Mrs. Nielsen Chemistry

The History of the Periodic Table By 1860, more than 60 elements had been discovered, but scientists had no way of organizing the elements. Dmitri Mendeleev’s first published periodic table A spiral periodic table

 Developed by Henry Moseley in 1911  Elements are organized by increasing atomic number  Elements with similar properties occur at regular intervals

Rows = “periods”  Properties vary across a period Columns = “groups” or “families”  Similar bonding capabilities  Elements in a compound may be replaced by other elements in the same family.

Families of Elements Group 2: Alkaline Earth metals Highly reactive Group 3-12: Transition metals Group 17: Halogens Very reactive, often react with alkali metals Group 18: Noble Gases Unreactive, already “happy” Group 1: Alkali Metals Highly reactive, not found as free elements in nature Why are Br and Hg a different color?

Metals (“downstairs”)  good conductors of heat and electricity  malleable  ductile  tensile strength  luster Non-Metals (“upstairs”)  poor conductors of heat and electricity Metalloids (on the stairs)  semi-conductors of heat and electricity

Use the white boards with periodic tables to complete the following tasks.  Put a star around the alkali metal that has 3 protons.  Shade in the noble gas that is in the 4 th period.  Circle the halogen that is a liquid at room temperature.  Put a square around the transition metals.  Label the Lanthanide series with an L.  Label the Actinide series with an A.  Draw a triangle around 2 of the metalloids.  Put an “X” through the non–metal in Group 14.  Draw a over the alkaline earth metal with an atomic # of 20.

The Periodic Table as a REFERENCE TOOL

29 Cu Average Mass = a weighted average based on how common an isotope is. Element Symbol Atomic # = # of protons How do I use the periodic table as a reference tool?

Examples: 1) You have 100 marbles. 25 marbles have a mass = 2.0g 75 marbles have a mass = 3.0g 2) There are 2 forms of naturally occurring copper. Copper – 63 (69.17%) = amu Copper – 65 (30.83%) = amu.6917 ( ) ( ) = amu.25 (2.0g) +.75 (3.0g) = 2.75 g

The mass of an element can be used to determine either the atomic mass or the molar mass. Atomic Mass Molar Mass Units: Atomic mass unit (amu) = the mass of 1 atom of any element. One helium atom has a mass of amu Units: grams per mole (g/mol) = the mass of 1 mole of atoms of any element. One mole of sulfur atoms has a mass of g/mol

What do these new units mean? Atomic Mass Units (amu)  1 amu = x g  Carbon – 12 is set as the standard measurement at 12 amu.  Therefore, the atomic mass of any element is found by comparing its mass with Carbon-12. Grams per Mole (g/mol)  How many items are in 1 mole? Yes indeed! There are 6.02 x items in 1 mole.

The current world population is approximately 7 billion people. If everybody in the world was working together to count one mole of atoms, and each person is counting at a rate of 1 atom/second, it would take over 2.7 MILLION YEARS to count all of the atoms in one mole! Conclusion: 6.02 x is a REALLY BIG number!