1. Periodic Table, Atomic Number & Isotopes
Why We Use What We Do
Periodic Table, Atomic Number & Isotopes

2. The Periodic Table Mid 1800’s 60 Different Elements were identified
5 were gases at room temperature (all non-metals)
H, O, N, F, Cl
2 were liquids
Hg (metal)
Br (non-metal)
The rest were solids

3. The Periodic Table Construction of The Periodic Table
Elements with similar properties were placed near one another.
Dimitri Mendeleev
In 1869 he published a periodic table

4. Mendeleev’s Periodic Table

6. The Periodic Table Mendeleev’s Table arranged by
Atomic Weight (Molar Mass)
Combining Capacity
Chemical Properties
NaCl vs CuCl2
Modern Periodic Table arranged by
Atomic Number
Number of valence electrons
Supports Combining Capacity Properties

7. The Periodic Table Atomic Number
Determined by the number of Protons in the nucleus
Positive Particles (p+)
Each element has its own atomic number
Na = 11 protons (p+)
Identify every atoms as a particular element by this number.

8. Molar Mass

9. The Periodic Table Mass Number Mass # = (p+) + (n0)
Does not include (e-)
(e-) too small to contribute to the overall mass of the atom.
Mass number changes when the number of neutrons change.

11. The Periodic Table Isotopes:
Atoms with the same number of (p+) but a different number of (n0).
Atoms of the same element with different mass #’s
14C = Radioactive
12C = Non-radioactive
For Example Hydrogen (H with one (p+) but no (n0) ) and Deuterium (H with one (p+) and one (n0) ).
ttp://web.visionlearning.com/custom/chemistry/animations/CHE1.3-an-isotopes.shtml

12. The Periodic Table
Why use Atomic Number rather than Molar Mass (atomic weight)?
Organization by Molar Mass (atomic weight) works well for small atomic weights but not large ones.
Due to many varieties of isotopes

13. The Periodic Table Vertical arrangement
Elements with similar properties were placed in vertical Groups (columns) or Families.

14. Group
Molar Mass

15. Molar Mass
Group

16. Molar Mass
Group

17. Molar Mass
Group

18. Molar Mass
Group
Etc.

19. The Periodic Table Horizontal arrangement
Placed by increasing atomic weights in rows called Periods.

20. Molar Mass
Periods

21. Periods
Molar Mass

22. Periods
Molar Mass

23. Molar Mass
Periods

24. Molar Mass
Periods
Etc.

25. Families/Groups Alkali Metals
Group 1 – Lithium, Sodium, Potassium, Rubidium, Cesium, Francium
1 electron in valence (outer) shell
Very, VERY reactive – not found free in nature
Alkali Metal Clip

26. Family/Group Alkaline Earth Metals
Group 2 – Beryllium, Magnesium, Calcium, Strontium, Barium, Radium
2 electron in valence shell
Very reactive – not usually found pure in nature

27. Families/Groups Nobel Gases
Group 18 – Helium, Neon, Argon, Krypton, Xenon, Radon
Full valence electron shell
Very stable (not reactive)
Under normal conditions do not form compounds with other elements
XeF4 (xenon tetrafluoride) is the first reported stable compound of a noble gas

28. Families/Groups Halogens
Group 17 – Fluorine, Chlorine, Bromine, Iodine, Astatine
7 electrons in valence shell
Halogen means “salt former”
Compounds they form are called salts

29. Families/Groups Transition Metals Groups 3 to 12, periods 4 to 7
1, 2, or 3 electrons in valence electron shell
Hard and have a high melting point
Often used to form alloys (mixtures of metals)