Models of the Atom
Which experiment disproved the plum pudding model?
Rutherford's model
Give the full electronic configuration for a neutral sulfur atom.
1s² 2s² 2p⁶ 3s² 3p⁴
What causes the lines in the emission spectrum of hydrogen?
Electron transitions between quantized energy levels
Define isotope.
Atoms with the same number of protons but different numbers of neutrons
Who proposed that atoms combine in simple whole-number ratios to form compounds?
John Dalton
Which subatomic particle's discovery required the modification of Dalton's atomic theory?
Electron
Which orbital is filled last in a scandium atom?
3d
Which series in the hydrogen spectrum lies in the visible range?
Balmer series
Why do isotopes have nearly identical chemical properties?
Because they have the same number and arrangement of electrons
Why did the discovery of the neutron improve the nuclear model?
Because it explained isotopes and missing mass in the nucleus
How did Bohr’s model explain the stability of atoms which classical physics could not?
Quantization of angular momentum and fixed energy levels that prevent electrons from spiraling into the nucleus
Why does chromium have an irregular electron configuration?
Because the half-filled 3d⁵ and 4s¹ orbitals provide greater stability
Why do spectral lines converge at higher frequencies?
Because energy levels get closer together at higher n-values (converge at ionization)
How does the existence of isotopes affect atomic mass?
It makes the atomic mass a weighted average based on isotopic abundance.
What is a major limitation of Bohr’s model in describing atoms beyond hydrogen?
It cannot accurately predict spectra due to electron-electron interactions
Why does Schrödinger’s model replace Bohr’s in modern quantum theory?
Because it incorporates the wave nature of electrons and provides probability distributions rather than fixed orbits
How many unpaired electrons are in an Fe²⁺ ion?
4
Calculate the wavelength of light emitted when an electron falls from n=4 to n=2
Approximately 486 nm
A sample contains 25% ²⁵Mg, 10% ²⁶Mg, and 65% ²⁴Mg. Calculate the relative atomic mass.
Approximately 24.4
Describe a modern technology that uses electron transitions in atoms.
Atomic absorption spectroscopy (or lasers, or MRI)
Explain how the failure of classical physics to describe atomic emission spectra led to the development of quantum mechanics.
It is because classical physics predicted a continuous spectrum, but only discrete lines were observed, prompting the need for quantized energy levels and wavefunctions
What are the quantum numbers for the highest energy electron in a bromine atom?
n = 4, l = 1, mₗ = +1, 0, or −1, mₛ = ±½
Why are hydrogen-like spectra not observed in multi-electron atoms?
Due to electron-electron repulsion and sublevel splitting (shielding effects)
How is mass spectrometry used to distinguish between isotopes?
By separating ions based on mass-to-charge ratio using a magnetic field
A synthetic element has isotopes with half-lives of milliseconds. What challenges does this present for studying its electronic structure, and how might scientists overcome them?
Short half-lives prevent detailed spectroscopic analysis, so scientists use computational models, predicted trends, and decay product studies to infer electronic structure