Protons & neutrons
- Protons and neutrons are not fundamental particles
- They are each made up of three quarks
- Protons are made up of two up quarks and a down quark
- Neutrons are made up of two down quarks and an up quark
Composition of protons & neutrons
Protons and neutrons are made up of three quarks
- You will be expected to remember these quark combinations for exam questions
Worked example
State how many 'up' quarks there are in the nucleus of iron, .
Answer:
Step 1: Calculate number of protons
- The number of protons is from the proton number = 26 protons
Step 2: Calculate number of neutrons
- The number of neutrons = nucleon number - proton number = 56 - 26 = 30 neutrons
Step 3: Up quarks in a proton
- Protons are made up of uud quarks = 2 up quarks
Step 4: Up quarks in a neutron
- Neutrons are made up of udd quarks = 1 up quark
Step 5: Total number of up quarks
- 26 protons x 2 up quarks = 52 up quarks
- 30 neutrons x 1 up quark = 30 up quarks
- 52 + 30 = 82 up quarks