Atomic Structure, Waves, and Electron Configuration: General Chemistry Study Notes

Bohr Model

Introduction to the Bohr Model

The Bohr Model is a foundational concept in atomic theory, describing electrons in atoms as occupying fixed energy levels. It builds upon earlier models and introduces quantized orbits for electrons.

• Planetary Model: The Bohr Model is often called the "planetary model" because it depicts electrons orbiting the nucleus like planets around the sun.

• Comparison to Previous Models: Bohr's Model differs from J.J. Thomson's "plum pudding" model and the Quantum Mechanical Model. Thomson's model did not include a nucleus or quantized energy levels, while the Quantum Mechanical Model uses probability distributions for electron locations.

• Fixed Energy Levels: In the Bohr Model, electrons can only occupy certain energy levels. These are quantized and explain the discrete lines seen in atomic emission spectra.

• Application: Bohr's Model helps explain why atoms emit or absorb light at specific wavelengths.

• Example: The hydrogen atom's emission spectrum shows distinct lines corresponding to electron transitions between energy levels.

Waves

Properties of Waves

Waves are characterized by several properties, including wavelength, frequency, and energy. These properties are essential for understanding electromagnetic radiation and atomic spectra.

• Wavelength (λ): The distance between two consecutive peaks of a wave, typically measured in meters (m).

• Frequency (ν): The number of wave cycles that pass a point per second, measured in hertz (Hz).

• Energy (E): The energy carried by a wave, related to its frequency.

• Units: Wavelength (m), frequency (Hz), energy (Joules).

Relationships Between Wave Properties

The relationship between a wave's frequency and its wavelength is given by the wave equation. Energy is also related to frequency.

• Wave Equation:

  • $c = \lambda \nu$

  • Where $c$ is the speed of light ($3.00 \times 10^8$ m/s), $\lambda$ is wavelength, and $\nu$ is frequency.

• Energy Equation:

  • $E = h \nu$

  • Where $E$ is energy, $h$ is Planck's constant ($6.626 \times 10^{-34}$ J·s), and $\nu$ is frequency.

• Scientific Notation: Calculations often require scientific notation due to the small or large values involved.

Electromagnetic Spectrum (EMS)

The electromagnetic spectrum encompasses all types of electromagnetic radiation, classified by wavelength and frequency.

• EMS Interpretation: To compare energy, frequency, and wavelength, use the relationships above.

• Visible Light Spectrum: Wavelengths in the visible range are typically 400–700 nm.

• Example: Red light has a longer wavelength and lower frequency than blue light.

Ground vs. Excited State

Atomic Energy States

Atoms can exist in different energy states depending on the arrangement of their electrons.

• Ground State: The lowest energy state of an atom, where electrons occupy the lowest available energy levels.

• Excited State: When an atom absorbs energy, electrons move to higher energy levels.

• Electron Transitions: When electrons return to lower energy levels, they release energy as light.

• Example: The emission spectrum of hydrogen results from electrons dropping from excited states to the ground state.

Energy Levels, Sublevels, and Orbitals

Electron Arrangement in Atoms

Electrons are organized into principal quantum levels, sublevels, and orbitals, which determine the chemical properties of elements.

• Principal Quantum Number (N): Indicates the main energy level of an electron.

• Sublevels: Each principal level contains sublevels (s, p, d, f).

• Orbitals: Sublevels are divided into orbitals, each holding up to two electrons.

• Example: The second energy level (N=2) contains s and p sublevels.

Electron Configuration and the Periodic Table

Aufbau Principle and Electron Configuration

The arrangement of electrons in an atom follows specific rules, which can be predicted using the Aufbau Principle and the periodic table.

• Aufbau Principle: Electrons fill the lowest energy orbitals first.

• Aufbau Chart: A diagram that shows the order in which orbitals are filled.

• Electron Configuration: The notation that shows the distribution of electrons among orbitals.

• Periodic Table Blocks: The table is divided into s, p, d, and f blocks, corresponding to the sublevels being filled.

• Application: The location of an element on the periodic table helps predict its electron configuration.

• Example: Carbon: $1s^2 2s^2 2p^2$

Memorization and Practice

Students should be familiar with key equations, metric prefixes, and the Aufbau diagram for electron configurations.

• Key Equations:

  • $v = f \lambda$

  • $E = h \nu$

• Metric Prefixes: nano, micro, milli, giga, mega

• Aufbau Diagram: Shows the order of orbital filling (see chart in materials).

Summary Table: Wave Properties and Relationships

Property	Symbol	Unit	Relationship
Wavelength	λ	meters (m)	$c = \lambda \nu$
Frequency	ν	hertz (Hz)	$c = \lambda \nu$
Energy	E	joules (J)	$E = h \nu$

Additional info:

• Practice worksheets and lab activities (wave, frequency, speed, energy, units, electron configuration, line spectrum) are recommended for mastery.

• Gizmo simulations and Pearson problems provide interactive learning opportunities.