Proton or Atomic Number

PlantUML Diagram

3.3 Proton or Atomic Number

Identity of an Element

Proton Number (Atomic Number)

  • Symbol: Z
  • Refers to the number of protons in the nucleus
  • Determines the identity of an element
  • Equal to the number of electrons in a neutral atom

Uniqueness of Proton Number

  • Each element has a unique proton number
  • Determines:
    • Element'sproperties
    • Position in the periodic table

Examples:

  • Carbon: 6 protons
  • Sodium: 11 protons
  • Nitrogen: 7 protons
  • Oxygen: 8 protons

Nucleon Number (Mass Number)

  • Total number of protons and neutrons in an atom
  • Calculation: No. of neutrons = mass number - atomic number
  • Isotopes: Atoms of an element with different numbers of neutrons

Example 3.1: Determining Protons and Neutrons

Given:
Atomic number = 17
Mass number = 35

Solution:
Number of protons = atomic number = 17
Number of neutrons = mass number - atomic number = 35 - 17 = 18

Radioactivity

  • Occurs in elements with unbalanced nuclear forces
  • Radioactive decay: Process of nucleus decay to become another atom
  • Effects on atomic identity:
    • Neutron emission: Changes to another isotope of the same element
    • Proton emission: Changes to a different element

Examples:

  • Carbon-14 decay to Nitrogen-14
  • Uranium-238 decay to Lead-206