The Periodic Table Mrs Nielsen Chemistry The History

The Periodic Table 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. A spiral periodic table Dmitri Mendeleev’s first published periodic table

The Modern Periodic Table Ø Developed by Henry Moseley in 1911 Ø Elements are organized by increasing atomic number Ø Elements with similar properties occur at regular intervals

How is the Periodic Table Arranged? Rows = “periods” Ø Properties vary across a period Columns = “groups” or “families” Ø Similar bonding capabilities Ø Elements in a compound may be replaced by other elements in the same family.

Families of Elements Group 1: Alkali Metals Highly reactive, not found as free elements in nature 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” Why are Br and Hg a different color?

Metals, Non-metals and Metalloids 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

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

The Periodic Table as a REFERENCE TOOL

How do I use the periodic table as a reference tool? 29 Cu 63. 55 Atomic # = # of protons Element Symbol Average Mass = a weighted average based on how common an isotope is.

How do I calculate average atomic mass? Examples: 1) You have 100 marbles. 25 marbles have a mass = 2. 0 g 75 marbles have a mass = 3. 0 g. 25 (2. 0 g) +. 75 (3. 0 g) = 2. 75 g 2) There are 2 forms of naturally occurring copper. Copper – 63 (69. 17%) = 62. 929598 amu Copper – 65 (30. 83%) = 64. 927793 amu. 6917 (62. 929598) +. 3083 (64. 927793) = 63. 55 amu

The mass of an element can be used to determine either the atomic mass or the molar mass. Atomic Mass Units: Atomic mass unit (amu) = the mass of 1 atom of any element. One helium atom has a mass of 4. 002 amu Molar Mass 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 32. 066 g/mol

What do these new units mean? Atomic Mass Units (amu) § 1 amu = 1. 660504 x 10 -24 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 1023 items in 1 mole.

Fun Fact: 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 1023 is a REALLY BIG number!