# Hydrogen Spectra

#### Nutcase

Why is the spectra measured in cm-1 and called wavenumbers?

I read that to make the wavelength I need to do 1/cm, so this makes a logarithm - is the whole point to make a logarithm because the value is so small and for some reason my example is in cm rather than in something smaller?

#### Nutcase

if Balmer series can represent Hydrogen spectra why does this go to n=2? surely Hydrogens ground state should be n=1? I understand that Balmer is specific to ground state 2 but how does it fit with Hydrogen?

Regards

#### chemistrystudy

Recall the frequency (ν) indicates the number of waves passing a given point per second and is expresses as cycles per second. Wavenumber (⊽) on the other hand stands for the number of waves connected in unit length that is per centimeter (cm⁻¹) or per meter (m⁻¹). Thus wavenumber is cm⁻¹.

Transition to the n = 2 level from n = 3, n = 4, n = 5, etc exited states constitute the Balmer series in the visible spectral region. The wavelength of these spectral lines can be calculated by the following equation.

⊽ = 1/λ = R[(1/n₁²) - (1/n₂²)]
n₁ = 2 and n₂ = 3, 4, 5, ...

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