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## 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.**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.)**• 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)