Chem 2.2/2.3

What is a wave?

A repeating oscillation that transfers energy through space.

What is wavelength, λ?

The distance between consecutive peaks or troughs; measured in meters (m).

What is frequency, ν?

The number of wave cycles passing a point per second; measured in hertz (Hz) or s⁻¹.

What is amplitude?

The height of a wave from its midpoint to a peak or trough.

What does amplitude determine for light?

Intensity or brightness.

What is the SI unit of frequency?

Hertz (Hz), equivalent to s⁻¹.

What is the wave-speed equation?

v = λν

What equation applies to electromagnetic radiation in vacuum?

c = λν

What is the speed of light?

c = 3.00 × 10⁸ m/s (approximately).

How are wavelength and frequency related?

They are inversely related: as wavelength increases, frequency decreases.

What is a photon?

A discrete packet of electromagnetic energy.

What is Planck's constant?

h = 6.626 × 10⁻³⁴ J·s.

What is the photon-energy equation?

E = hν

What is photon energy in terms of wavelength?

E = hc/λ

How does photon energy change with frequency?

Higher frequency means higher photon energy.

How does photon energy change with wavelength?

Longer wavelength means lower photon energy.

What is the visible-light wavelength range?

Approximately 400–700 nm.

Which visible color has the longest wavelength?

Red.

Which visible color has the shortest wavelength?

Violet.

Which visible color has the highest frequency?

Violet.

Which visible color has the lowest photon energy?

Red.

What is the electromagnetic spectrum order?

Radio → microwave → infrared → visible → ultraviolet → X-ray → gamma.

Which electromagnetic radiation has the highest energy?

Gamma rays.

Which electromagnetic radiation has the lowest energy?

Radio waves.

What does nm mean?

Nanometer = 10⁻⁹ m.

What does pm mean?

Picometer = 10⁻¹² m.

What does μm mean?

Micrometer = 10⁻⁶ m.

What does mm mean?

Millimeter = 10⁻³ m.

What does cm mean?

Centimeter = 10⁻² m.

What does k mean as an SI prefix?

Kilo = 10³.

How do you convert nm to m?

Multiply by 10⁻⁹ m/nm.

How do you convert pm to m?

Multiply by 10⁻¹² m/pm.

How do you convert μm to m?

Multiply by 10⁻⁶ m/μm.

How do you find wavelength from frequency?

Use λ = c/ν. Make sure units are consistent.

How do you find frequency from wavelength?

Use ν = c/λ. Convert wavelength to meters if c is in m/s.

How do you find photon energy from wavelength?

Use E = hc/λ. Convert wavelength to meters first.

How do you find photon energy from frequency?

Use E = hν.

What does shorter wavelength mean?

Higher frequency and higher photon energy.

What does longer wavelength mean?

Lower frequency and lower photon energy.

What is constructive interference?

When wave peaks align in phase and amplitudes add, producing a larger amplitude/brighter light.

What is destructive interference?

When a peak overlaps a trough and amplitudes cancel partly or completely.

What is diffraction?

The spreading/bending of waves when they pass through an opening or around an obstacle.

What does the double-slit experiment demonstrate?

Its interference pattern provides evidence that light behaves as a wave.

What is wave-particle duality?

Light exhibits both wave-like and particle-like properties.

What phenomenon demonstrates the particle nature of light?

The photoelectric effect.

What is the photoelectric effect?

The ejection of electrons from a metal surface when illuminated with light above the metal's threshold frequency.

What is threshold frequency?

The minimum frequency of light needed to eject electrons from a particular metal.

What happens below the threshold frequency?

No electrons are ejected, regardless of light intensity.

What happens when intensity increases above the threshold?

The number of emitted electrons increases.

What determines the kinetic energy of photoelectrons?

The frequency of the incoming light, because frequency determines photon energy.

Does increasing brightness increase the kinetic energy of each photoelectron?

No. Above threshold, increased brightness mainly increases the number of electrons emitted.

What is binding energy?

The minimum energy required to remove an electron; in the chapter it is also called threshold/ionization energy in this context.

What is a continuous spectrum?

A continuous range of wavelengths without gaps.

What is a line spectrum?

A spectrum containing discrete lines at specific wavelengths.

Why does each element have a unique line spectrum?

Each element has its own allowed/quantized electron energy levels, so its transitions have characteristic photon energies.

What does quantized mean?

Only specific discrete energy values are allowed, rather than a continuous range.

What is the ground state?

The lowest possible energy state of an atom.

What is an excited state?

A state with energy greater than the ground-state energy.

What happens during atomic absorption?

An electron absorbs a photon and moves to a higher energy level.

What happens during atomic emission?

An electron moves from a higher energy level to a lower energy level and releases a photon.

Absorption or emission: electron moves UP?

Absorption.

Absorption or emission: electron moves DOWN?

Emission.

What is Bohr's key idea for hydrogen?

Hydrogen electrons occupy specific, quantized energy levels and exchange energy when moving between them.

What is hydrogen's Bohr energy equation?

Eₙ = −(2.178 × 10⁻¹⁸ J)/n²

What does n represent?

The principal energy level.

What happens to hydrogen energy as n increases?

Energy increases and becomes less negative; the electron is farther from the nucleus.

Which hydrogen level has the lowest energy?

n = 1, the ground state.

What is the energy at n = ∞?

E = 0; the electron is no longer bound to the atom (ionized).

What is the equation for atomic energy change?

ΔE = E_f − E_i

What sign is ΔE for absorption?

Positive, because the atom gains energy.

What sign is ΔE for emission?

Negative, because the atom loses energy.

Is photon energy ever negative?

No. Photon energy is E_photon = |ΔE|.

What is the Lyman series?

Hydrogen transitions ending at n = 1; ultraviolet.

What is the Balmer series?

Hydrogen transitions ending at n = 2; visible light.

What is the Paschen series?

Hydrogen transitions ending at n = 3; infrared.

What is the Brackett series?

Hydrogen transitions ending at n = 4; infrared.

What is the Pfund series?

Hydrogen transitions ending at n = 5; infrared.

What visible hydrogen wavelengths are listed in the chapter?

Approximately 656, 486, 434, and 410 nm.

What is an absorption spectrum?

A spectrum with dark lines where specific wavelengths were absorbed as electrons moved to higher energy levels.

What is an emission spectrum?

A spectrum with bright lines from photons emitted as electrons moved to lower energy levels.

How are absorption and emission spectra related?

Their characteristic lines occur at the same wavelengths; absorption appears as dark lines and emission as bright lines.

Why do atomic spectra provide evidence for quantized energy?

Only specific photon energies/wavelengths are emitted or absorbed, producing discrete spectral lines.

How do you solve a wavelength-from-frequency problem?

1) Identify ν. 2) Use λ = c/ν. 3) Keep units consistent. 4) Report the requested unit.

How do you solve a frequency-from-wavelength problem?

1) Convert λ to meters if needed. 2) Use ν = c/λ. 3) Check that units reduce to s⁻¹/Hz.

How do you solve a photon-energy-from-wavelength problem?

1) Convert λ to meters. 2) Use E = hc/λ. 3) Report energy in joules per photon.

How do you solve a hydrogen transition problem?

1) Identify n_i and n_f. 2) Calculate E_i and E_f using Eₙ. 3) Calculate ΔE = E_f − E_i. 4) Use |ΔE| for photon energy.

How do you find wavelength from a hydrogen transition energy?

First find E_photon = |ΔE|, then use λ = hc/E_photon.

What should you check before using c = λν?

Make sure units are consistent; with c in m/s, wavelength should be in meters.

What should you check before using E = hc/λ?

Convert wavelength to meters and use h in J·s.

What is the key relationship among wavelength, frequency, and photon energy?

Shorter λ → higher ν → higher E; longer λ → lower ν → lower E.

What is the key difference between intensity and frequency for light?

Intensity/brightness relates to the amount/number of photons; frequency determines the energy of each photon.