Presentation on theme: "Section 1 – Arranging the Elements. About 63 elements have been identified No organization to the elements Several scientists are trying to find."— Presentation transcript:
About 63 elements have been identified No organization to the elements Several scientists are trying to find a way to organize the elements.
Discovers pattern to the elements in 1869 Grouped similar elements together Used properties like Density Appearance Melting point
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
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.
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.
The repeating chemical and physical properties of elements change periodically with the elements’ atomic numbers
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
Electrons found in the outermost energy level of an atom
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