1. Unit 3 Notes – Chapter 3
Chemistry
Mr. Nelson

2. Mendeleev
Dmitri Mendeleev first organized elements according to atomic mass.
He noticed similarities in their chemical properties appeared at regular intervals
Such a pattern is called periodic
Thing to remember: its just a general trend

3. Mendeleev’s first table

4. Periodic Law Mendeleev’s table has gaps! Two questions he posed:
1. Why could most elements be arranged in order of increasing atomic mass, but some couldn’t?
2. What is the reason for chemical periodicity?

5. Periodic Law
Moseley, who worked with Rutherford, discovered that atomic number, not atomic mass, is the basis of organization. This led to…
Periodic Law: The physical and chemical properties of the elements are periodic functions of their atomic numbers.

6. Periodic Table Organization
Vertical columns in the periodic table are known as groups or families

7. Periodic Table Organization
Horizontal Rows in the periodic table are known as Periods

8. Valence Electrons
Outer-most electrons

9. Periodic Table
Metals are on the left side of the chart.

10. Metals Are usually: Lustrous Malleable Ductile
good conductors of heat and electricity
Tend to lose electrons in chem rxns

11. Periodic Table
Nonmetals are on the right side of the periodic table (with the exception of H).

12. Nonmetals Are usually Dull brittle
poor conductors of heat and electricity.
Tend to gain electrons in chem rxns.

13. Periodic Table
Metalloids border the stair-step line (with the exception of Al, Po, and At).

14. Metalloids Have some characteristics of metals and nonmetals.
For Example:
Silicon looks shiny, but is brittle and fairly poor conductor.

15. Alkali Metals: Group 1 Soft! Can be cut like butter with a knife
React with O2 in air
Reacts VIGOROUSLY with water

16. Alkaline-earth Metals
Group 2
Harder, denser, higher melting points than group 1.
Reactive, but not like group 1.
Reacts with oxygen in air, like group 1.

17. Transition elements Groups 3-12 They are all metals
Harder, denser, with higher melting points (except for mercury)

18. Lanthanides: elements 57-71
Shiny, reactive metals
Actinides: elements
All have radioactive forms

19. Main block elements: groups 13-16
Named by the uppermost element
Halogens: Group 17
Reactive, all are nonmetals.

20. Noble Gases
Group 18
Escaped detection for some time due to their nonreactivity

21. Hydrogen
Group all on its own.

22. Electron dot diagram Represent valence electrons 1 dot = 1 electron
Example: Rubidium

23. Diatomic Molecules
These seven elements occur naturally as molecules containing two atoms.