Subatomic Particles

The atom is composed of even smaller particles, called subatomic particles. These are the what give each atom its unique characteristics. Subatomic particles are to atoms what nitrogenous bases are to DNA. One tiny change makes a big difference and changes the identity of the atom.

The number of subatomic particles, protons, neutrons, and electrons, are unique to each atom. The table below summarizes characteristics of each subatomic particle.


There is a shorthand notation to write an element and signify the # of subatomic particles it contains.


#p= atomic number
#n= atomic mass – atomic number
#e= same as #p (in a neutral atom)

Protons: Affect charge AND mass. Typically remain unchanged. They are the identity of the atom/element.

Neutrons: Only affect mass. They can change in number, which then changes mass. Elements with the same #p but different #n (and thus different atomic mass) are called isotopes.

Electrons: Only affect charge and can vary in #. Therefore, if an atom has a + or – charge, it is due to a variation in #e NOT #p because #p does not change.

  • If you have more electrons than protons → – charge
  • If you have less electrons than protons → + charge

Charged particles are called ions. Cations are positively charged and anions are negatively charged.

Example: Try completing the tables below by recording the correct # of subatomic particles. Answers are in blue.



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