Structure and Properties of Organic MoleculesElectrons exhibit wave-particle duality. There are 2 types of wave: travelling (ripples on a pond) standing waves (guitar string). An electron in an atomic orbital can be described like a bound, stationary vibration – a standing wave. Consider a guitar string being plucked in the middle We get a standing wave, which at one moment has all of the string up, and then the next moment, all of the string down. Figure 2-1 An instantaneous picture of the waveform would show the string in a smooth curve either displaced above or below the horizontal rest position. The amplitude of the wave is the square of the displacement. Imagine the amplitude being 3 dimensional – this is the shape of a 1s orbital. An orbital is described by its wave function, ψ, (psi), which is a mathematical description. The electron density at any point is equal to ψ2. (The +ve and –ve signs are notcharges, just phases). A 1s orbital is spherically symmetrical, and is often represented as a circle (meaning a sphere). This corresponds to the Fundamental frequency of the wave / guitar string. If we place our finger exactly half way along the string and pluck again, the string vibrates, we observe a standing wave but the midpoint does not move. Ch02 Structure and Properties 1
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