Transcript Quantum theory and the Atom (Section 5.2)

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.
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
Niels Bohr and Energy States
(cont.)
• The smaller the electron’s 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 hydrogen’s ground state.
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?
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.
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.
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.
Hydrogen’s Atomic Orbitals
• As you can see, the boundaries are fuzzy,
so there is no defined orbital path or size.
• Chemists “draw” an orbital’s surface to
represent the area in which an electron
spends 90% of its time.
• Figure 5-13b shows the “boundaries” of
the hydrogen electron’s lowest-energy
orbit .
Hydrogen’s 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 atom’s
energy level increases. (see Fig. 5-15a,
p.133)
Hydrogen’s 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:
Hydrogen’s Atomic Orbitals
(cont.)
• Insert table 5-2, P.134
• Relate to Electron Configuration Concert
activity.
Hydrogen’s Atomic Orbitals
(cont.)
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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?
Hydrogen’s 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.
What Do You Know?
• The lowest allowable energy state of an
atom is called its ____________.
• According to Bohr’s atomic model, the
larger an electron’s orbit, the _______ the
atom’s energy level.
• What did Bohr propose happens when
energy is added to a hydrogen atom?
• Study Guide: p.28 (15-22, omit 17)