Atomic Structure
Physics: IB Diploma Higher Level, topic 5.1.2
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 an atom is 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 of Sub-Atomic Particles
The 3 different sub-atomic particles (protons, neutrons and electrons) have different relative charges. Atoms have no overall charge (are neutral). In an atom, these charges all cancel each other out.
Protons (+1)
- Protons have a relative charge of +1.
- 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.
Electrons (-1)
- Electrons have a relative charge of -1.
- 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.
Neutrons (0)
- Neutrons have a relative charge of 0 - they are neutral.
- Like protons, they are found in the nucleus.
Test yourself on Atomic Structure
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?