PERIODIC TABLE Where it all is

The Beginning Law of Triads: In 1817 Johann Dobereiner noticed that the atomic weight of strontium fell midway between the weights of calcium and barium, elements possessing similar chemical properties. In 1829, after discovering the halogen triad composed of chlorine, bromine, and iodine and the alkali metal triad of lithium, sodium and potassium He proposed that nature contained triads of elements The middle element had properties that were an average of the other two members when ordered by the atomic weight.

History John Newlands determined a repeating pattern of every 8 elements. He called it the law of octaves. Developed in the 1860’s Dmitri Mendeleev arranged the first on based on Atomic Masses. Henry Moseley Arranged the Modern Periodic Table based on Atomic Number.

Who was first? There has been some disagreement about who deserves credit for being the "father" of the periodic table: the German Lothar Meyer or the Russian Dmitri Mendeleev. Both chemists produced remarkably similar results at the same time working independently of one another. Meyer's 1864 textbook included a rather abbreviated version of a periodic table used to classify the elements. Unfortunately for Meyer, Mendeleev's table became available to the scientific community via publication (1869) before Meyer's appeared (1870).

Mendelev’s Table Mendeleev’s table as published in 1869, with many gaps and uncertainties

How is it Arranged? Based on increasing atomic number (protons)and on electron configurations (valence) Results in repeating chemical(valence) and physical properties (protons). Groups or Families Columns that go up and down. (valence electrons) There are 18 Groups Periods Rows that go across There are 7 Periods (energy levels)

Classification of Elements Metals On the left side (lower left is most metallic) Make up ¾ of all elements Malleable, Ductile, Conduct electricity, form positive ions. NonMetals On the Right side Dull, Brittle, Insulators, form negative ions Metalloids (Semimetals) Found along the staircase between metals and nonmetals, have properties of both.

Group 1 – Alkali Metals Highly reactive Replace Hydrogen in Water All have 1 valence electron All are s1 (electron configuration) Forms +1 ions

Group 2 – Alkaline Earth Metals Very reactive Don’t replace Hydrogen in Water Readily burn in O2 when exposed to heat Calcium makes up your bones. Batteries get their name from this group Have 2 Valence electrons All are s2 – forms +2 ions

Transitional Metals Groups 3 to 12 These are the common metals All have d orbitals filling Less reactive than other metals Copper, Silver, and Gold least reactive Forms various positive ions All have either 1 or 2 valence electrons

Boron Family – Group 13 Have 3 Valence electrons All are s2 p1 All form +3 ions One is a metalloid (Boron) The rest are all metals Metals in this group are called Poor Metals

Carbon Family – Group 14 Carbon family has 4 valence electrons All are s2 p2 Composed of: one non-metal (Carbon) Two metalloids (Silicon and Germanium) Two Poor metals (Tin and Lead)

More on Group 14 Carbon always forms 4 bonds All known life based on Carbon Bonds with itself easily to form chains Computers function based on Silicon and Germanium’s unique properties They conduct electricity but not heat Lead and Tin are common metals Lead (Pb) Plumbum and Tin (Sn) Stannum

Group 15 – Nitrogen Family All have 5 valence electrons All are s2 p3 Composed of: two nonmetals - Nitrogen and Phosphorous Two metalloids – Arsenic and Antimony One metal - Bismuth

Some facts on 15 Nitrogen: Phosphorous makes up most of the atmosphere (78%) Critical to plant and animal life Forms strong bonds that are used in explosives Phosphorous Arsenic and Antimony have been used as poisons Bismuth used in Pepto Bismol

Group 16 – Oxygen Family All have 6 valence electrons Composed of: All are s2 p4 Usually form 2 bonds Form – 2 ions (except Polonium +2, +4 ions) Composed of: 3 nonmetals – Oxygen, Sulfur, Selenium 1 metalloid – Tellurium Polonium is classified as a metalloid but this is disputed by some that believe it to be a metal. It is highly radioactive.

Group 17 - Halogens All have 7 valence electrons All are nonmetals All are s2 p5 Forms 1 bond Forms -1 ions All are nonmetals Highly reactive Never found in nature as single atoms When pure will form F2, Cl2, Br2, I2

Group 18 – Noble Gases All have 8 valence electrons except Helium All are s2 p6 (except Helium-1s2) e-config Rarely form bonds Never form ions Helium, Neon, Argon have never been found in a compound Krypton, Xenon, Radon can sometimes be forced to form compounds – but these are very unstable Form bright colors when electricity runs through them

Actinides and Lanthanides Called Rare Earth Metals Not actually rare just hard to find 99-103 are synthetics Some are radioactive (61,93-103) All elements greater than Uranium (92) are primarily manmade but also found naturally Some are used in medical research Also used in electronic equipment

TRENDS Atomic Radius – The size of the atom. Hard to measure due to cloud not being distinct Smaller Up and Right Negative Ions Larger Positive Ions Smaller Ionization Energy – The energy required to remove one electron, the more electrons removed, the more energy required. Greater Up and Right Fluorine the highest Francium the lowest

More on Trends Electronegativity – The ability of atoms to attract electrons during bonding Greater Up and Right Fluorine the Greatest Electronegativity Francium the Lowest Octet Rule – Atoms Tend to gain, lose or share electrons to have a full (s2, p6) valence energy level Shielding Effect – The ability of inner electrons to shield valence electrons from the nucleus. Increase Down, Across Same