In Bohr's model, how is the energy of a hydrogen electron's orbit related to the quantum number n?

Energy = +13.6 eV × n — higher n means higher energy, n=1 has the lowest energy Energy = −13.6 eV / n² — higher n means higher (less negative) energy; n=1 is the ground state with energy −13.6 eV Energy = −13.6 eV × n² — energy increases with the square of n All energy levels are the same — Bohr's model gives equal spacing between levels

What is ionisation energy, and what is hydrogen's ionisation energy according to Bohr?

The energy released when an electron moves from n=2 to n=1 The energy needed to completely remove an electron from its ground state — for hydrogen, this is 13.6 eV The kinetic energy of an electron in the n=1 orbit The energy per mole of hydrogen atoms, equal to 13.6 kJ/mol

An electron in a hydrogen atom falls from n=3 to n=2. What is the energy of the photon emitted?

3.40 eV 1.51 eV 1.89 eV 13.6 eV

What is the Balmer series of spectral lines?

Spectral lines produced when hydrogen electrons fall to the ground state (n=1) Hydrogen emission lines produced when electrons fall from higher levels (n=3, 4, 5, 6…) down to n=2 — four of these lines fall in the visible spectrum Lines in the infrared spectrum produced by electrons falling to n=3 All the spectral lines of hydrogen combined into one series

Why does each element have a unique emission spectrum ('fingerprint')?'

Elements have different sized atoms, so their electrons travel different distances Each element has a unique set of energy levels determined by its atomic number — transitions between these unique levels produce photons of unique frequencies Elements emit different colours because they contain different amounts of Planck's constant The spectrum is random and differs each time you heat the element

Neon signs glow in their characteristic orange-red colour. What produces this colour?

Neon contains orange pigment molecules that fluoresce under electrical excitation Electrons in neon atoms are excited by electrical discharge and emit photons of specific frequencies as they fall back to lower energy levels — neon's energy levels happen to produce orange-red photons Neon glows orange because it is the hottest noble gas Electrical current itself is orange — the neon gas simply makes this visible

Why do atoms only emit or absorb photons of specific frequencies, not a continuous spectrum?

Atoms are very small and can only produce small amounts of each colour Because energy levels are quantised — only photons whose energy exactly equals the difference between two allowed levels can be emitted or absorbed Atoms emit a continuous spectrum but filters in the atmosphere remove certain colours Because atoms only contain a small number of electrons

Hydrogen's n=1→n=2 transition requires absorbing a photon of 10.2 eV. What does this tell us about the minimum photon energy that can excite a ground-state hydrogen atom?

Any photon with energy greater than 1 eV can excite a hydrogen atom Any photon with energy less than 10.2 eV cannot excite a ground-state hydrogen atom — the photon's energy must exactly match an allowed transition Only photons with exactly 13.6 eV can interact with hydrogen Photons of any energy can be absorbed by hydrogen — they just produce different effects

Bohr's model successfully predicted hydrogen's spectrum. Why couldn't it be the final word on atomic structure?

Bohr's model was the final theory — quantum mechanics is just a mathematical reformulation of the same ideas Bohr's model only worked for helium — it failed for hydrogen It only worked for hydrogen; it couldn't predict spectra of multi-electron atoms, line intensities, or the fine structure of spectral lines Bohr's model couldn't explain why hydrogen exists — it predicted all atoms should be hydrogen

Astronomers can determine a star's chemical composition by analysing its spectrum. Which historical discovery made this possible?

Astronomers send robots to collect samples from stars and analyse them on Earth The discovery that each element has a unique emission/absorption spectrum — dark Fraunhofer lines in the Sun's spectrum revealed which elements were present in its atmosphere The discovery that all stars are made of the same element (hydrogen) — so no analysis is needed Astronomers can identify elements by their colour — red stars are iron, blue are nitrogen