The Periodic Table & Periodicity

What this lesson covers

The Periodic Table & Periodicity is a 9-part Class 9 Chemistry lesson. Each part makes one point and then hands over to the next, so it can be read in a sitting or picked up again at the part you stopped on. It defines the idea in plain words before using it, works through an example step by step, breaks the topic into its parts and compares them, names the mistakes that cost marks in an exam, ends with a recap of what to remember.

How it begins

The Periodic Table lists every element in order of atomic number: the number of protons. Mendeleev's insight in 1869 was that if you arrange elements this way, similar properties repeat at regular intervals. That repetition is what periodicity means, and it is why he could leave gaps and correctly predict elements nobody had found yet. We now know why it repeats: the table is really a map of electron arrangement.

The 9 parts

1. A table arranged by structure
2. Groups and periods
3. The groups that matter most
4. Trends across a period
5. Mendeleev's gaps
6. Predicting an element you have never met
7. Where marks get lost
8. What to remember
9. Watch one worked through