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Introduction to Chemistry: Electrons in Atoms and the Periodic Table

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  • Why was the Hindenburg airship filled with hydrogen gas?
    Hydrogen gas was used for buoyancy because it is less dense than air, but it is highly reactive and flammable.
  • What makes helium gas inert compared to hydrogen?
    Helium has a highly stable electron configuration with two protons and two electrons, resulting in a full outer shell that makes it inert.
  • What does Mendeleev's periodic law state?
    When elements are arranged by increasing atomic mass, certain sets of properties recur periodically.
  • What is the speed of light (c)?
    Light travels through space at a constant speed of 3.0 x 10\(8\) m/s.
  • What is wavelength (λ) in terms of light waves?
    Wavelength is the distance between adjacent wave crests.
  • How many colors does white light split into when passed through a prism?
    White light splits into 7 colors: red, orange, yellow, green, blue, indigo, and violet.
  • Which visible light color has the longest wavelength and which has the shortest?
    Red has the longest wavelength (~750 nm) and violet has the shortest (~400 nm).
  • What is frequency (ν) of a wave?
    Frequency is the number of wave crests passing a point per second.
  • How are wavelength and frequency related?
    They are inversely related: shorter wavelength means higher frequency and greater energy.
  • What part of the electromagnetic spectrum has the highest energy?
    Gamma rays have the highest energy.
  • What part of the electromagnetic spectrum has the lowest energy?
    Radio waves have the lowest energy.
  • What is the nature of light according to quantum mechanics?
    Light has both wave and particle nature; particles of light are called photons.
  • What is an emission spectrum?
    An emission spectrum shows specific wavelengths of light emitted by energized atoms.
  • What did Bohr's atomic model propose about electron orbits?
    Electrons travel in fixed, quantized circular orbits around the nucleus.
  • What happens when an electron jumps from a higher to a lower energy orbit in Bohr's model?
    A photon of light is emitted.
  • Why was the Bohr model replaced by the quantum-mechanical model?
    Bohr's model could not explain emission spectra of multi-electron atoms and lacked a full description of electron behavior.
  • What do quantum-mechanical orbitals represent?
    Orbitals represent probability maps showing where an electron is likely to be found, not exact paths.
  • What does the principal quantum number (n) describe?
    It describes the size and energy level of an orbital; higher n means larger size and higher energy.
  • What does the angular quantum number (l) describe?
    It describes the shape of the orbital (spherical, dumbbell, cloverleaf, etc.).
  • What is the Pauli exclusion principle?
    An orbital can hold a maximum of two electrons with opposite spins.
  • What is Hund's rule?
    Electrons occupy orbitals of the same energy singly first, with parallel spins, before pairing.
  • How many valence electrons does sulfur have in the configuration 1s²2s²2p⁶3s²3p⁴?
    Sulfur has 6 valence electrons and 10 core electrons.
  • What is the general valence shell electron configuration of alkali metals (Group 1A)?
    ns¹, and they tend to lose one electron to form +1 cations.
  • What is the general valence shell electron configuration of halogens (Group 7A)?
    ns²np⁵, and they tend to gain one electron to form -1 anions.
  • Why are noble gases generally inert?
    They have filled s and p orbitals with 8 valence electrons (except helium), resulting in stable electron configurations.