← Journey Inside the Atom

Lesson 9 of 11

The big picture

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Each new model answered a result the last could not.

Journey Inside the Atom, one line for each idea
Idea	Remember
The piece has parts	Cathode rays are electrons. Every atom has them.
Something with a charge	Electron −1, proton +1. An atom is neutral.
Where the mass sits	A tiny, dense nucleus. Most of an atom is empty space.
A picture that had to change	Dalton, then Thomson, then Rutherford, then Bohr.
Shells	K, L, M hold 2, 8, 18. The outermost shell holds at most 8.
Which atom is it	Z = protons. A = protons + neutrons.
Filling the shells	K takes 2. L takes 8. M takes only 8 in the first 18 elements. The outermost shell holds at most 8.
The outer shell decides	Generally, fewer than 4 outer electrons: lose. More than 4: gain. Exactly 4: share.

Now open Chapter 8, Journey Inside the Atom, in your book. Try its questions with these ideas.