Arranging the Elements

1. Arranging the Elements

2. Dmitri Mendeleev • 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

3. Periodic Table of the Elements 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!

4. Changes to the arrangement • 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. Atomic Number Atomic Mass

5. Classes of Elements • Metals • Found to the left of the “zigzag” line • Most are solid at room temperature • Nonmetals • Found to the right of the “zigzag” line • More than ½ are gases at room temp. • Metalloids • Also known as “semiconductors” • Border the “zigzag” line • Properties of metals AND nonmetals

6. Decoding the Periodic Table • 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