Periodic Law
Development of a Periodic Table
Mendeleev arranged the elements in order of increasing atomic mass. 
All of the elemetns in a column had the same valence and showed similar chemical and physical properties.
Empty spaces in Mendeleev's periodic table proved to be undiscovered elements.
The Modern Periodic Table
Moseley's discovery of atomic number altered Mendeleev's periodic table.
In the modern periodic table, elements are arranged in order of increasing atomic number. 
The periodic law states that the physical and chemical properties of the elements are periodic functions o ftheir atomic numbers.
Horizontal rows in the periodic table are called periods.
Using the Periodic Table
Each element occupies on square in the table.
  Each square contains the element's atomic number, symbol, name, and atomic mass.
The elements can be classified as metals, nonmetals, or metalloids.
Metals:  good conductors of heat and electricity, shiny, high melting points, ductile, malleable.
Nonmetals: poor conductors of heat and electricity, dull, low melting points, brittle.
Metalloids: properties of both metals and nonmetals
Periodic Properties of the Elements
Periodic properties of the elements include electron arrangement, reactivity, atomic size, and metallic properties.