Chemical Periodicty Patterns of Change

Topics of Discussion Periodic Table Electron Configurations Periodic Trends

Development of the Periodic Table Mid 1800’s ~ 70 elements known - coinage metals -examples: -halogens: “salt formers” -alkali metals -examples Early attempts at organizing the elements - Döbereiner’s Triads - Newland’s Law of Octaves

Döbereiner’s Triads In 1829 Döbereiner proposed the Law of Triads: The middle element in the triad had atomic weight that was the average of the other two members. The densities of some triads followed a similar pattern. Soon other scientists found chemical relationships extended beyond triads. Fluorine was added to Cl/Br/I group; sulfur, oxygen, selenium and tellurium were grouped into a family; nitrogen, phosphorus, arsenic, antimony, and bismuth were classified as another group.

Dmitri Mendeleev Russian chemist In 1869, published the first Periodic Table of the Elements Dmitri Mendeleev

Mendeleev (cont) Listed all known elements in order of increasing atomic mass Arranged the columns that elements with similar properties were side by side…even if out of order by mass.

Mendeleev’s Predictions Left blanks in the table if no element with appropriate properties was known Accurately predicted properties of missing elements “Ekaaluminum” Gallium discovered in 1875 “Ekaboron” -Scandium discovered in 1877 “Ekasilicon” -Germanium discovered in 1886 Drawbacks: didn’t account for noble gases and rare earth elements

Henry Moseley Worked with Rutherford Recorded X-ray diffraction data on the elements to determine nuclear charge

Moseley (cont) Realized that the properties of the elements are related to the number of protons in nucleus Rearranged the periodic table based on atomic number

Periodic Law When the elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties -regular and repeating pattern metalmetalloidnonmetalunreactive gas

Valence Electrons The outermost electrons in an atom lead to chemical properties The electrons in the highest occupied s and p orbitals varies from 1-8 number of valence electrons = group number ”main block” groups 1, 2, 13-18

How many valence electrons? Li N O C Ar Mg

Lewis Dot Structures/Diagrams One dot for each valence electron Li C N Ar O Mg

Modern Periodic Table Periods in horizontal rows numbered 1-7 Groups in vertical rows numbered 1-18 aka; families s block groups 1-2 p block groups 13-18 d block groups 3-12 f block lanthanides & actinides

s-, p-, d-, and f-blocks

Alternative Periodic Tables Periodic table by Emil Zmaczynski (1935)

Alternative Periodic Tables Spiral Periodic Table from Theodor Benfey (1960)

Alternative Period Table Timmothy Stowe’s Physicist Periodic Table (1988)

Atomic Size (Radius) Left right in a period size decrease more protons, therefore electrons are held more tightly Zpff increases left to right Shielding constant in a period (number of core electrons is constant)

Atomic Radius As you go down a column, the radius increases in size Outermost electrons are not held tightly by the nucleus

Ionic Radii Cations will be smaller than parent atom Fewer electron electron repulsions Anions will be larger than parent atom More electron electron repulsions

Ionization Energy From left to right, ionization energy increases in a period Number of core electrons is constant Number of protons increases Down a group, ionization energy decreases Increased shielding as you go down a column Outermost electrons feel less nuclear charge and are easily removed

Electronegativity From left to right, electronegativity increases F has the highest Down a column, electronegativity decreases Fr has the least

Summation Create a concept map from these three main concepts: Periodic Table Electron Configuration Periodic Trends