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The Wave-Mechanical Model of the Atom A.K.A. The Modern Model

Bright Line Spectra Light is a form of energy. Using a prism, light can be broken into different colors. Different colors of light have different amounts of energy. A full spectrum of light has many different amounts of energy or colors.

Bright Line Spectra When the light given off by gas in a cathode ray tube is examined through a prism, it is not a full spectrum. Instead, there are just bright lines. This means some energies of light are missing. Neon Mercury Hydrogen

Each element has a unique spectrum, which explains why each has a different flame test. But why do they give off light at all? And why are parts of the spectrum missing?

Explaining Bright Line Spectra Electrons pick up energy from the surroundings, and move faster. This makes them move farther from the nucleus. The excited electrons are unstable. They fall back toward the nucleus, giving off energy as light.

Definitions Ground State Excited State When all electrons are in the lowest possible energy levels in an atom Excited State When one or more electrons have absorbed energy and moved to a higher energy level. This creates the potential for that electron to fall back to its original energy level.

Explaining Bright Line Spectra Explain Bright Line Spectra in terms of ground and excited states: An electron absorbs energy and moves from ground state to an excited state The excited state is unstable The electron falls back to ground state releasing energy in the form of light Different colors are caused by electrons falling different distances between energy levels, releasing different amounts of energy.

Bohr’s Explanation Gaps Niels Bohr explained the frequencies of light and the gaps in the hydrogen spectrum. Bohr said the energy of the electron is quantized. Like a person going down stairs, an electron can only be stable in certain positions − not in between. That’s why falling electrons only give off certain frequencies or colors of light. Gaps

Problem with Bohr The Bohr model accounts for the line spectrum of hydrogen perfectly. But… as soon as an element has more than one electron Bohr’s model can’t explain the elements bright line spectrum. A new model must be formed

The Wave-Mechanical Model The Wave-Mechanical model explains the bright line spectra for all elements. The electron moves freely around the nucleus. They move in regions of most probable electron location called orbitals. Cloud of electrons

Evolution of the atom