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Lecture 14

CHEM 1201 Lecture Notes - Lecture 14: Schrödinger Equation, Principal Quantum Number, Supreme Headquarters Allied Powers EuropePremium

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CHEM 1201

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Chem 12 - Lecture 14 - Atomic Models
Atomic Models - The Bohr Model
Neil's Bohr, born in 1913, proposed the first modern model of the hydrogen atom. This
model similar to how planets orbit the sun..with some form of centrifugal force.
The model of course is incorrect. In that the centrifugal affect was made by the
electrostatic attraction +/- btw the lectron & protons. And another problem came with the
discovery of the wave properties of the electron.
The oscillation associated with waves would yield orbitals that fluctuated in energy and
imply that they are not quantized ie not possible.
Bohr did develop an equation that explained the visible spectrum of lines for the
hydrogen atom as the quantized absorption and emission of energy by atoms, when
electrons shift from one energy level to another level.
where RH is the Rydberg constant = 2.18 x 10-18J, h = 6.63 x 10-34J-s, v = frequency,
ni is the initial state (where you start) and nf is the final state (where you end).
Bohr's model, works well for hydrogen but not the rest of the periodic table; nor does it
help explain the electron's location in the atom (s).
Atoms of elements when subjected to certain excitation energies absorb some of this
They are promoted from a ground state (lower energy) to an excited state (higher
energy). When they relax back to a lower state, energy is given off.
Only photons at certain wavelengths are emitted for each element.
Therefore, each element has its own wavelength fingerprint (emission spectrum), which
is different from every other element
Why is this?, because every element has atomic orbitals (later) of slightly different
energies that are unique for each element
NOTE: The fact that the radiation is given off is not continuous, but occurs as narrow
lines implies that the emission and absorption process is quantized (a specific energy
correlating to a specific frequency).
Problems with Bohr’s Theory
1. Many additional properties of atoms could not be explained by Bohr’s Theory. Solving
these problems let to the development of modern quantum theory
2. 4 quantum numbers are needed to describe each electron where Bohr had 1.
3.. It became clear that electrons did not move in precise orbits.
4.. The shapes of the regions of space occupied by electrons could not be explained by
Bohr’s Theory.
5.. The arrangement of electrons in energy levels could not be explained by Bohr’s
Mechanical model of the atom
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