CHM 2103 Atomic Structure Flashcards
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40 Terms
What is an atom?
The smallest indivisible particle of an element and the basic building block of chemistry.
Who first proposed the atomic theory?
John Dalton in 1803.
When did scientists realize particles smaller than atoms existed?
At the end of the 19th century.
What was the first subatomic particle discovered?
The electron.
How were electrons first discovered?
As cathode rays in discharge tubes.
Why were they called cathode rays?
Because they came from the cathode and caused a glow at the anode end.
What showed that cathode rays carried a negative charge?
They were deflected toward the positive plate in an electric field.
What happens when atoms are excited?
They absorb energy and their electrons move to higher energy levels.
What happens when excited electrons return to lower levels?
They emit light and other electromagnetic energy.
What device splits emitted light into its component wavelengths?
A spectroscope.
What is a line emission spectrum?
A pattern of light produced when electrons drop from high to low energy levels.
What is a line absorption spectrum?
A pattern formed when atoms absorb energy and electrons jump to higher levels.
How does each element's line spectrum appear?
Unique and specific to the element.
What equation relates to hydrogen's spectral lines?
v = cR (1/n₁² - 1/n₂²)
In the formula v = cR (1/n₁² - 1/n₂²), what do n₁ and n₂ represent?
Principal quantum numbers, with n₂ > n₁.
What series results from electrons falling to n₁ = 1?
Lyman series (ultraviolet region).
What series results from electrons falling to n₁ = 2?
Balmer series (visible region).
What series results from electrons falling to n₁ = 3?
Paschen series (infrared region).
What are the n₁ values for the Brackett and Pfund series?
Brackett: n₁ = 4, Pfund: n₁ = 5 (infrared region).
Who proposed that electrons occupy fixed energy levels?
Niels Bohr in 1913.
What do Bohr's energy levels represent?
Fixed orbits of increasing radius around the nucleus.
What happens when an electron absorbs energy?
It moves to a higher energy level (excitation).
What happens when it emits energy?
It drops to a lower energy level (relaxation).
What equation relates energy change to frequency?
ΔE = hv (Einstein-Planck equation)
What is the ground state of an electron?
The lowest energy level it normally occupies.
What causes the line spectrum of hydrogen?
Electrons dropping from excited states to lower energy levels.
What is ionisation energy?
The minimum energy needed to remove an electron from a gaseous atom to infinity.
What is the equation for ionisation?
A(g) → A⁺(g) + e⁻
What does ionisation energy indicate in a line spectrum?
The continuum — when the electron is removed from the atom entirely.
What did Max Planck and Albert Einstein propose about light?
That it behaves as both a particle and a wave — called quantum theory of radiation.
What two phenomena support light's wave nature?
Interference and diffraction.
What is wave-particle duality?
The idea that particles like electrons also behave like waves.
Who introduced the idea of wave-particle duality for electrons?
Louis de Broglie in 1924.
What is the de Broglie relationship?
λ = h/mv
In λ = h/mv, what does each symbol represent?
λ = wavelength, h = Planck's constant, m = mass, v = velocity.
What does momentum equal in classical mechanics?
Mass × velocity
What is Heisenberg's Uncertainty Principle?
It is impossible to know both the exact position and momentum of an electron at the same time.
What is the uncertainty equation?
Δx·Δp ≥ h/2π
What does ψ² represent in quantum mechanics?
The probability of finding an electron at a given point in space.
What is ψ in quantum mechanics?
The wave function that describes the behavior of an electron wave.