Atomic Structure
Inside the Atom
To describe the structure of an atom and explain why nearly all its mass is found in the nucleus.
What you will learn
What protons, neutrons and electrons are
Where the particles are found inside an atom
The charge and relative mass of each particle
Why atoms have no overall electrical charge
Why almost all an atom’s mass is in its nucleus
Explanation
An atom has a small nucleus containing positive protons and neutral neutrons, surrounded by negative electrons. Protons and neutrons each have relative mass about 1; electrons have a much smaller mass. Most atomic mass is in the nucleus, and most atomic volume is empty space; a neutral atom has equal proton and electron numbers. Example: Describe a neutral atom with six protons. It has six electrons; its neutron number cannot be determined from proton number alone. Use evidence. Apply the model.