THE PERIODIC TABLESection 1 – Arranging the Elements

EARLY 1860’S

About 63 elements have been identified

No organization to the elements

Several scientists are trying to find a way to

organize the elements.

DMITRI MENDELEEV

• Discovers pattern to the elements in 1869

• Grouped similar elements together

• Used properties like• Density• Appearance• Melting point

DMITRI MENDELEEV

• Arranged elements in order of increasing atomic mass

• Discovered a repeating pattern in the elements

• Predicted existence & properties of elements not yet discovered

• Created 1st periodic table

PERIODIC

Happens at a regular interval

Days of the week are periodic.

List 2 other examples of events that happen periodically.

The pattern Mendeleev discovered repeated every 7 elements.

A PROBLEM WITH MENDELEEV’S TABLE

Some element’s properties did not fit the pattern in Mendeleev’s table.

A solution is found in 1914 by Henry Moseley. Arranged the periodic table by atomic

NUMBER instead of atomic MASS.

PERIODIC LAW

The repeating chemical and physical properties of elements change periodically with the elements’ atomic numbers

METALS

Make up most of the elements on the periodic table

Located on the LEFT side of the zigzag line

Are usually SOLID at room temperature SHINY / MALLEABLE / DUCTILE GOOD CONDUCTORS of heat & electricity Outer energy levels contain FEW

ELECTRONS

VALENCE ELECTRONS

Electrons found in the outermost energy level of an atom

NONMETALS

Located on the LEFT side of the zigzag line

More than half are GASES at room temperature

DULL in color BRITTLE POOR CONDUCTORS of heat &

electricity Outer energy levels are ALMOST FULL

or FULL

METALLOIDS

Also called SEMICONDUCTORS

Found BORDERING the zigzag line

Outer energy levels are usually HALF FULL

Have properties of BOTH METALS & NONMETALS

DECODING THE PERIODIC TABLE

EVERY ELEMENT HAS A CHEMICAL SYMBOL

• Universal symbols

• 1 or 2 letters

• 1st letter: ALWAYS capitalized

• 2nd letter: NEVER capitalized

INFO FOUND IN PERIODIC TABLE BOXES

• Chemical symbol

• Element name

• Atomic number

• Atomic mass

PERIODS ON THE PERIODIC TABLE

• Horizontal rows

• 7 periods

• Element properties change as the period moves across table

GROUPS ON THE PERIODIC TABLE

• Vertical columns

• Also called FAMILIES

• 18 groups

• All elements in a group have:

- Similar properties- Same number of valence electrons