1. The Modern Periodic Table
Section 2
The Modern Periodic Table
The Elements

2. Key Concepts How is the modern periodic table organized?
What does the atomic mass of an element depend on?
What categories are used to classify elements on the periodic table?
How do properties vary across a period in the periodic table?

3. On this synthesizer keyboard, there is a repeating pattern of notes.
The eight-note interval between any two notes
with the same name is an octave.
Observing How many octaves are visible on the keyboard?
Middle C
G A B C D E F G A B
D E F G A B C D E F G

4. The Periodic Law
Mendeleev developed his periodic table before the discovery of protons.
Henry Moseley

5. The Periodic Law Henry Moseley
Protons were discovered in 1911 by Rutherford (Atomic Number)
Moseley used Atomic number to arrange the elements
All of the elements with similar properties fell into place.

6. The Periodic Law

7. Henry Moseley’s Periodic Table: The Modern Periodic Table

8. The Periodic Law
In the modern periodic table, elements are arranged by increasing atomic number (number of protons).
States that the physical and chemical properties of the elements are periodic functions of their atomic number.

9. The Periodic Law Periods
Each row in the table of elements is a period.
Period 1 has 2 elements. Periods 2 and 3 have 8 elements. Periods 4 and 5 have 18 elements. Period 6 has 32 elements.
Elements within a period are not similar in properties

10. The Periodic Law Groups or Families
Each column on the periodic table is called a group or family.
The elements within a group have similar properties.
The elements in a group have similar electron configurations.
An element’s electron configuration determines its chemical properties
This pattern of repeating properties is the periodic law.

11. Atomic Mass
The Elements
Atomic mass is a value that depends on the distribution of an element’s isotopes in nature and the masses of those isotopes.

12. Element Key
This box provides four pieces of information about the element chlorine: its symbol, its name, its atomic number, and its atomic mass.
Atomic
Number 17 Cl
Chemical
Symbol
Chlorine
Atomic
Mass
35.453

13. Atomic Mass Weighted Averages 34.969amu x 0.7578 = 26.499amu 26.499amu
Appears on the Periodic Table

14. Classes of Elements
Elements are classified as metals, nonmetals, and metalloids.

15. Classes of Elements Metals
Elements that are good conductors of electric current and heat.
Most metals are malleable and ductile.
Some metals are extremely reactive and some do not react easily.
Except for mercury, metals are solids at room temperature.
Found to the left of the staircase on the Periodic Table

16. Metals

17. Classes of Elements Nonmetals
Elements that are poor conductors of heat and electric current.
Tend to be brittle
Some nonmetals are extremely reactive, some hardly react at all, and some fall somewhere in between.
Found to the right of the staircase on the Periodic Table

18. Nonmetals

19. Classes of Elements Metalloids
Elements with properties that fall between those of metals and nonmetals.
A metalloid’s ability to conduct electric current varies with temperature.
Pure silicon (Si) and germanium (Ge) are good insulators at low temperatures and good conductors at high temperatures.
Found on the staircase on the Periodic Table.

20. Metalloids

21. Variation Across a Period
Across a period from left to right, the elements become less metallic and more nonmetallic in their properties.
The properties within a period change in a similar way from left to right across the table
Sodium Magnesium Aluminum Silicon Phosphorus Sulfur Chlorine Argon

22. Reviewing Concepts
1. What determines the order of the elements in the modern periodic table?
2. Describe the periodic law.
3. What two factors determine the atomic mass of an element?
4. Name three categories that are used to classify the elements in the periodic table.
5. What major change occurs as you move from left to right across the periodic table?