4-2 Notes Organizing the Elements

Mendeleev’s Periodic Table 1869 Russian scientist who discovered a pattern of the elements Arranged the elements in order of increasing atomic mass (average mass of all the isotopes of an element) Then he lined them up in groups of similar properties Developed the first periodic table of elements Contained 63 elements

The Modern Periodic Table Changed as new elements were discovered Contains over 100 elements Arranged in order of increasing atomic number (not atomic mass like Mendeleev’s) Atomic number = number of protons in an atom of that element The properties of an element can be predicted from its location on the periodic table

The Periodic Table Elements are organized into rows and columns based on their atomic number.

The Periodic Table Elements are organized into rows and columns based on their atomic number. From left to right the elements are arranged in order of increasing atomic mass.

The Periodic Table Lanthanides and Actinides Elements are organized into rows and columns based on their atomic number.

Classes of Elements Open your books to pages Each colored region corresponds to a different class of elements Metals = blue Semimetals = yellow Nonmetals = light green Inert gases = dark green

Periods Horizontal rows There are 7 periods on the table, look how they are labeled on the left side of the table Properties within each period change in a pattern Notice the lanthanides and actinides have been taken out of the table and placed underneath it This is to save space and make the table easier to read Look at the expanded table on page 136

Groups Vertical columns Aka family Elements within the same groups have similar characteristics

Finding Data on Elements Each square in the periodic table lists four pieces of information: an element’s atomic number, chemical symbol, name, and atomic mass.