Periodic Table

Mysteries of Matter http://www.pbs.org/program/mystery-matter/ Please note how Mendelev arranged the elements to form the periodic table we use today.

Johann Dobereiner– German Found that Ca, Ba and Sr were very similar. He noted that the atomic mass of strontium was about midway between the other two. He grouped these elements--- triads

“Triads” suggest an underlying pattern Ca = 40 Sr = 87 Ba = 137 (40+137)/2 = 88.5 Cl = 35.5 Br = 80 I = 127 (35.5+127)/2 = 81.2 K = 39 Rb = 85 Cs = 133 (39+133)/2 = 86 S = 32 Se = 78 Te = 125 (32+125)/2 = 78.5 Johann Döbereiner Jena, Germany 1829 P = 31 As = 75 Sb = 122 (31+122)/2 = 76.5

John Newlands– 1863 English Chemist He arranged the elements in order of their increasing atomic masses. He noted that there appeared to be a repetition of similar properties every eighth element. He placed seven elements in each group. He arranged the 49 elements known at that time into seven groups of seven each Law of Octaves

1869– Dmitri Mendeleev---Russian Chemist Properties of the elements were a function of their atomic masses but that the similar properties occurred after periods that could vary in length. He placed seven elements in each of the first two periods and seventeen elements in the next two.

Mendeleev Mendeleev had to leave some blank spots in order to group all the elements in the same column To explain these blanks spots he suggested that there must be other elements to be discovered. He predicted what properties and atomic masses that these would have and he was very close

Mendeleev’s Periodic Table He arranged the elements by atomic mass

1913 Henry Moseley Something was wrong with Mendeleev’s table Te and I are in the wrong column if they are to be arranged by atomic mass X-ray experiments showed that the nucleus of each element has an integral positive charge, the atomic number

Modern Periodic Table The modern periodic table is now based on atomic number instead of atomic mass

Sir William Ramsey University College (London) A new family of elements?! Sir William Ramsey University College (London) New gas isolated from the atmosphere!

A new column is needed for the new element!

Another gas discovered! (was originally seen in the sun)

Two more gases discovered!

Another gas discovered ! (Table needs to be restacked)

Niels Bohr Copenhagen, Denmark

Glenn Seaborg Berkeley, California 1937 Only one left to be discovered! 1940 1939

Promethium was discovered in an atomic pile in Oak Ridge, Tennessee (1945) And the transuranium elements were discovered by Seaborg and others. . . .

Periodic Trends Radius Ionization Energy Electron Affinity Electronegativity

Relative Atomic Sizes Can Be Predicted by the Periodic Table Atomic Size = Atomic Radius Down a Group, Atomic Size Increases Higher Primary Shells Across a Period (lr), Atomic Size Decreases Same Primary Shell More Protons, More Electrons The + Charge from p+ Pulls All e- In

Relative Atomic Sizes of the s- and p-Block Elements Figure: 09-37 Title: Relative atomic sizes of the representative elements Caption: Atomic size decreases as you move to the right across a period and increases as you move down a column in the periodic table.

Relative Ionization Energy Can Be Predicted from Periodic Table Ionization Energy is the Energy Required to Remove One Electron from an Atom in the Gaseous State X(g)  X+(g) + e-(g) First Ionization Energy X+(g)  X2+(g) + e-(g) Second Ionization Energy... Ionization Energy Increases Across a Period Ionization Energy Decreases Down a Group The attractive forces between the nucleus and electrons are tempered by distance. Valence electrons are shielded from nucleus by all the core electrons.

Figure: 09-38 Title: Ionization energy trends in the periodic table Caption: Ionization energy increases as you move to the right across a period and decreases as you move down a column in the periodic table.

Electronegativity The Relative ability to attract electrons in a chemical bond

Octet Rule Atoms tend to gain, lose or share electrons to acquire 8 valence electrons

Radius changes in the formation of ions Cation--- Positively charged ion Lose electrons, the radius gets smaller Anion-- Negatively charged ion Gain electrons, the radius gets larger