Chemistry Atomic Model Overview

Atomic Theory Through the Ages

• Democritus proposed that the universe was made of invisible units called atoms.

  -400 BC

  -took 2000 years to be proved right

• Aristotle supported Democritus's theory about atoms.

• Dalton's Atomic Theory proposed that all matter is made up of atoms, which are indivisible and indestructible particles.

• "billiard ball model" was proposed by john dalton in 1804

• john dalton (1766-1844)

  -wrote the first atomic theory

  -atoms can neither be destroyed nor be created

  -atoms of an element are identical

• J.J. Thomson discovered the electron, a negatively charged particle, which he proposed were embedded in a positively charged sphere.

  -also used cathode ray experiment to discover the existence of the electron

• discovery of the electron

  -1897, Thomson used a cathode ray tube to deduce the presence of a electron.

• nuclear model - Ernest Rutherford's gold foil experiment concluded that atoms have a small, dense, positively charged nucleus at their center.

• Niels Bohr proposed that electrons orbit the nucleus in specific energy levels or shells.

  -According to Bohr's model, electrons can jump between levels with energy being absorbed or emitted.

  -electrons revolve the nucleus (like planets in the solar system)

• Erwin Schrödinger improved upon Bohr's findings by proposing the Quantum Mechanical Model.

  - The Quantum Mechanical Model describes electrons as existing in probability regions called orbitals, a more sophisticated model than Bohr's.

  - Principal Quantum Number (n) refers to the energy level of an electron, with higher numbers indicating higher energy levels.

  -The azimuthal quantum number (ℓ) can take on any integer value from 0 to n-1, with ℓ = 0, 1, 2, and 3 representing s, p, d, and f orbitals, respectively.

  - Each orbital can hold a maximum of two electrons.

Quantum Numbers: Describing Electron Behavior

• The four quantum numbers used to describe electrons in an atom are:
  • Principal Quantum Number (n): Describes the energy level of an electron
  • Azimuthal Quantum Number (ℓ): Describes the shape of an electron's orbital.
  • Magnetic Quantum Number (mℓ): Describes the orientation of an electron's orbital in space.
  • Spin Quantum Number (ms): Describes the spin of an electron, either spin up (+1/2) or spin down (-1/2)

Orbital Types and Configurations

• The letters s, p, d, and f also represent the type of orbitals and correspond to the quantum number ℓ values of 0, 1, 2, and 3, respectively.
• The 3d orbital has 6 available orbitals.
• The maximum number of electrons that can occupy the 2p subshell is 6.
• The orbital notation for oxygen is 1s2 2s2 2p4.
• The Magnetic Quantum Number (mℓ) indicates the orientation of the orbital in space.
• The letters s, p, d, and f stand for sharp, principal, diffuse, and fundamental, respectively, which are historical terms related to the appearance of spectral lines.

Electron Arrangement

• The total number of orbitals found in the 3rd energy level is 9.
• The value of ms for an electron in the 1s orbital if it is spinning clockwise is +1/2.
• Thomson used a cathode ray tube to discover the electron.
• Rutherford concluded that atoms are mostly empty space and have a dense nucleus.
• Rutherford identified the proton as being located in the nucleus.
• Electrons orbit the nucleus similar to how planets orbit the Sun.
• One of Rutherford's conclusions based on the Gold Foil Experiment was that atoms have a positively charged center.

Energy Levels and Quantum Mechanics

• Bohr's model states that electrons can only exist at certain fixed energy levels.
• The term for the amount of energy required to move an electron from one energy level to another is ionization energy.
• The quantum mechanical model describes electrons as existing as probability waves within orbitals, rather than fixed orbits.
• Allowed energies of an electron are determined by its principal quantum number (n) and the potential energy of the electron within the atom's electric field.
• Each energy sublevel corresponds to one or more orbitals of different shapes.
• Orbitals are probability regions where electrons are likely to be found, providing a more realistic representation of electrons' behavior.
• Quantum is the amount of minimum energy an electron can absorb/release to transition between energy levels.

Orbital Shape and Quantum Numbers

• The allowed energies of an electron can be described by its principal quantum number (n).
• The p subshell has a dumbbell shape.
• The value of the magnetic quantum number (mℓ) when ℓ equals 2 is -2, -1, 0, 1, 2.
• The value of the spin quantum number (ms) can be either +1/2 or -1/2.
• The s orbital corresponds to the angular momentum quantum number ℓ = 0.
• s, p, d, and f subshells correspond to ℓ values of 0, 1, 2, and 3, respectively.
• Pauli Exclusion Principle states that no two electrons in the same atom can have identical quantum numbers.