Atomic Model
Physics: AQA A Level, topic 2.1.1
Atomic Model - Example
An atom has a small, positively-charged nucleus surrounded by orbiting negatively-charged electrons.
Hydrogen atom
Size of Atoms vs Nucleus
Atoms have a radius of about 1 × 10-10 metres. However, the nucleus of atoms are even smaller.
Atoms
- If an atom was the size of Wembley Stadium, then...
Nucleus
- ...its nucleus would be the size of a garden pea!
The Charges and Masses of Sub-Atomic Particles
The 3 different sub-atomic particles (protons, neutrons and electrons) have different relative charges and masses. Atoms have no overall charge (are neutral). In an atom, these charges all cancel each other out.
Protons
- Protons have a relative charge of +1.
- In SI units, this is +1.60 × 10-19C.
- They are found in the nucleus.
- An element’s atomic number is the number of protons it possesses.
- All atoms of the same element have the same number of protons.
- Protons have a relative atomic mass of 1.
- In SI units, this is 1.67 × 10-27kg.
Electrons
- Electrons have a relative charge of -1.
- In SI units, this is -1.60 × 10-19C.
- They are found in fixed orbits around the nucleus.
- In any atom, the total number of negative electrons equals the number of positive protons, meaning atoms have no overall electric charge.
- Electrons have a relative atomic mass of 1/2000.
- In SI units, this is 9.11 × 10-31kg.
Neutrons
- Neutrons have a relative charge of 0 - they are neutral.
- Like protons, they are found in the nucleus.
- Neutrons have a relative atomic mass of 1 (the same as a proton).
Test yourself on Atomic Model
What is the charge of an atom's nucleus?
Which of the following statements are true of atoms?
What do we call a small, positively charged particle in an atom's nucleus?
What do we call a small, negatively charged particle that orbits an atom's nucleus?
In what environment would the relative mass of an atom change?