Electron Configurations Another Look at the Atom

Exciting Electrons? If an electron receives the right “quanta” of energy it becomes excited. Possible forms of energy include heat and electricity. To return to a more stable place electrons release the energy in the form of light.

Continuous Spectrum Passing white light through a prism or a diffraction grating separates the light into all the colors of the visible spectrum. Note: there are no dark spots, only color.

A larger picture of a continuous spectrum

Line Spectrum Each element gives off its own characteristic colors when excited. Passing this light through a prism produces a few colored lines (emitted energy) and black regions (absorbed energy).

These are emission spectra and are unique to each element.

1913 proposed Planetary model Niels Bohr (1885-1962) 1913 proposed Planetary model

Bohr’s Model of the Hydrogen Atom Recall Rutherford’s model of the atom: the electrons orbited the nucleus like planets around the sun. However, this model resulted in an unstable atom. Bohr noted the line spectra of certain elements and assumed the electrons were confined to specific energy states. These were called orbits.

Bohr’s Model of the Hydrogen Atom Each energy level has a quantum number, n. For lowest energy state (ground state): n = 1 The remaining energy states are called excited states: n = 2, n = 3 , n = 4 … For an electron to move from a n = 1 to n = 4 it gains or absorbs energy. For an electron to move from a n = 4 to n = 1 it releases or emits energy in the form of visible light or ultraviolet.

Changing the energy Let’s look at a hydrogen atom

Changing the energy Heat or electricity or light can move the electron up energy levels (“excited”).

Changing the energy As the electron falls back to ground state, it gives the energy back as light.

Changing the energy May fall down in steps Each with a different energy

“Matter Waves” De Broglie summarized the concepts of waves and particles calling the wavelike behavior “matter waves.” As a consequence of de Broglie’s work, we now have techniques such as X-ray diffraction and electron microscopy to study small objects.

Heisenberg’s Uncertainty Principle For atomic particles, we cannot determine the exact position, direction of motion and momentum simultaneously.

Before After Photon changes wavelength Photon Electron Moving Electron Changes velocity Moving Electron