Atoms, Ions and Molecules Chemistry of Life Atoms, Ions and Molecules

Atoms

The Atom Every element is made of atoms All atoms of any element are the same Atoms of different elements are different

Protons

Neutrons

Electrons

Atomic Number – Atomic Mass Protons in Nucleus Atomic Mass: Sum of Masses of Protons + Neutrons (e.g., 207.2 g/mol)

Periodic Pattern

Thomson Model: The Electron J.J. Thomson discovered electrons using an experimental device similar to your TV---over 100 years ago! He deduced the electrons must be from atoms, and there must be other, more massive particles in the atom.

Rutherford’s Atom Model Mostly empty space Small dense region-nucleus Protons are part of nucleus Hypothesized a third, neutral particle existed Neutron discovered later by Chadwick

Bohr’s Atom & Quantum Mechanics

Quantum Model Today, “the quantum model is the most realistic vision of the overall structure of the atom. It explains much of what we know about chemistry and physics” including why elements are ordered by atomic number in the Periodic Table.

See the Atom Photo courtesy National Institute of Standards and Technology (NIST) STM image (7 nm x 7 nm) of a single zigzag chain of cesium atoms (red) on a gallium-arsenside surface (blue) Photo courtesy NIST Photo source: IBM's Almaden Research Labs Atoms can be positioned on a surface using the STM tip, creating a custom pattern on the surface.

Fun Facts