IB DP Chemistry: SL复习笔记2.1.1 The Nuclear Atom

Mass & Charge Distribution

  • The mass of an atom is concentrated in the nucleus, because the nucleus contains the heaviest subatomic particles (the neutrons and protons)
    • The mass of the electron is negligible
  • The nucleus is also positively charged due to the protons
  • Electrons orbit the nucleus of the atom, contributing very little to its overall mass, but creating 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

1.1-Atomic-Structure-Mass-and-Charge-Distribution

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

Types of Subatomic Particles

  • The protonsneutrons 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 is often described as being negligible
  • The relative mass and charge of the subatomic particles are:

Relative Mass & Charge of Subatomic Particles Table

1.1-Atomic-Structure-Table_Subatomic-Particles

Exam Tip

You can see from the table how the relative mass of an electron is almost negligibleThe charge of a single electron is -1.602189 x 10-19  coulombs, whereas the charge of a proton is +1.602189 x 10-19  coulombs. However, relative to each other, their charges are -1 and +1 respectively. This information can also been found in the IB Data Booklet

 

 

 

 

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