Bohr Atom The Planetary Model of the Atom Objectives:

Presentación del tema: "Bohr Atom The Planetary Model of the Atom Objectives:"— Transcripción de la presentación:

1 Bohr Atom The Planetary Model of the Atom Objectives:
To describe the Bohr model of the atom. To explain the relationship between energy levels in an atom and lines in an emission spectrum.

2 Bohr’s Model Nucleus Electron Orbit Energy Levels

3 Bohr Model of Atom e- e- e-
Increasing energy of orbits n = 3 e- n = 2 n = 1 e- e- In 1913, Niels Bohr proposed a theoretical model for the hydrogen atom that explained its emission spectrum. – His model required only one assumption: The electron moves around the nucleus in circular orbits that can have only certain allowed radii. – Bohr proposed that the electron could occupy only certain regions of space – Bohr showed that the energy of an electron in a particular orbit is En = – hc n2 where  is the Rydberg constant, h is the Planck’s constant, c is the speed of light, and n is a positive integer corresponding to the number assigned to the orbit. n = 1 corresponds to the orbit closest to the nucleus and is the lowest in energy. A hydrogen atom in this orbit is called the ground state, the most stable arrangement for a hydrogen atom. As n increases, the radii of the orbit increases and the energy of that orbit becomes less negative. A hydrogen atom with an electron in an orbit with n >1 is in an excited state — energy is higher than the energy of the ground state. Decay is when an atom in an excited state undergoes a transition to the ground state — loses energy by emitting a photon whose energy corresponds to the difference in energy between the two states. A photon is emitted with energy E = hf The Bohr model of the atom, like many ideas in the history of science, was at first prompted by and later partially disproved by experimentation.

4 Modelo de Bohr del átomo
El aumento de la energía De las órbitas n = 3 e- n = 2 n = 1 e- e- En 1913, Niels Bohr propuso un modelo teórico para el átomo de hidrógeno que explicó su espectro de emisión.          - Su modelo requiere sólo una hipótesis: El electrón se mueve alrededor del núcleo en órbitas circulares que pueden tener sólo permite ciertas radios.      - Bohr propuso que los electrones pueden ocupar sólo ciertas regiones del espacio      - Bohr demostró que la energía de un electrón en una órbita es                              En  HC = -                                             N2         donde es la constante de Rydberg, h es la constante de Planck, c es la velocidad de la luz, y n es un entero positivo se corresponde con el número asignado a la órbita. N = 1 corresponde a la órbita más cercana al núcleo y es la más baja de la energía. Un átomo de hidrógeno en esta órbita se llama el terreno estatal, los más estables, para que tengan átomo de hidrógeno. A medida que n aumenta, los radios de la órbita de los aumentos y de la energía que se convierte en órbita menos negativa. Un átomo de hidrógeno con un electrón en una órbita con n> 1 está en un estado excitado de energía es mayor que la energía de la tierra estatal. Decay es cuando un átomo en un estado excitado experimenta una transición hacia el terreno estatal pierde energía por emisión de un fotón cuya energía corresponde a la diferencia de energía entre los dos estados. Un fotón es emitido Con la energía E = hf El modelo de Bohr del átomo, al igual que en muchas de las ideas la historia de la ciencia, en la primera fue motivada por y más tarde parcialmente desmentida por la experimentación.

5 Cartoon courtesy of NearingZero.net

6 Development of the Atom

7 Development of the Atom

8 Planetary Model +

9 An unsatisfactory model for the hydrogen atom
According to classical physics, light should be emitted as the electron circles the nucleus. A loss of energy would cause the electron to be drawn closer to the nucleus and eventually spiral into it. Hill, Petrucci, General Chemistry An Integrated Approach 2nd Edition, page 294

10 Quantum Mechanical Model
Niels Bohr & Albert Einstein Modern atomic theory describes the electronic structure of the atom as the probability of finding electrons within certain regions of space (orbitals).

11 Development of Atomic Models
Thomson model In the nineteenth century, Thomson described the atom as a ball of positive charge containing a number of electrons. Rutherford model In the early twentieth century, Rutherford showed that most of an atom's mass is concentrated in a small, positively charged region called the nucleus. Bohr model After Rutherford's discovery, Bohr proposed that electrons travel in definite orbits around the nucleus. Quantum mechanical model Modern atomic theory described the electronic structure of the atom as the probability of finding electrons within certain regions of space.

12 Modern View The atom is mostly empty space Two regions Nucleus
protons and neutrons Electron cloud region where you might find an electron