Download a first “working” model for the atom

Section 3.2 Answers
1. Explain the main weakness with the Rutherford model of the atom and how Bohr
addressed it.
Answer: Rutherford model is not able to explain the stability of atom. Bohr presented a
brand new atomic theory that suggests that electrons revolve around the nucleus in
discrete shells and have discrete energy values. Because of this, they do NOT radiate
energy continuously, so they do not fall in the nucleus, and the atom is able to maintain
its stability.
2. Describe what happens when atoms or molecules absorb light.
Answer: Absorption of a photon of light promotes the molecule to an excited state.
3. Scientists use emission spectra to confirm the presence of an element in materials.
Explain why this is possible.
Answer: An emission spectrum is the electromagnetic radiation (EMR), such as visible light, a substance
emits. Every element gives off a unique fingerprint of light, so analyzing the frequencies of this light helps
identify the chemical that generated it. This procedure is called emission spectroscopy and is a very
useful scientific tool. It is used in astronomy to study the elements present in stars and in chemical
analysis.
5. Explain why the emission spectrum of an element depends on its arrangement of
electrons.
Answer: The energy of each electron in an atom depends on how strongly the electron is attracted by
the positive charge on the nucleus and on how much it is repelled by other electrons.
6. a) Every element exhibits unique line spectra.
b) The study of the spectral emission lines of distant galaxies and stars, fireworks etc.
c) Qualitative. Each element has unique line emission spectra.
8. a) Spectroscopy pertains to the dispersion of an object's light into its component
colors. By performing this dissection and analysis of an object's light, astronomers
can infer the physical properties of that object.
b) Spectroscopic studies were central to the development of quantum
mechanics and included Max Planck's explanation of blackbody radiation, Albert
Einstein's explanation of the photoelectric effect and Niels Bohr's explanation
of atomic structure and spectra.
9. a) The Main Points of the Bohr Model
The orbits of the hydrogen atom which an electron travels have a set size and energy level. Therefore,
the orbits are said to be quantized.
The size of the orbit's radius is directly proportional to the orbit’s energy state.
When an electron is in orbit the energy of the entire atom is at a constant rate.
When the electron transfers from one orbit another, this is when the energy level changes. This process
of the electron's movement from one orbit to another is called a 'jump'.
The jumps of an electron deal with the emission and absorption of photons. The ways these photons are
given off and taken in by the hydrogen's electron account for specific spectral lines of the hydrogen
spectrum which deals with the atomic spectra.
b) Successes and failures of the Bohr model
Successes:
- combining successfully Rutherford’s “solar system” model, with the Planck hypothesis on
the quantified energy states at atomic level + Einstein’s photons
- explaining the atomic emission and absorption spectra
- explaining the general features of the periodic table
- a first “working” model for the atom
Failures
- a mixture of classical and quantum ideas (electrons move classically on orbits, but their
possible energy states are quantified)
- could not account for the maximal electron numbers on one shell
- could not explain splitting of the spectral lines in magnetic fields
- only explained Hydrogen Spectra