1. Section 1 – Arranging the Elements

2.  About 63 elements have been identified  No organization to the elements  Several scientists are trying to find a way to organize the elements.

3. Discovers pattern to the elements in 1869 Grouped similar elements together Used properties like Density Appearance Melting point

4. Arranged elements in order of increasing atomic mass Discovered a repeating pattern in the elements Predicted existence & properties of elements not yet discovered Created 1 st periodic table

5.  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.

6.  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.

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

8.  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

9.  Electrons found in the outermost energy level of an atom

11.  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

13.  Also called SEMICONDUCTORS  Found BORDERING the zigzag line  Outer energy levels are usually HALF FULL  Have properties of BOTH METALS & NONMETALS

16. Universal symbols 1 or 2 letters 1 st letter: ALWAYS capitalized 2 nd letter: NEVER capitalized

17. Chemical symbol Element name Atomic number Atomic mass

18. Horizontal rows 7 periods Element properties change as the period moves across table

19. Vertical columns Also called FAMILIES 18 groups All elements in a group have: - Similar properties - Same number of valence electrons