Learning Objectives

• Describe the organization of the modern periodic table.

• Explain how to read an element's information on the table.

• Differentiate between periods and groups.

• Identify the properties of key chemical families or groups.

Key Vocabulary

Periodic Table

A chart that organizes elements by their atomic number and shared chemical properties.

Atom

The smallest unit of matter, made of a nucleus with protons, neutrons, and electrons.

Atomic Number

The count of protons in an atom's nucleus, which is also the electron count.

Period

A period is a horizontal row in the periodic table where elements have the same number of electron shells.

Group

A vertical column in the periodic table with elements that share similar chemical properties.

What is the Periodic Table?

• It is a system that organizes elements by atomic number and properties.

• Elements are arranged by increasing atomic number, which is the number of protons.

• The table grew from 63 elements in Mendeleev's time to over 100.

• Some unstable elements are man-made by bombarding elements like Uranium.

Reading an Element's Square

• The chemical symbol is a one or two-letter abbreviation for the element.

• ​The atomic number indicates the number of protons and electrons in a neutral atom.

• Atomic mass is the combined mass of all protons and neutrons in the nucleus.

• The number of neutrons is found with the formula:

  Number of neutrons = Mass number - Atomic number.

Periods: The Horizontal Rows

• A period is a horizontal row on the periodic table; there are seven.

• Moving left to right, the atomic number of each element increases by one.

• A new period begins when a new energy level starts filling with electrons.

• Lanthanides and actinides fit into the larger periods 6 and 7.

Groups: The Vertical Columns

• A group, or family, is a vertical column on the periodic table.

• Elements in a group share properties because they have similar valence electrons.

• There are 18 groups, numbered 1 to 18 from left to right.

• For group 17, the elements have 7 valence electrons in their outer shell.

Properties of Specific Groups

• Group 1 alkali metals are very reactive and have one valence electron.

• Group 2 alkaline earth metals are reactive and have two valence electrons.

• Groups 3-12 are transition metals that are known to conduct electricity.

• Group 17 halogens are highly reactive nonmetals that form salts with metals.

• Group 18 noble gases are stable with a full outer shell of electrons.

Common Misconceptions

Summary

• The periodic table organizes elements by atomic number into periods and groups.

• Each element's square shows its symbol, atomic number, and atomic mass.

• Periods are horizontal rows that indicate the principal energy level.

• Groups are vertical columns containing elements with similar properties and valence electrons.