Nuclear Model of the Atom (SL IB Chemistry)

What are subatomic particles?

• The protons, neutrons and electrons that an atom is made up of are called subatomic particles
• These subatomic particles are so small that it is not practical to measure their masses and charges using conventional units (such as grams or coulombs)
• Instead, their masses and charges are compared to each other, and so are called ‘relative atomic masses’ and ‘relative atomic charges’
• These are not actual charges and masses, but rather charges and masses of particles relative to each other
  • Protons and neutrons have a very similar mass, so each is assigned a relative mass of 1
  • Electrons are 1836 times smaller than a proton and neutron, and so their mass can be considered negligible
• The relative mass and charge of the subatomic particles are:

Relative Mass & Charge of Subatomic Particles Table

Subatomic particle	Relative charge	Relative mass
Proton	+1	1
Neutron	0	1
Electron	–1	negligible

Where are the subatomic particles located?

• Atoms contain a positively charged, dense nucleus
  • The nucleus is positively charged due to the protons
  • The nucleus is dense because mass of an atom is concentrated in the nucleus, which contains the heaviest subatomic particles
  • The subatomic particles in the nucleus can generally be called nucleons, although they are specifically the neutrons and protons
• Negatively charged electrons occupy the space outside the nucleus
  • They can be described as orbiting the nucleus where they create a 'cloud' of negative charge
• The electrostatic attraction between the positive nucleus and negatively charged electrons orbiting around it is what holds an atom together

Atomic Structure Diagram

The mass of the atom is concentrated in the positively charged nucleus which is attracted to the negatively charged electrons orbiting around it