Chem 101L: Spectroscopy

What is electromagnetic radiation?

Energy consisting of oscillating electric and magnetic fields moving at the speed of light.

What is amplitude?

The height of a wave from the midline to its maximum displacement.

What is wavelength (λ)?

The distance between two consecutive peaks or troughs of a wave.

What is frequency (ν)?

The number of wave cycles that pass a point per second.

Relationship between wavelength and frequency?

c=λν

What does the symbol c represent?

The speed of light (3.00 × 10⁸ m/s).

How are wavelength and frequency related?

Inversely — as wavelength increases, frequency decreases.

Formula for photon energy?

E=hν

What is Planck’s constant (h)?

6.63 × 10⁻³⁴ J·s.

Combined energy–wavelength relationship?

E=hc/λ

What happens when an electron relaxes to a lower energy level?

It emits a photon whose energy equals the energy difference of the transition.

General wavelength range of visible light?

400–750 nm.

Which color has the shortest wavelength?

Violet (~400 nm).

Which color has the longest wavelength?

Red (~750 nm).

What determines an electron’s energy level?

Distance from nucleus, nuclear charge, electron shielding, orbital type, and surroundings.

What must happen for an electron to move to a higher energy level?

It must absorb energy.

What must happen for an electron to move to a lower energy level?

It releases a photon.

What is ΔE in electron transitions?

The difference between final and initial energy levels:
ΔE=Efinal−Einitial

Allowed energy levels in the Bohr model?

En​=−(13.6 eV​/n²)

What is the ground state of hydrogen?

n=1

What is the Rydberg equation for hydrogen emission lines?

1/λ​=R(1/n_f²−1/n_i²)

Value of the Rydberg constant (R)?

1.097 × 10⁷ m⁻¹.

Condition for photon emission using quantum numbers?

ni​>nf​

What is the Balmer series?

Visible-light transitions ending at nf=2nf​=2 in hydrogen.

What is a line emission spectrum?

Discrete wavelengths emitted from specific electron transitions; unique to each element.

What is a continuous spectrum?

A full rainbow of wavelengths; no discrete lines (e.g., sunlight, hot metals).

Why does each element have a unique spectrum?

Each element has unique electron energy levels and allowed transitions.

What are common sources of line spectra?

Gas discharge tubes, flames, heated elements.

What is spectroscopy?

Analysis of light emitted or absorbed to determine electronic structure or identity of elements.

What is a spectroscope?

Device that splits light into component wavelengths using a diffraction grating.

What is a diffraction grating?

A surface with closely spaced grooves that separates light via constructive interference.

What does a spectroscope measure?

Wavelengths of emitted light (qualitative/intuitive, not intensity).

What is a spectrophotometer?

A quantitative instrument that measures intensity of light vs wavelength.

Why is calibration required?

To relate instrument readings (e.g., ruler positions, detector values) to actual wavelengths.

What is a calibration curve?

A graph relating instrument response (x-axis) to a known physical property (y-axis).

Why are known mercury lamp wavelengths used in calibration?

They are well-established standards for accurate wavelength assignment.

What does the R² value in a calibration curve indicate?

How well the line fits the data (closeness to 1 = good fit).

Why do different metals produce different flame colors?

Each metal has unique electron transitions → unique emitted wavelengths.

What does a flame test qualitatively identify?

Metal ions based on emission line colors.

Why is a spectroscope better than the naked eye for flame tests?

The eye blends colors; a spectroscope isolates precise wavelengths.

What must be true for an emitted photon to be visible?

Its energy must correspond to wavelengths between 400–750 nm.

How does energy relate to wavelength?

Short wavelength → high energy
Long wavelength → low energy

What are photons?

Packets (quanta) of light energy.

Relationship between energy change and emitted photon?

ΔEelectron​=Ephoton​=hν