The Periodic Table

Chapter 5

Organizing the Elements

Chapter 5 Section 1

Antoine Lavoisier 1750- Scientists had

only identified 17 elements.

1789 Lavoisier grouped elements into metals, nonmetals, gases and earths.

For the next 80 years, scientists looked for different ways to classify the elements.

History of the Periodic Table Mendeleev wanted to

organize the elements according to their properties

Noticed periodic- repeating patterns of chemical behavior once he organized the elements

Mendeleev arranged the elements into rows in order of increasing mass so that elements with similar properties were in the same column.

A periodic table is an arrangement of elements in columns, based on a set of properties that repeat from row to row.

History of the Periodic Table

The first Periodic Table of the Elements

Mendeleev’s Prediction He could not make a complete table

because some of the elements were not discovered yet.

He left gaps in his periodic table, confident that one day new elements would be discovered.

He used the properties of elements located near the blank spaces to predict the properties for undiscovered elements.

Evidence supported Mendeleev

I LOVE SCIENCE !

There was a close match between what Mendeleev predicted and the actual properties of the new elements.

This showed how useful his periodic table really was!

The Modern Periodic Table

Chapter 5 Section 2

Organization In the modern periodic table, elements are

arranged by increasing atomic number.

Periods=rows across the table

◦ A. Atomic number increases by one from left to right across a period.

◦ B. Each time the outermost electron orbit becomes full, a new period is started.

◦ C. Look at Period 1-it only has two elements (hydrogen and helium)

Q: Why is lithium (element #3) located in Period 2?

A: The first electron orbit can only hold two electrons. The third electron in lithium must be placed in the second electron shell. Therefore, a new period (row) is started.

Groups= columns down the table

All the elements in a group have similar properties.

For example, the elements in group 1A are very reactive, whereas, the elements in group 8A are very stable.

Periodic Law: There is a pattern of repeating chemical properties in a group on the periodic table.

Elements with similar properties fall in same column or group in the periodic table.

Metals Good conductors of electric current and

heat Most are malleable and ductile (able to be

drawn through a thin wire) Metals have fewer than four electrons on

the outermost shell.

Classes of Elements- Metals

Elements that form a bridge between the elements on the left and right sides of the table.

Transition Metals

Poor conductors of electric current and heat.

Many are gases at room temperature Low boiling points Those that are solid tend to be brittle Nonmetals have more than four electrons

on the outermost shell (H and He are the exceptions)

Classes of Elements-Nonmetals

Have properties in between metals and nonmetals

Located on staircase between element #5 and element #85

Classes of Elements-Metalloids

Elements become less metallic in their properties as you move from left to right on the periodic table.

Variation Across a Period