1. Chapter 3: Elements and the Periodic Table
Section 2: Organizing the Elements

2. Patterns in the Elements
Dmitri Mendeleev (19th century) noticed that a pattern of properties appeared when he arranged the elements in order of increasing atomic mass.
Atomic mass: average mass of all the isotopes of that element
Mendeleev found that the properties of elements repeated like the days of the week on a calendar.
Predicted that the blank spaces in his periodic table would be filled by elements that had not yet been discovered. He even predicted the properties of those elements.

3. Mendeleev’s Periodic Table

4. Checkpoint 1
What is atomic mass?

5. Checkpoint 1 What is atomic mass?
Average mass of all the isotopes of that element

6. The Modern Periodic Table
Periodic table: a chart of the elements showing the repeating pattern of their properties
Periodic means “in a regular, repeated pattern”
A period is a row (horizontal)
Arranged by atomic number instead of atomic mass (Henry Mosely)

8. Finding Data On Elements
Atomic Number (number of protons)
Chemical Symbols and Names
Chemical symbol: a one- or two-letter representation of an element
Average Atomic Mass (weighted average of the mass of all of the isotopes of an element)

9. Checkpoint 2
What is the difference between the way that Mendeleev arranged the periodic table and how the modern periodic table is arranged?

10. Checkpoint 2
What is the difference between the way that Mendeleev arranged the periodic table and how the modern periodic table is arranged?
Mendeleev arranged the elements by their atomic mass. The modern periodic table is arranged by increasing atomic number.

11. Calculating Average Atomic mass

12. Organization of the Periodic Table
The properties of an element can be predicted from its location in the periodic table.
Period: horizontal rows on the periodic table
As you move across a period from left to right, properties of the elements change according to a pattern
Group: vertical columns on the periodic table
a.k.a. family
Numbered from 1-18
Elements in each group have similar characteristics
Arranged like a calendar

14. Checkpoint 3
What is the difference between a period and a group?

15. Checkpoint 3 What is the difference between a period and a group?
A period is a horizontal row and a group is a vertical column.

16. Post-lesson Quiz What does it mean for something to be “periodic”?
a. it increases
b. it decreases
c. it has a regular repeating pattern
d. it is random

17. Post-lesson Quiz
2. Who developed the first periodic table? a. Henry Moseley b. Dmitri Mendeleev c. Robert Boyle d. Gregor Mendel

18. Post-lesson Quiz
3. What is the average mass of all the isotopes of an element? a. atomic mass b. atomic number c. chemical symbol d. electron configuration

19. Post-lesson Quiz
4. What is a vertical column on the periodic table called? a. line b. period c. class d. group

20. Post-lesson Quiz
5. What is a horizontal row on the periodic table called? a. line b. period c. class d. group