Chapter 18, Section 3 http://61.19.145.8/student/m5year2006-2/502/group11/periodic_table.gif

Organizing the Elements Periodic means “repeated in a pattern” Elements are organized in the periodic table by increasing atomic number in the late 1800’s Dmitri Mendeleev organized them in order of increasing atomic mass he noticed a pattern of repeating chemical properties of certain elements he was able to predict the properties and mass numbers of undiscovered elements Problem: not all atomic masses increase from left to right! (check out cobalt & nickel)

Improving the Periodic Table In 1913, Henry G.J. Moseley arranged the elements by atomic number rather than atomic mass This corrected the problem Good Better! http://upload.wikimedia.org/wikipedia/commons/b/bb/Mendeleev's_1869_periodic_table.png http://kr.cs.ait.ac.th/~radok/physics/periodic.gif

The Atom and the Periodic Table Groups: vertical columns of elements in the periodic table with similar properties Elements in the same group have the same number of electrons in their outer energy level Each of the seven energy levels have a maximum number of electrons they can hold Energy level 1 = up to 2 electrons Energy level 2 = up to 8 electrons Energy level 3 = up to 18 electrons Energy level 4 = up to 32 electrons

The Atom and the Periodic Table Outer energy electrons affect an element’s behavior For example, the Group 1 elements lithium sodium, potassium, rubidium, and cesium are soft silver metals that react violently with water http://www.youtube.com/watch?v=Ft4E1eCUItI http://www.youtube.com/results?search_query=sodium+in+lake&search_type=&aq=6&oq=sodium

Regions on the Periodic Table Periods: rows of the periodic table of elements; the number of protons and electrons increase from left to right When a period ends at the far right side, the outer energy level is filled Elements are classified as metals, nonmetals, and metalloids Metals: solids, shiny, can be drawn into wires or pounded into sheets, good conductors of heat and electricity

Regions on the Periodic Table Nonmetals: solids, liquids, & gases (if solid, it’s brittle), poor conductors of heat and electricity Metalloids: have properties of both metals and nonmetals Most elements above the atomic number 92 have only been discovered or created in a laboratory. http://www.accessscience.com/images/periodic_table.gif

Elements in the Universe The same elements exist all over the universe Elements larger than hydrogen and helium are manufactured in stars Dying stars eject these larger elements, sometimes violently Supernova: star explosion http://upload.wikimedia.org/wikipedia/commons/thumb/d/d4/Keplers_supernova.jpg/300px-Keplers_supernova.jpg

Review Questions, p.562 2-4 Answer these questions: Give the period and group on which each of these elements is found: nitrogen, sodium, iodine, and mercury Write the names of these elements and classify each as a metal, nonmetal, or a metalloid: K, Si, Ba, and S Why do you think the chart used by Moseley was more accurate at predicting where new elements would be placed than Mendeleev’s chart?