2.3 Electron Arrangement Atomic Emission Spectra &

Atomic Emission The “light” emitted from atoms and ions Light = the electromagnetic radiation Visible light we know is only one small portion of this spectrum Useful to prove electronic structure of atoms & that electrons are in certain allowed energy levels

ColourVioletBlueGreenYellowOrangeRed Wavelength(nm) (nm = 1x10 -9 m) White Light Spectrum

Atoms can be excited causing electrons to change energy levels. Each element has its own characteristic line spectrum used to identify it based on the colours visible in atomic absorption spectroscopy.

Moving Electrons: Releasing Photons Gas is placed in a glass tube & an electric current is passed through the tube to move the electrons by changing their energy. As the electrons change energy levels, energy is released of differing amounts – this energy is released as light and is called a photon. Different energies mean different frequencies and wavelengths of light is emitted resulting in different spectrums. Paschen Seried: Electrons move from higher energy livel to the third energy level (IR spectrum) Balmer Series: Electrons move from a higher energy level to the second energy level (visible spectrum). Lyman Series: Electrons move from a higher energy level to the first energy level (UV spectrum).

Hydrogen Spectrum

Light Equations Energy & Light Frequency E = hν E = energy emitted (kJ) h = constant (3.99 x kJ∙s /mol) ν = frequency (Hz or sec -1 ) **Direct relationship** Lower E = Lower Frequency **Given the energy emitted by a photon, you can find the frequency of the light.** Light Wavelength & Frequency λ = c/ν λ = wavelength (m) c = speed of light (3 x 10 8 m/s) ν = frequency (Hz or sec -1 ) **Indirect Relationship** Higher frequency = Smaller wavelength **Given the frequency already found, you can determine wavelength of light & therefore spectrum type or colour.

Balmer Equation This equation can be used to find energy emitted by electrons moving to the 2 nd energy level. These lights fall in the visible spectrum as different colours. Higher energy level # Negative if moving high to low; positive if low to high level.

Lyman Equation Used to determine the energy emitted by an electron going to the first energy level. These lights fall into the UV spectrum and we cannot see them. Negative if moving high to low; positive if low to high level. Higher energy level #

Practice Problems: 1. An electron moves from the 5 th energy level to the second energy level in the hydrogen atom. a.What is the energy associated with this transition? b.What line in the series will appear as the result of this transition? c.What is the wavelength associated with this energy?

2. a. Determine the energy released as a hydrogen electron moves from the 7 th energy level to the 3 rd energy level. b. Which line in the series would this transition produce? c. Determine the frequency and wavelength associated with this energy. Would we see it?