What were Bohr's key modifications to Rutherford's atomic model?

Bohr proposed that electrons are stationary and don't orbit at all Electrons can only exist in specific allowed orbits with fixed energies — they don't emit radiation while in these orbits Bohr showed that electrons orbit in spirals, not circles Bohr proposed that electrons and protons share the same energy level

According to Bohr's model, what happens when an electron moves from a higher energy level to a lower one?

The electron releases thermal energy as heat, not light A photon is emitted with energy equal to the difference between the two energy levels: E = hf The electron splits into two smaller particles The atom gains mass equal to the energy lost by the electron

What is an emission spectrum?

The range of colours produced when white light passes through a prism The specific set of frequencies (colours) of light emitted by an element when its atoms are energised — like a fingerprint for each element The absorption of all colours except one, which is then reflected The spectrum of radiation emitted by any object above absolute zero

Heated hydrogen produces four visible emission lines: violet, blue-green, and two red lines. What does the Bohr model say these lines represent?

Each line corresponds to a different element mixed in with the hydrogen Each line corresponds to electrons falling from a specific higher energy level to level 2 — each transition has a unique energy difference producing a photon of a specific frequency Each line is produced by a different type of photon leaving the hydrogen molecule The lines represent different temperatures of the hydrogen gas

What is the ground state of an atom in Bohr's model?

The state where all electrons are in the outermost orbit The state where the atom has absorbed the maximum possible energy The lowest possible energy level — the state the electron naturally returns to when all excess energy has been emitted The state where the nucleus and electrons are at the same temperature

What is an absorption spectrum, and how does it relate to the emission spectrum of the same element?

An absorption spectrum is the same as an emission spectrum — they look identical When white light passes through a cool gas, atoms absorb photons at the same frequencies they would emit — producing dark lines at exactly the same positions as the emission lines An absorption spectrum shows all possible colours absorbed, leaving a dark image Absorption spectra only occur in liquids — gases only produce emission spectra

Why was the Bohr model a major advance despite being imperfect?

It was not an advance — Rutherford's model was more accurate It introduced the concept of quantised energy levels and successfully predicted hydrogen's spectrum — establishing that quantum rules are necessary for atomic physics It was an advance because it proved electrons don't actually exist It correctly predicted spectra for all elements — not just hydrogen

How does spectroscopy allow astronomers to determine the composition of distant stars?

Astronomers heat star samples in a laboratory and measure the colours they glow Each element has unique spectral lines — dark absorption lines in a star's spectrum identify which elements are in its atmosphere Stars of different colours are made of different elements by definition Astronomers use X-ray telescopes to detect the nuclear composition of stars directly

Why does the Bohr model fail for atoms with more than one electron?

The Bohr model fails because heavy atoms have too many energy levels to calculate It cannot account for electron-electron repulsion — the model only considers the attraction between one electron and the nucleus Multi-electron atoms require relativity, which Bohr didn't include The Bohr model actually works perfectly for all atoms — it was later found to be correct

Bohr's model bridges classical and quantum physics. Which classical idea did he keep, and which did he replace with a quantum rule?

He kept quantum rules and replaced all classical mechanics He kept: electrons orbit the nucleus (classical mechanics). He replaced: electrons can only orbit at specific radii (quantum rule replacing the classical idea that any orbit is possible) He replaced classical gravity with a quantum gravity and kept all other classical ideas Bohr made no use of classical physics — his model was purely quantum