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# Energy Levels, Electrons, and the Periodic table

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1. Energy Levels, Electrons, and the Periodic table You NEED to be referring to the periodic table while reading these notes! Get it out! Look at it!

2. Energy levels • 1st energy level can hold 2 electrons • 2nd energy level can hold 8 electrons • 3rd energy level can hold 18 electrons • 4th – 7th energy levels can hold 32 electrons

3. Octet Rule • The valance energy level (the outermost energy level) can only hold 8 electrons. • When the 3rd – 7th energy levels are NOT the valance, they can hold more than 8. • For example, when the 4th energy level is the valance, the 3rd can now hold 18.

4. Periodic Table • The row number of the element tells you WHAT ENERGY LEVEL IS VALANCE. • The row number does NOT always tell you what energy level each atom is currently putting electrons in.

5. 1st Row • Represent the 1st energy level, which can only hold two electrons. • Hydrogen is putting the first electron in the 1st energy level. • Helium is putting the 2nd electron in the 1st energy level. • The 1st energy level is FULL with Helium.

6. 2nd Row • Represents the 2nd energy level, which can hold 8 electrons. • Lithium is putting the 1st electron in the 2nd energy level. Beryllium is putting the 2nd electron in the 2nd energy level. Boron is putting the 3rd electron in the 2nd energy level.. Ect.. To Neon, which is putting the 8th electron in the 2nd energy level. • The 2nd energy level is FULL with Neon.

7. 3rd Row • Represents the 3rd energy level as valance – but does not FILL the 3rd energy level, because the 3rd energy level can hold 18 electrons, but only 8 elements are on the 3rd row. • Sodium is putting the 1st electron on the 3rd energy level. Magnesium is putting the 2nd electron on the 3rd energy level… ect. To Argon, which is putting the 8th electron on the 3rd energy level. • At Argon, no more electrons can go on the 3rd energy level at this time because it is currently the valance.

8. 4th Row • Represents that the 4th energy level is valance. • Potassium is putting the 1st electron on the 4th energy level; Calcium is putting the 2nd electron on the 4th energy level (*4th energy level is now valance). • Scandium is putting the 9th electron on the 3rd energy level (since the 3rd is no longer the valance at this point, it can now hold 18 electrons.) Titanium is putting the 10th electron on the 3rd energy level.. Ect… to Zinc, which is putting the 18th electron on the 3rd energy level. At this point, the 3rd energy level is now FULL.

9. 4th Row (cont) • Gallium goes back to putting electrons on the 4th energy level, so it puts the 3rd electron on the 4th energy level…. To Krypton, which puts the 8th electron on the 4th energy level. At this point, the 4th energy level is the valance, so even though it can hold 32 electrons, no more electrons can be on the 4th energy level at this time. • The 4th energy level will not be full until the 6th row!

10. 5th Row • Represents that the 5th energy level is valance. • Rubidium is putting the 1st electron on the 5th energy level; Strontium is putting the 2nd electron on the 5th energy level (*5th energy level is now valance). • Yttrium is putting the 9th electron on the 4th energy level (since the 4th is no longer the valance at this point, it can now hold more than 8 electrons.) Zirconium is putting the 10th electron on the 4th energy level.. Ect… to Cadmium, which is putting the 18th electron on the 4th energy level. At this point, the 4th energy level is NOT yet full, but the next electron will not go on the 4th energy level at this time (too crowded).

11. 5th Row (cont) • Indium goes back to putting electrons on the 5th energy level, so it puts the 3rd electron on the 5th energy level…. To Xenon, which puts the 8th electron on the 5th energy level. At this point, the 5th energy level is the valance, so even though it can hold 32 electrons, no more electrons can be on the 5th energy level at this time. • The 5th energy level will not be full until the 7th row!

12. 6th Row • Represents that the 6th energy level is valance. • Cesium is putting the 1st electron on the 6th energy level; Barium is putting the 2nd electron on the 6th energy level (*6th energy level is now valance). • Remember that the 4th energy level did not fill back on the 5th row. (It only went to 18 electrons with Cadmium). At this point, electrons will go back to finish filling the 4th energy level, starting with the 19th electron. • Lanthanum puts the 19th electron on the 4th energy level. Cerium puts the 20th electron on the 4th energy level…ect, to Ytterbium which puts the 32nd and final electron on the 4th energy level (which is now full).

13. 6th Row (cont) • Beginning with Lutetium, electrons will now return to filling the 5th energy, so Lutetium puts the 9th electron on the 5th energy level (since the 5th is no longer the valance at this point, it can now hold more than 8 electrons.) Hafnium puts the 10th electron on the 5th energy level.. Ect… to Mercury,, which is putting the 18th electron on the 5th energy level. At this point, the 5th energy level is NOT yet full, but the next electron will not go on the 5th energy level at this time (too crowded). • Thallium goes back to putting electrons on the 6th energy level, so it puts the 3rd electron on the 6th energy level…. To Radon, which puts the 8th electron on the 6th energy level. At this point, the 6th energy level is the valance, so even though it can hold 32 electrons, no more electrons can be on the 6th energy level at this time.

14. 6th Row (cont) • The 6th energy does not finish filling (it’s impossible because the atoms are too unstable to have that many protons to balance the electrons necessary to fill the 6th energy level).

15. 7th Row • Represents that the 7th energy level is valance. • Francium is putting the 1st electron on the 7th energy level; Radium is putting the 2nd electron on the 7th energy level (*7th energy level is now valance). • Remember that the 5th energy level did not fill back on the 6th row. (It only went to 18 electrons with Mercury). At this point, electrons will go back to finish filling the 5th energy level, starting with the 19th electron. • Actinium puts the 19th electron on the 5th energy level. Thorium puts the 20th electron on the 5th energy level…ect, to Nobelium which puts the 32nd and final electron on the 5th energy level (which is now full).

16. 7th Row (cont) • Beginning with Lawrencium, electrons will now return to filling the 6th energy, so Lawrencium puts the 9th electron on the 6th energy level (since the 6th is no longer the valance at this point, it can now hold more than 8 electrons.) Rutherfordium puts the 10th electron on the 6th energy level.. Ect… but it doesn’t go to 18 (as far as we know) because the atoms become too unstable. • The 7th energy level does not have electrons in the 3rd – 8th Positions (atoms would be too unstable.) • The 7th energy level does not finish filling (again, atoms would become too large/unstable.)

17. If you are still confused… • Go back and read all the notes again.. WITH YOUR PERIODIC TABLE. Each time the name of an element is mentioned, find that element, then read what electron and energy level it is filling. • You have to go back and forth between the notes and the periodic table for this to make any kind of sense!