Organizing the Elements Chapter 4, Section 2 Organizing the Elements

Mendeleev He discovered a set of patterns that applied to all elements He wrote properties of elements on individual cards He then arranged them according to increasing atomic mass (average mass of all of an element’s isotopes)

Periodic Table Group by group, Mendeleev arranged the 63 known elements based on their properties: Melting point If they tarnish If they react with water Etc. Periodic means “in a regular, repeated pattern” Table Talk: Discuss why Mendeleev put question marks in his original periodic table. (Hint, there were only 63 known elements at the time) See Discovery Education video“Periodic Table” (3:55) – from “Greatest Discoveries with Bill Nye – Chemistry”

Modern Periodic Table More than 100 elements Arranged in order of increasing atomic number (# of protons) The properties of an element can be predicted from its location on the periodic table See Active Art: http://www.phschool.com enter code cgp-1032

http://periodictable.com/ Click here to see an interactive, illustrated version of the Periodic Table

More About the Periodic Table Classes of Elements Atomic numbers increase from left to right Table is color-coded to classify types of elements Metals Non-metals Inert gases

Periods Horizontal rows The properties of the elements change from left to right in a pattern Metals on left, with most reactive metals on far left Non-metals on the right with most reactive next to the inert gases on the far right Semi-metals between the metals and non-metals Atomic mass increases from left to right And from top to bottom

Groups Vertical columns Also known as a “family” Consists of elements with similar characteristics Lanthanides and actinides do not belong in the 18 groups and have been pulled out

Table Talk: Discuss the difference between groups and periods on the periodic Table

Reading the Data Calcium In our textbook, each square on the Periodic Table lists 4 pieces of information: An element’s atomic number Chemical symbol Name Atomic mass Calcium Table Talk: Discuss what information the atomic number and atomic mass give us. See BrainPop “Periodic Table” end