1. Chapter 18, Section 3

2. Organizing the Elements
Periodic means “repeated in a pattern”
Elements are organized in the periodic table by increasing atomic number
in the late 1800’s Dmitri Mendeleev organized them in order of increasing atomic mass
he noticed a pattern of repeating chemical properties of certain elements
he was able to predict the properties and mass numbers of undiscovered elements
Problem: not all atomic masses increase from left to right! (check out cobalt & nickel)

3. Improving the Periodic Table
In 1913, Henry G.J. Moseley arranged the elements by atomic number rather than atomic mass
This corrected the problem
Good
Better!

4. The Atom and the Periodic Table
Groups: vertical columns of elements in the periodic table with similar properties
Elements in the same group have the same number of electrons in their outer energy level
Each of the seven energy levels have a maximum number of electrons they can hold
Energy level 1 = up to 2 electrons
Energy level 2 = up to 8 electrons
Energy level 3 = up to 18 electrons
Energy level 4 = up to 32 electrons

5. The Atom and the Periodic Table
Outer energy electrons affect an element’s behavior
For example, the Group 1 elements lithium sodium, potassium, rubidium, and cesium are soft silver metals that react violently with water

6. Regions on the Periodic Table
Periods: rows of the periodic table of elements; the number of protons and electrons increase from left to right
When a period ends at the far right side, the outer energy level is filled
Elements are classified as metals, nonmetals, and metalloids
Metals: solids, shiny, can be drawn into wires or pounded into sheets, good conductors of heat and electricity

7. Regions on the Periodic Table
Nonmetals: solids, liquids, & gases (if solid, it’s brittle), poor conductors of heat and electricity
Metalloids: have properties of both metals and nonmetals
Most elements above the atomic number 92 have only been discovered or created in a laboratory.

8. Elements in the Universe
The same elements exist all over the universe
Elements larger than hydrogen and helium are manufactured in stars
Dying stars eject these larger elements, sometimes violently
Supernova: star explosion

9. Review Questions, p.562 2-4 Answer these questions:
Give the period and group on which each of these elements is found: nitrogen, sodium, iodine, and mercury
Write the names of these elements and classify each as a metal, nonmetal, or a metalloid: K, Si, Ba, and S
Why do you think the chart used by Moseley was more accurate at predicting where new elements would be placed than Mendeleev’s chart?