2. Define the number of electrons on the outer shell of the atoms in the following elements:
- a) 13 Al 2e 8e …
- b) 17 Cl 2e 8e …
- c) 20 Ca 2e 8e 8e …
3. Look at the periodic table. How many electron shells are there in:
- a) the 7 th element
- b) the 10 th element
- c) the 16 th element
- d) the 20 th element
4. Which elements have the following electron configurations?
- a) 1s 2 2s 1
- b) 1s 2 2s 2
- c)1s 2 2s 2 2p 3
- d) 1s 2 2s 2 2p 6

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