2. Chemical Symbols in the Periodic Table

3. How is the Periodic Table Arranged?
Alphabetically from A to Z
By atomic mass, from small to large
By number of protons, starting with 1
Randomly
In the order the elements were discovered

4. Periodic table is arranged by number of protons!
This is also by Atomic Number
By coincidence, the elements are generally in order of increasing atomic mass, but not always…..

5. For example…. Cobalt has 27 protons, mass = 58.9 amu
Next after Co comes Nickel
Nickel has 28 protons , but mass = 58.7 amu (less mass than cobalt)

6. Periods Periods are the horizontal rows. There are 7 periods 1 2 3 4 56 7
(6)
(7)

7. Groups or Families
Groups (also called families) are the vertical columns. There are 18 groups. 1 18

8. Most elements are metals

9. Non-metals live in upper right corner (except Hydrogen)

10. 6 Metalloids live near the red stair: B, Si, Ge, As, Sb, TeX

11. Group 1 metals are called alkali metals

12. Group 2 metals are called alkaline earth metals

13. Transition Metals are in groups 3 through 12 They tend to form colorful ions and compounds

14. Halogens are in group 17 Noble gases in group 18

15. 7 elements are DIATOMIC

16. Allotropes
Elements that can exist in different forms in the same phase are allotropes:
O2 (oxygen gas) and O3 (ozone) are allotropes
Allotropes have different chemical and physical properties

17. Valence Electrons Definition: all the electrons in an atom’s
HIGHEST ENERGY LEVEL

18. Valence Electrons Remember: There are seven energy levels
Energy Level 1 can hold two e- in S orbital
Energy Level 2 can hold two e- in S, 6 in P
Energy Level 3 : S, P, D
Energy Level 4-7: S, P, D, F

19. However….
Since according to the aufbau principle d and f orbitals fill after the S and P orbitals in the next highest energy level,
Valence electrons are always in S or P orbitals
(2 in S) + (6 in P) = 8 (max) Valence e-

20. How to determine which e- are valence e- :
Step 1: Write out the electron configuration for the atom
11Na = 1S2 2S2 2P6 3S1
Step 2: Count how many e- in the highest energy level:
Energy level 3 = highest, so there is 1 valence e-
Level 3 is highest

21. The good news:
It is easy to determine valence e- simply by looking at the periodic table:
Group 1 has 1 valence e-
Group 2 has 2
Group 13 has 3
Group 14 has 4
Group 15 has 5…….. Group 18 has 8

22. What about the transition metals?
For now, assume that they have 2.
But sometimes they can also have 1, or 3 or more

23. Write out the e- configuration for the following elements, then check and see what Group they are in:
12Mg 8O
17Cl
18Kr
26Fe
19K