Atomic Theory
Q: This scientist created the first modern atomic theory in the early 1800s.
A: John Dalton
Q: This subatomic particle carries a positive charge.
A: Proton
Q: Isotopes of the same element differ in the number of these particles.
A: Neutrons
Q: This color of visible light has the highest energy.
A: Violet
Q: When an electron falls from a higher to a lower energy level, it does this.
A: Releases a photon of light (emits energy)
Q: He discovered the electron using cathode ray tubes.
A: J.J. Thomson
Q: The number of protons in an atom is called this.
A: Atomic number
Q. What does it mean when we ask for % abundance?
A. % abundance tells you what percentage of all atoms of an element are a particular isotope
Q: What happens to the wavelength when the frequency of light increases?
A: It decreases (inverse relationship).
Q: Spectral lines differ between elements because of what?
A: Unique electron energy levels
Q: This model of the atom incorrectly described electrons as scattered in a positively charged sphere.
A: The Plum Pudding Model
Q: This value equals the total number of protons and neutrons in an atom.
A: Mass number
Q: Why is the atomic mass on the periodic table rarely a whole number?
A: It is a weighted average of all naturally occurring isotopes.
Q: If red light has a longer wavelength than blue light, which one has greater frequency and energy?
A: Blue light (shorter wavelength → higher frequency and energy)
Q: When white light is viewed through a spectroscope, it produces a continuous spectrum. Explain what a continuous spectrum looks like and why it forms.
A: A continuous spectrum shows an unbroken “rainbow” of all visible wavelengths. It forms because white light contains all wavelengths, and no electrons are absorbing or emitting specific energies to create lines.
Q: He concluded that atoms are mostly empty space with a dense, positively charged nucleus.
A: Ernest Rutherford
Q: How do you calculate the number of neutrons in an atom?
A: Subtract the atomic number from the mass number (Neutrons = Mass number – Atomic number)
Q: Chlorine has two main isotopes: Cl-35 and Cl-37. Explain why the atomic mass on the periodic table is closer to 35 than to 37.
A: Because Cl-35 is more abundant, so it contributes more to the weighted average atomic mass.
Q. In the equation c = λv what do each of the variables represent and what are their units?
c — Speed of Light
What it represents: The speed of light in a vacuum
Units: meters per second (m/s)
Value: 3.00×108 m/s3.00×108m/s
λ — Wavelength
What it represents: The distance between two consecutive crests (or troughs) of a wave
Units: meters (m)
Can also be written in nanometers (nm), micrometers (μm), etc.
v — Frequency
What it represents: The number of wave cycles that pass a point per second
Units: Hertz (Hz)
Equivalent to 1/s or s⁻¹
Q: What is the difference between an absorption spectrum and an emission spectrum?
A:
Absorption spectrum: dark lines appear where light is absorbed.
Emission spectrum: bright lines appear where light is emitted.
Q: This scientist discovered the neutron, explaining why isotopes differ in mass.
A: James Chadwick
Q: Copper has atomic number 29 and mass number of 63.546. How many protons, neutrons, and electrons does Cu²⁺ have?
Protons: 29
Neutrons: ≈ 35 (63.546 ≈ 64 → 64 – 29 = 35)
Electrons: 27 (Cu²⁺ has lost 2 electrons)
Q: An element has two isotopes:
• 70% with mass 35
• 30% with mass 37
Calculate the weighted average atomic mass.
A: (0.70)(35) + (0.30)(37) = 24.5 + 11.1 = 35.6 amu
Q: A green photon has a wavelength of 5.20×10⁻⁷ m. Calculate its frequency.
A.
c = λv
ν=(3.00×10^8 / 5.20×10^−7) ≈ 5.77×10^14 Hz
Q: Describe the full process that creates an emission spectrum (5 steps)
A:
Electrons absorb energy → jump to excited state → fall back to lower energy levels → release photons of specific wavelengths → spectral lines appear.