Arranging the Elements

• Russian chemist• 1869 – discovered a pattern to the elements• Grouped the elements according to their

similar properties and eventually arranged them in order by atomic mass.

THIS CREATED THE PERIODIC TABLE OF THE ELEMENTS

Dmitri Mendeleev

Where did the name come from??• Periodic means “happening at regular

intervals”• When arranged by atomic mass, the elements’

properties repeated themselves every seven elements.

• By using the pattern, Mendeleev predicted elements that hadn’t been discovered yet!

Periodic Table of the Elements

• Mendeleev’s table had a few elements that didn’t fit the pattern.

• Henry Moseley changed the table to be arranged by atomic number instead of atomic mass…this fixed the problem.

Changes to the arrangement

Atomic Number

Atomic Mass

• Metals– Found to the left of the “zig zag” line– Most are solid at room temperature

• Nonmetals– Found to the right of the “zig zag” line– More than ½ are gases at room temp.

• Metalloids– Also known as “semiconductors”– Border the “zig zag” line– Properties of metals AND nonmetals

Classes of Elements

1. Each element is identified by a chemical symbol

2. Rows are called Periods• Physical and chemical properties of elements in a row

follow a repeating (periodic) pattern

3. Columns are called Groups• Groups have similar chemical and physical properties

DECODING THE PERIODIC TABLE