Atomic Theory and Models Quiz

Atomic Theory Timeline

• 440 BCE, Democritus: Matter is composed of indivisible particles called atoms. In Greek, "atom" means "indivisible."

Laws of Chemistry

• 1782, Lavoisier (France): The law of conservation of mass: Mass cannot be created or destroyed, it is merely rearranged.

• 1799, Proust (France): The law of definite proportions: A chemical compound always contains exactly the same proportion of elements by mass.

Dalton's Atomic Theory (1803)

• 1803, Dalton (England): Matter is composed of extremely small particles called atoms.
• An element consists of atoms of the same type only.
• Different atoms combine in simple whole-number ratios to form compounds.
• In a chemical reaction, atoms are separated, combined, or rearranged, but never destroyed.

Development of the Atomic Model

• 1897, Thomson (England): Identified the electron. The electron has a negative charge. Plum-pudding model.

• 1909, Rutherford (New Zealand): Discovered the atomic nucleus and the proton, which has a positive charge. Bombarded a thin gold foil with alpha particles and observed that some particles were deflected, which led to the conclusion that atoms have a nucleus and mostly empty space.

• 1913, Bohr (Denmark): Published a theory of atomic structure relating the arrangement of electrons in an atom in fixed orbits around the nucleus, similar to planets orbiting the sun. Assigned a quantum number (energy level) to each orbit.

• 1926, Schrödinger (Austria): Developed the quantum mechanical model. Electrons occupy orbitals around the nucleus. Introduced the electron cloud model.

• 1927, Heisenberg (Germany): Developed the uncertainty principle, stating that the position and trajectory of an electron cannot both be known with perfect accuracy simultaneously.

• 1932, Chadwick (England): Proved the existence of neutrons. Determined that the atomic number is determined by the number of protons in the nucleus of the atom.

Subatomic Particles

• Atom: Smallest particle of an element that retains the properties of the element.

• Proton: Positively charged particle located in the atom's nucleus.

• Neutron: Neutrally charged particle located in the atom's nucleus.

• Electron: Negatively charged particle located around the nucleus in orbitals.

Atomic Structure

• Atomic Number: The number of protons in an atom, which identifies the element.

• Mass Number: The sum of protons and neutrons in an atom.

• Isotopes: Atoms of the same element with different numbers of neutrons and different masses.

• Atomic Weight: The weighted average of the masses of all isotopes of that element found in nature.

Periodic Table

• Groups: Elements in the same group have the same number of valence electrons (the electrons in the outermost shell). Group number determines the number of valence electrons.

• Periods: Elements in the same period (horizontal row) have the same number of energy levels (electron shells). Period number determines the shell or energy level.

Electron Configuration and Orbitals

• Electron Configuration: Arrangement of electrons in different energy levels and sublevels.

• Sublevels/Subshells: s, p, d, f sublevels exist within energy levels. Each sublevel has a specific maximum number of electrons (s=2, p=6, d=10, f=14).

• Orbitals: Regions in space with a high probability of finding an electron.

Quantum Numbers

• Principal Quantum Number (n): Describes the electron's energy level and distance from the nucleus.
• Angular Momentum Quantum Number (l): Describes the shape of the orbital (s, p, d, f).
• Magnetic Quantum Number (ml): Describes the orientation of the orbital in space.
• Spin Quantum Number (ms): Describes the spin of the electron (clockwise or counterclockwise).

Chemical Bonds

• Ionic Bond: Formed by the transfer of electrons between a metal and a nonmetal.

• Covalent Bond: Formed by the sharing of electrons between two nonmetals.

• Ion: An atom that has lost or gained electrons, resulting in a net positive (cation) or negative (anion) charge