Matter and Reactions
Atoms & the Periodic Table
12 min · 2 worked examplesFree
What an atom is made of, why the periodic table is arranged as it is, and why that arrangement predicts behaviour.
After this lesson you can
- Say what decides which element an atom is
- Work out an electron configuration from the shells
- Read a group number off the table and predict how the element behaves
Protons, neutrons, electrons
An atom is a dense nucleus of protons and neutrons surrounded by electrons. The proton is positive, the electron negative and equal in charge, the neutron neutral.
The number of protons, the atomic number, decides which element it is. Six protons is carbon, always. Change it and you have changed the element, which is nuclear physics rather than chemistry.
Neutrons can vary without changing the element, giving isotopes: carbon-12 and carbon-14 are both carbon, with different masses and different stability. Electrons can be gained or lost, giving ions, and since electrons carry the charge, an atom that loses one becomes positive.
Almost all of chemistry is electrons. The nucleus sets the identity and then takes no further part.
In the full lesson
- Protons, neutrons, electrons
- Shells and why the table has that shape
- Reading the table
Free with an account. Read it, work the examples, answer the questions, then build it in the simulator.