27.1.3 Observe and explain Alpha particles are elementary particles emitted by s

Question

27.1.3 Observe and explain Alpha particles are elementary particles emitted by some materials, such as uranium; an alpha particle has an electric charge of +2e and the mass of a helium atom. To help determine atomic structure, Rutherford and his graduate students shot alpha particles at a thin sheet of mica or metals. They looked at places where the particles hit a fluorescent screen after passing through the thin sheets. They also looked for alpha particles that possibly bounced backward off the thin sheet (on the same side as the incoming alpha particles). They observed that most alpha particles moved through the sheet with minor deflection. However, a small frac- tion of the alpha particles bounced backward. At this time physicists already knew that atoms are electrically neutral and contain several electrons. Electrons were known to have a very small mass, much smaller than the mass of the atom. What could Rutherford suggest about the distribution of the positive charge in the atom to explain his experiments? 27.1.6 Explain Does the planetary atomic model proposed by Rutherford and information about the radiation of the electromagnetic waves that you learned in Chapter 24 (any accelerated electrically charged particle emits electromagnetic radiation) a. Produce a stable model for the hydrogen atom with one electron circling around the nucleus? Explain b. Explain the lines in a spectrum of hydrogen (see Activity 27.1.1) 27.1.7 Evaluate In 1913 Niels Bohr devised a solution to save Rutherford's planetary model from collapsing and to explain the line spectrum of hydrogen. He suggested that electrons are charged particles, which when bound in an atom behave in this way: they obey Newton's laws, interact with the nucleus via Coulomb forces, and do not radiate energy when the atoms are in the preferred energy states (called stable energy states) even though electrons in those atoms are moving in a circle. But as a trade off, atoms can only have energies corresponding to the energies of the stable states. To change its state, the atom needs either to emit a photon (when the energy decreases), or to absorb a photon (when the energy increases). Discuss how this model helps to explain observations of gas spectra and observations conducted by Rutherford and his colleagues

Explanation / Answer

27.1.3 Rutherform in his faous alpha particle scattering concluded that, since most of the alpha particels goes undeflected or with very less deflection, that indicates that all positive charge is present in a very tiny space(called Nucleus) inside atom.

27.1.6

(a) Rutherford Planetary Model couldn't succeed since It violeted the Maxwells theory, that any charge particle having acceleration should radiate EM wave, and therefore lose its energy

(b) Line Spectra of a single Atom like Hydrogen indicates Discrete spectra having discrete wavelength pattern called Lyman, Balmer, Paschen, Brackett, Pfund Series, which is in contrast to Continuous spectra observed from condensed matter.

27.1.7. Neils Bohrs has taken the advantage of Quantum Physics , and he has combined it with Classical Mechanis, suggesting that electron will not emit EM wave, until it is in stable orbits,where Angluar Momentum is quantised. therefore Elctron has discrete Energy Levels . If electron is in some higher excite state, It will return back to ground state by releasing a Quanta (Photon) of energy having energy equal to the difference of Energy of 2 states.

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