Protons, Neutrons & Electrons (Edexcel GCSE Physics: Combined Science)

Properties of Sub-atomic particles

• The different particles that make up atoms have different properties
• Relative mass is a way of comparing particles. It is measured in atomic mass units (amu)
• A relative mass of 1 is equal to mass of 1.67 × 10^-27 kg
• Charge can be positive or negative
• Relative charge is, again, used to compare particles
• The fundamental charge is equal to the size of the charge on a proton and an electron, however the electron's charge is negative
• The properties of each of the particles are shown in the table below:

Positrons

• A positron is the antiparticle of an electron
• It has the same mass as an electron, and the same size of charge, however it has a positive charge
• Positrons can be produced during nuclear beta-plus decay
  • a proton spontaneously changes into a neutron and a positron

• They only exist in normal conditions for a fraction of a second before they react with electrons and are destroyed

• Although atoms contain particles of different charge, the total charge within an atom is zero
  • This is because the number of electrons is equal to the number of protons

A Lithium atom has three protons, four neutrons and three electrons

• The following table sets out the calculation of the total charge in the Lithium atom:

Total Charge Calculation Table

• If an atom loses electrons, then it is said to be ionised

Step 1: Count the number of protons in the carbon nucleus

• • There are 6 protons in the carbon atom

Step 2: Determine the number of electrons

• • Remember, the number of electrons in an atom is equal to the number of protons
  • Therefore there must be 6 electrons in the carbon atom