Atomic Numbers and Structures

Discovery of the Electron: J.J. Thomson used a cathode ray tube to find negatively charged particles. 

Electron discovery led to the conclusion positive particles must exist to balance electrons in atoms. Also atoms must contain heavier particles accounting for more of the mass. Also concluded all elements contain identically charged electrons. 

Atomic Number: Shows protons and electrons.

• Changing proton numbers would create new element

• Changing electrons creates ions, changing charges on elements

  • Anion - Elements with negative charge, gained electrons. 

  • Cation - Elements with positive charge, lost electrons.

AMU: Atomic Mass Units are used to measure the mass of particles like electrons, protons, and neutrons.

Atomic Mass Number: Number of protons and neutrons combined, averaged between isotopes, versions of elements with different numbers of neutrons

• Found with a weighted average. (Mass isotope) x (Abundance of isotope) + (Mass isotope) x (Abundance of isotope)