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IGCSEPhysics: Co-ordinated Sciences (Double Award)CIERevision Notes5. Nuclear PhysicsThe NucleusProtons, Neutrons & Electrons

Protons, Neutrons & Electrons (CIE IGCSE Physics: Co-ordinated Sciences (Double Award))

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Ann H

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Ann H

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Relative charge

  • Charge can be positive or negative
  • Protons, neutrons and electrons have different properties and different charges
    • Protons have a positive charge
    • Electrons have a negative charge
    • Neutrons have no charge
  • Relative charge can be used to compare these properties
    • Relative charge is the ratio of the charge of a particle compared to the fundamental charge 
    • Because relative charge is a ratio, it has no units
  • Fundamental charge is equal to the magnitude of the charge on a proton and an electron = 1.6 × 10−19 C
  • The relative charge of a proton is 

proton space equals space fraction numerator 1.6 cross times 10 to the power of negative 19 end exponent space straight C over denominator 1.6 cross times 10 to the power of negative 19 end exponent space straight C end fraction space equals space plus 1

  • The relative charge of an electron is

electron space equals space fraction numerator negative 1.6 cross times 10 to the power of negative 19 end exponent space straight C over denominator 1.6 cross times 10 to the power of negative 19 end exponent space straight C end fraction space equals space minus 1

  • The relative charge of a neutron is

neutron space equals space fraction numerator 0 space straight C over denominator 1.6 cross times 10 to the power of negative 19 end exponent space straight C end fraction space equals space 0

Table of relative charges

Particle Relative charge
Proton +1
Neutron 0
Electron −1

Examiner Tip

You don't need to know how to calculate relative charge, but you do need to understand what it is. You do also need to remember what the relative charges are for each subatomic particle.

Nuclear charge

Extended tier only

  • Nuclear charge is the relative charge of the nucleus
  • This is determined by the proton number of the atom
  • Relative charge is calculated by: 

nuclear space charge space equals space number space of space protons space in space the space nucleus space cross times space relative space charge space of space straight a space proton

  • An element of carbon has a proton number of 6
    • So the relative charge of carbon is 6 × (+1) = 6

Worked example

What is the relative charge of the chromium nucleus Cr presubscript 24 presuperscript 52 ? 

 

Answer:

Step 1: Determine the number of protons

  • The number of protons is the proton number
  • This is the Z number in the AZX notation

straight X presubscript straight Z presuperscript straight A

 

    • This chromium nucleus has 24 protons

Cr presubscript 24 presuperscript 52

Step 2: State the relative mass of 1 proton 

  • 1 proton has a relative charge of +1

Step 3: Multiply relative charge of 1 proton by the number of protons

  • This nucleus of chromium therefore has a relative charge of +24

Examiner Tip

Charge can be either positive (+) or negative (–). Usually, when a number is positive, we don't write the + sign, but when dealing with relative charge, we do.

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    Ann H

    Author: Ann H

    Expertise: Physics

    Ann obtained her Maths and Physics degree from the University of Bath before completing her PGCE in Science and Maths teaching. She spent ten years teaching Maths and Physics to wonderful students from all around the world whilst living in China, Ethiopia and Nepal. Now based in beautiful Devon she is thrilled to be creating awesome Physics resources to make Physics more accessible and understandable for all students no matter their schooling or background.