Parts of the Tablerows, columns
• Rows are called periods and contain elements
  with the same number of energy levels, filling
  their outer valence level until it reaches 8
  electrons (Ns2 Np6)
• Columns are called groups or families and
  contain elements with the same valence shell
  electron configurations. For this reason
  Elements in the same column do the same things,
  that is they behave very similarly

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Representative and Transition

• Representative elements are those in the s and
  p blocks in the table. They always behave
  according to their valence electron configuration
• Transition elements are those in d and f
  blocks. Since they have inner electrons which
  sometimes get into action with their valence
  electrons, they have unique behavior which has to
  be studied specially

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Special Groups

• Alkali metalsgroup 1, very reactive, giving up
  electrons easily to form 1 ions
• Alkaline earth metalsgroup 2, quite reactive,
  not as much as alkalis, form 2 ions
• Halogensgroup 7, readily accept electrons to
  form 1 ions. Of these F is the most reactive of
  all elements
• Noble gasescolumn 8, non-reactive gases, each
  with the optimum outer electron configuration
  imitated by other elements in making ionic and
  covalent compounds

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Sections of the Table

• Metalsprimarily on the left, most of the
  elements of nature are metals, give up electrons
  to form ions, conduct heat and electricity well
  as solids, are malleable and ductile and usually
  shiny
• Nonmetalson the right side and above the
  stair-like dividing line, take or share
  electrons, some are gases, all are poor or non
  conductors and brittle as solids
• Metalloidsalong the stair-line on both sides,
  can go either way, losing or gaining electrons,
  though most often act like non-metals,
  semi-conducting, useful in electronic applications

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Periodic Law

• Properties of the elements are a periodic
  function of their atomic number, which means that
  if you follow a property thru the periodic table,
  that property will recur in similar fashion every
  so often in the table

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Periodic Properties

• Atomic Radiusas you move down a column in the
  table, size increases due to adding a new energy
  level on the outside, like nesting dolls As
  you go across the table, additional protons cause
  additional attraction, pulling the outer
  electrons closer to the nucleus and reducing the
  atoms size. The smallest atoms in any row will
  be those on the far righta rule to follow is
  Lower Left Larger
• Metallic charactersame trend as above, tells how
  much an element behaves like a metal

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Periodic Properties

• Ionization Energythe energy necessary to remove
  one outer electron from an atom. Inverse
  relation to atomic radius, since an electron
  farther away would be easier to remove. This
  energy increases across the table and decreases
  within a groupLower Left Less
• Electron Affinitysame trend as ionization
  energy, is the amount of energy released when an
  atom gains an extra electron

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Elements Necessary for Life

• Only about 25 elements are found in living
  creatures, the organic elements, the
  macrominerals and the trace elements .
• The organic elements are found in all body
  tissues and are C, H, O, and N. The
  macrominerals, K, Mg, Na, Ca, P, S, and Cl, are
  important in the blood, bones and teeth. 14
  other elements are found only in very small
  amounts, but are important in enzymes, hormones,
  and other body chemicals, and are the trace
  elements.

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Homework!!

• p. 101ff
• 23, 24, 28, 29, 30, 31, 41