Periodic Trends

What do these random squiggles have in common?

53 known elements in 1828 How many ways can these be organized? FeCuC Pb Ag S As Sn H Ni Sb Bi Pt Cl Co Zn Hg Al Si W Os Ir Nb Se Te Br U Mn I Na F Ce Au Zr Y Cr Cd P Li B Mo Sr Ti Ba Rb K O Mg Ca Ta Be Pd N

Discovery of Elements - Until 1828 Up to 1200 a.d., only 9 elements were known…any ideas? 3 new elements found from a.d. 2 from from each from and New total: 53 Elements Discovered BC AD

In 1828, Johann Wolfgang Dobereiner developed triads These are groups of three elements containing similar traits with the atomic weight of the middle element the average of the other two. Li Na K Ca 40 Sr 87 Ba 137 S Se Te (3 + 19) / 2 = 11 = Na( ) / 2 = 87 = Sr ( ) / 2 = 34 = Se

The Law of Octaves: John Newlands “The eighth element, starting from the given one, is a kind of repetition of the first, like the eighth note of an octave of music.” -- John Newlands

1869- The Periodic Law The physical and chemical properties of the elements are periodic functions of their atomic weights. Introduced by Dmitri Mendeleev - “father of the periodic table” Arrange by atomic mass

Mendeleev’s Periodic Table (original publication)

A Periodic Table of Elements Based on Mendeleev’s Periodic Law

Mendeleev predicted the existence and properties of several elements unknown at his time. He was wicked smart. Mendeleev's Predictions about Eka-Aluminum: Atomic weight:about Boiling Point:low30° C Density: Formula of Oxide:EkaAl 2 O 3 Ga 2 O 3 Formula of chloride:EkaAlCl 3 GaCl 3 Chemistry of hydroxide:EkaAl ( OH ) 3 Ga ( OH ) 3

Mendeleev attributed these discrepancies to inaccurate measurements of atomic weights. New determinations confirmed the atomic weights of the elements that were predicted. The problem of reversed pairs still existed. USING SUPER X-RAY VISION!! TO... DETERMINE ATOMIC NUMBER!!

Henry Moseley … developed the idea of atomic numbers to arrange elements by. This solved the riddle of the discrepancies in Mendeleev’s Periodic table.

From the 19th Century Physicist’s Stowe Table Benfrey’s Table

Modern Version of the Periodic Law The properties of the elements are periodic functions of their atomic numbers. There are 18 groups or families in the periodic table He Ne Ar Kr Xe Rn C Si Ge Sn Pb B Al Ga In Tl Be Mg Ca Sr Ba Ra H Li Na K Rb Cs Fr

There are 7 periods in the periodic table >

The periodic table is an ordered logical arrangement of the chemical elements into groups with similar properties.

Periodic Trends Valence Electrons:  Constant for a family with only n values changing Atomic radius  Increases to the left and down the periodic table

Ionization Energy  Energy required to remove an electron from a gaseous atom or ion in the ground state.  Increases up and to the right Examples A] 1s 2 2s 2 2p 6 B] 1s 2 2s 2 2p 6 3s 1 C] 1s 2 2s 2 2p 6 3s 1 1. Highest IE 1 ? IE 2 ? 2. Lowest IE 1 ? IE 2 ? 3. Noble Gas?

Electronegativity  tendency to attract electrons within a bond (scale 0-4.0); strength to steal electrons Electron Affinity  Change in E when an electron is added to a gaseous atom  Trend has a lot of exceptions Both increase up and to the right Noble Gases: Lowest EN: do not want any more electrons Highest IE: do not want to lose any electrons

Shielding Effect Inner electrons block outer electrons from positive pull of the nucleus Outer electrons held with less force Explains why some atoms are larger than expected.

Metallic Character Having metallic properties like conductivity, forming cations. What is most metallic halogen? Inner transition element? Alkali metal? What is most nonmetallic element?