Electron Arrangement Senior Chemistry R. Slider

Electromagnetic (EM) Spectrum Wavelength The actual length of one full wave. Notice: IR > vis > UV Wavelength The actual length of one full wave. Notice: IR > vis > UV Frequency The number of waves passing a particular point every second. Notice: IR < vis < UV Frequency The number of waves passing a particular point every second. Notice: IR < vis < UV LowerEnergyhigher Relationships The shorter the wavelength, the greater the frequency and the greater the energy Relationships The shorter the wavelength, the greater the frequency and the greater the energy Infrared (IR) Lower energy and higher wavelength than visible light Infrared (IR) Lower energy and higher wavelength than visible light Ultraviolet (UV) Higher energy and lower wavelength than visible light Ultraviolet (UV) Higher energy and lower wavelength than visible light Visible The range of wavelengths/frequencies that we can see with our eyes Visible The range of wavelengths/frequencies that we can see with our eyes

Continuous vs. Line Spectra Continuous Spectra Passing a light source through a prism produces a continuous spectrum of colours where all wavelengths are seen Line Spectra (2 types) Specific to the substance, this spectrum is produced through the excitation of electrons from the ground state to higher energy levels. Emission Emission – once excited, the electrons fall back to ground state and emit particular wavelengths of light that correspond to specific energy transitions Absorption Absorption – particular substance will also absorb the same wavelengths that were emitted in the emission spectra.

Electron transitions of hydrogen Some of the possible e- transitions and their energy levels. The Balmer series show the only visible transitions. The Lyman and Paschen series are also shown. This shows the emission spectrum of hydrogen which can be seen using a spectrometer. The UV and IR regions which we cannot see are also represented.

Line spectra to identify elements Each element will have slightly different energy levels and so will be produce a slightly different line spectrum which acts like a kind of “fingerprint” for that element. Therefore, this can be used to determine the makeup of distant stars

Electron arrangements Recall from the introduction of the atom, we discussed the arrangement of electrons (shown in red above). Because there are more electrons as the atomic number increases, the line spectra become increasingly more complex.

Flame tests Because elements emit particular wavelengths of light, they will produce visible colours if these wavelengths are in the visible region of the Electromagnetic Spectrum If metal salts like the ones on the left are put into a Bunsen flame, they will produce colours that can be used in their identifications. These are known as flame tests, which can be used to qualitatively identify the presence of a particular metal in a solution or a solid salt. This is the basis for Atomic Absorption Spectroscopy (see next slide)

Atomic Absorption Spectroscopy