1. Chapter 12 - The Periodic Table
Section 1 – Arranging the Elements (pp

2. DEFINITIONS Periodic – having a regular, repeating pattern
Periodic Law – states that the chemical and physical properties of elements are periodic functions of their atomic numbers
Period – horizontal row of elements
Group – column of elements

3. DISCOVERING A PATTERN
Dmitri Mendeleev began looking for patterns among properties of elements
He included density, appearance, atomic mass, melting point

4. DISCOVERING A PATTERN
Mendeleev saw a repeating pattern to the elements.
When the elements were arranged in order of increasing atomic mass, he observed similar chemical and physical properties in every eighth element.
There were some elements missing in this arrangement.

5. CHANGING THE ARRANGEMENT
Moseley determined the number of protons (the atomic number) of each element.
He arranged the elements according to their atomic number.
The Periodic Law says that the properties of each element is a periodic function of its atomic number.

6. FINDING YOUR WAY AROUND THE PERIODIC TABLE
There are 3 classes of elements. They are:
Metals
Nonmetals
Metalloids (or semiconductors)

7. METALS Most of the elements are metals.
Metals are found to the left of the zigzag line on the Periodic Table.
Most have few electrons in their outer energy level
Most are solid at room temperature.

8. METALS (cont.) Most are malleable. Most are ductile.
Most tend to be shiny.
Most are good conductors of thermal energy and electricity.

9. NONMETALS Found to the right of the zigzag line on the Periodic Table.
Most have an almost complete set of electrons in their outer energy level.
More than half are gases at room temperature.
Most are not malleable, ductile and not shiny (dull).

10. METALLOIDS (SEMICONDUCTORS)
Border the zigzag line on the Periodic Table
Have about a half-complete set of electrons in their outer energy levels.
Have some properties of metals and some of nonmetals.

11. ELEMENTS Each element is identified by a chemical symbol.
The symbol is one, two or three letters.
The first letter is capitalized; the second (and third, if applicable) is always lower case.

12. PERIODIC TABLE
Each horizontal row of elements is called a period. Periods go from left to right.
Each column is called a group or family.
Groups (or families) go from top to bottom.