1. Chapter 4 Section 2: Organizing the elements (Have your book handy)
Key concepts: How did Mendeleev discover the pattern that led to the periodic table?
What information about elements does the periodic table provide?
How are elements created?
Key terms: atomic mass, periodic table, period, group, chemical symbol, nuclear fusion

2. Russian scientist, Dmitri Mendeleev
Mendeleev thought that the elements must form some kind of pattern
To find it, he wrote each element’s melting point, density, and color. He also included atomic mass and the number of chemical bonds it could form.
Atomic mass is the average mass of all the isotopes of an element.
Mendeleev noticed that a pattern of properties appeared when he arranged the elements in order of increasing atomic mass. (this is what you should know)

3. Smart enough to grow a cool beard.

5. Mendeleev’s periodic table
Wasn’t perfect. By strictly using atomic mass, he did not always have elements that reacted similarly together. He figured that was wrong.
In 1869, he published the first periodic table. Yay. It wasn’t that great. Boo. You don’t need to memorize it. Yayy. It looked like this:

8. The Modern Periodic Table
In the periodic table used today, the properties of elements repeat in each period – or row – of the table.
An important change – in 1913, Henry Moseley discovered a way to measure the positive charge on an atom’s nucleus. This measured the atomic number, which is the number of protons in the nucleus. As a result, a few of the elements shifted position and some patterns of properties became more regular.

10. Reading an element’s square
The periodic table has one square for each element. In the book, each square includes the element’s atomic number, chemical symbol, name, and atomic mass.

12. Open your books to page 112-113
Take a look at the periodic table.
How many elements are there? (note, some are not officially confirmed)
What characteristic determines an element’s place in the periodic table?

13. Practice What is the atomic mass of Sc? What is its name?
What is the atomic number of F? what is its name? how many protons does it have?
What is the atomic number of P? what is its name?

14. Organization of the periodic table
Periods: horizontal rows. On the left side of the table are highly reactive metals. Less reactive metals are in the middle. Then come the metalloids, followed by nonmetals on the right. The pattern is repeated in each period.

15. Groups Groups – 18 vertical columns
Consist of elements with similar characteristics. For example, group 1 are metals that react violently with water, while the elements in group 2 react with water slowly or not at all.

16. Huh???
So, be able to identify periods (horizontal rows) and groups (vertical columns) on a periodic table. BOOM. Easy.

17. BTW Lady Gaga is a huge fan of the periodic table.
It’s how she writes her music

18. Please note: the chemical symbol for radon is actually Rn, not Ro

19. Average atomic mass
Most elements consist of a mixture of isotopes (remember isotopes? If you just blanked out, you don’t remember what isotopes are. They are atoms of the same element with different numbers of neutrons and the same number of protons), so the average atomic mass is determined from the combined percentages of the isotopes.

20. How elements form
When colliding nuclei have enough energy, they can join together. They have to smash together fast enough.
Nuclear fusion is a process in which two atomic nuclei combine forming a larger nucleus and releasing huge amounts of energy. Nuclear fusion occurs in stars on a huge scale and results in heavier elements (up to Iron)

21. But waaaait (not on the test)
Wait wait, where do other elements come from?
The Big Bang theory states that at the time of the Big Bang, only Hydrogen, Helium, and Lithium existed.
Those elements then smashed together within stars (fusion, or stellar nucleosynthesis) to form bigger elements (up to Iron)

22. BUT WAAAIT (not on ze test)
What about elements heavier than Iron?
Oh, no big deal, those get formed in supernovae. When the supernova explodes, large numbers of neutrons are shot out of the interior of the star at high velocities. Think of these like pellets in a shot gun shell that has been fired.
These neutrons pass through the outer regions of the star, colliding with the atoms already there (mostly hydrogen). The collisions happen very rapidly and quickly build up very large atoms.

23. What DO I NEEEEED TO KNOWWW??
Know about average atomic mass
Know what you can read from an element’s square
Know how elements form in nuclear fusion. (YES AWESOME I KNOW ABOUT FUSION)
Know how the periodic table is organized (periods, groups, atomic number)