Quantum Theory and the Atom

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Quantum Theory and the Atom

• Objectives
• AOD C.3.1 Define atomic radii, ionization
  energy, electronegativity, and energy levels.
• AOD C.3.2 Recognize periodic trends of elements,
  including the number of valence electrons, atomic
  size, and reactivity.

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Niels Bohr and Energy States

• Proposed a quantum model for hydrogen to explain
  its discontinuous emission spectrum
• Proposed that the hydrogen atom has only certain
  allowable energy states
• Ground state lowest allowable energy state
• Excited state when an atom gains energy

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Niels Bohr and Energy States (cont.)

• The smaller the electrons orbit, the lower its
  energy state, or level. (ladder rungs)
• Each energy level has a quantum number, n,
  applied to it. (ladder rungs)
• How many electrons does hydrogen have?
• In which orbit, or energy level, would you expect
  to find it?
• This would be hydrogens ground state.

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Niels Bohr and Energy States (cont.)

• Bohr assigned 7 energy levels to hydrogen.
• When energy is added to an atom (i.e., electric
  current in the lab), the electron moves to a
  higher-energy orbit (excited state.)
• How many spectral lines did you see for hydrogen?

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Niels Bohr and Energy States (cont.)

• Spectral lines are created by energy released as
  an electron moves from an excited state to a
  lower state.
• Why do we only see 4 spectral lines from H,
  instead of 7?
• Answer We only see the lines in the visible,
  ultraviolet, and infrared regions of the
  electromagnetic spectrum.

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Excited Elements Lab Review

• How many lines did hydrogen have?
• How many lines did helium have?
• How many lines did your unknown element have?
• Compare to next slide.

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Atomic Orbitals

• Def a 3-dimensional region around the nucleus
• Insert Fig. 5-13, P. 132
• The more dense the cloud, the higher the
  probability of finding an electron there.

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Hydrogens Atomic Orbitals

• As you can see, the boundaries are fuzzy, so
  there is no defined orbital path or size.
• Chemists draw an orbitals surface to represent
  the area in which an electron spends 90 of its
  time.
• Figure 5-13b shows the boundaries of the
  hydrogen electrons lowest-energy orbit .

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Hydrogens Atomic Orbitals (cont.)

• Bohr quantum numbers (n)
• Quantum mechanical model principal quantum
  numbers (n) principal energy levels.
• As n increases, the orbital becomes larger, the
  electron spends more time farther from the
  nucleus, and the atoms energy level increases.
  (see Fig. 5-15a, p.133)

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Hydrogens Atomic Orbitals (cont.)

• Again, 7 energy levels have been detected for
  hydrogen, but in which level would the electron
  be found if the atom is in its ground state?
• Principal energy levels contain energy sublevels
  s, p, d, and f, as follows

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Hydrogens Atomic Orbitals (cont.)

• Insert table 5-2, P.134
• Relate to Electron Configuration Concert
  activity.

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Hydrogens Atomic Orbitals (cont.)

• How many sections have a Row 1?
• How many boxes in each row of Section s?
• How many seats in each box?
• How many sections have a Row 2?
• Which sections are they?
• How many boxes in each row of Section p?
• How many seats in each box?

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Hydrogens Atomic Orbitals (cont.)

• Row (principal energy level) n
• of sections (sublevels) with that Row
  increases by 1 each time
• of boxes (orbitals) in each Row n2
• How many seats are in each box???
• So of seats (electrons) in each Row
  (including ALL sections) 2n2
• Insert Table 5-2 again.

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What Do You Know?

• The lowest allowable energy state of an atom is
  called its ____________.
• According to Bohrs atomic model, the larger an
  electrons orbit, the _______ the atoms energy
  level.
• What did Bohr propose happens when energy is
  added to a hydrogen atom?
• Study Guide p.28 (15-22, omit 17)