1. Organizing the Elements
1. Dmitri Mendeleev organized the elements by increasing atomic mass.
2. Mendeleev left spaces in his periodic table and he was able to predict new elements based on chemical properties.
Is the periodic table still organized by increasing atomic mass?

3. Organizing the Elements
1. Periodic table - elements are arranged by increasing atomic number and by changes in physical and chemical properties.
2. Henry G.J. Moseley led to the arrangement of elements based on their increasing atomic numbers.

4. Parts of the Periodic Table
1. Groups (or families) - vertical columns in the periodic table numbered 1-18.
Elements in each group have similar properties.
2. Periods - horizontal rows of elements on the periodic table.
The elements increase by one proton and one electron as you go from left to right in a period.

6. Electron Cloud Structure
Electrons within the electron cloud have different amounts of energy.
The closer the energy levels are to the nucleus the less energy that they have.

8. Energy Levels: # of Electrons
Energy level 1  2 electrons
Energy level 2  8 electrons
Energy level 3  18 electrons
Energy level 4  32 electrons
When an energy level is full of electrons, the next energy level begins to fill up with electrons until it has reached its limit.

9. Valence Electrons
1. Elements in the same group have the same number of valence electrons (electrons in the outer energy level).
2. Valence electrons determine chemical properties.
3. Maximum number of valence electrons is in the noble gases (group 18)… they have 8 and are very stable.

10. Draw the electron cloud structure (showing energy levels) for:
Boron
2. Oxygen
3. Lithium
4. Chlorine
5. Nitrogen
6. Neon
7. Magnesium
8. Silicon

11. P = 5
N = 6
Boron:
Atomic # = 5
Atomic mass = 11

12. Boron
P = 8
N =

13. Oxygen

14. Boron
Oxygen

15. Boron
Oxygen

16. Boron
4. Chlorine
5. Nitrogen
6. Neon
7. Magnesium
8. Silicon

17. Boron
4. Chlorine
5. Nitrogen
6. Neon
7. Magnesium
8. Silicon

18. Boron
2. Oxygen
3. Lithium
4. Chlorine
5. Nitrogen
6. Neon
7. Magnesium
8. Silicon

19. Rows on the Periodic Table
An element’s period number (row number) indicates the number of occupied energy levels.
Example: All elements in period 3 have three occupied energy levels. 1 2 3

20. Period or Row 1 on the Periodic Table: How many energy levels?

21. Period or Row 2 on the Periodic Table: How many energy levels?

22. Last Vertical Row on the Periodic Table: Stable
The last element in each period ends with a full outer energy level and is therefore VERY stable!

23. Valence Electrons Group 1  1 valence electron
Group 2  2 valence electrons
Group 13  3 valence electrons
Group 14  4 valence electrons
Group 15  5 valence electrons
Group 16  6 valence electrons
Group 17  7 valence electrons
Group 18  8 valence electrons (except He)
Skip groups 3-12 (transition elements) because they can vary.

24. Electron (Lewis) Dot Diagrams
Outer electrons are so important in determining the chemical properties of an element… this is a special way to represent them.
It uses:
1. the chemical symbol
2. dots to represent the valence electrons (electrons in outer energy level)

25. Examples:
Fluorine
Carbon
Sulfur
Magnesium

26. Same Group = Similar Properties
Example 1: Group 1:Alkali metals
shiny, malleable (can be hammered into thin sheets) and ductile (can be pulled into wires)
Example 2: All group 17 elements have seven electrons in their outer energy levels

27. Same Group = Similar Properties
Example 3: Group 18 elements already have a full stable outer energy level of 8 valence electrons; that is why they do not react readily with other elements.

28. Review Questions
How are the elements arranged in the periodic table?

29. Review Questions How are the elements arranged in the periodic table?
Increasing atomic number and by changes in physical and chemical properties.

30. Review Questions
What do the elements in a vertical column of the periodic table have in common?

31. Review Questions
What do the elements in a vertical column of the periodic table have in common?
elements in the same group have similar properties because they have the same number of valence electrons

32. Review Questions
What do the dots in this electron dot diagram represent?

33. Review Questions
What do the dots in this electron dot diagram represent?
valence electrons

34. Review Questions
What is the maximum number of electrons that can fill the first and second energy levels?

35. Review Questions
What is the maximum number of electrons that can fill the first and second energy levels?
first energy level  2
second energy level  8

36. Review Questions
The horizontal rows of elements are called (groups, periods).

37. Review Questions
The horizontal rows of elements are called periods.