Periodic Table Development Chapter 6.1 Periodic Table Development

1790’s Lavoisier makes a list of all known elements (23) First compilation of elemental information

1800’s Discovery and use of electricity allows scientists to use electrolysis to decompose compounds Spectrometer invented Enables new elements to be identified Triples the number of known elements Knowledge of properties also increases and is standardized

1817 - Dobereiner Grouped elements in triads Mass of the middle element was the average of the other two

1864 - Newlands Arranged elements by increasing atomic mass Developed “Law of Octaves” Properties repeated every 8 elements Similar to notes on a piano 7 groups of 7 elements

1864 - Newlands Not a bad first attempt, but a lot of flaws Law of octaves did not work for all elements Other scientists resented the use of the word octaves as unscientific

1869 - Mendeleev Arranged elements by increasing atomic mass Put elements with similar properties in the same column Expanded Newland’s table after n=2 Put spaces for 17 elements in n=3&4 Left blank spaces and predicted properties for undiscovered elements

1869 - Mendeleev Flaw in Mendeleev’s table As atomic masses became more accurate, more elements seemed to be misplaced

1913 - Moseley Discovered the proton and atomic number Arranging elements by atomic number corrected the flaws of both Newland and Mendeleev Periodic Law – Properties of elements are periodic functions of their atomic numbers

Modern Periodic Table Periods – horizontal rows Groups/Families – vertical columns Similarities within a group Electron configurations Electron dot diagrams Reactivity of elements Group 18 (noble gases) only group with full outer energy levels and composed solely of non-metals

Classifying the Elements

Metals Left side of the periodic table Properties Hard Lustrous good conductors Malleable Ductile

Metals 3 or fewer electrons in their outer energy level Reactivity increases as you move down and left across the periodic table

Metals Group 1 – Alkali Metals Group 2 – Alkaline Earth Metals 1 electron in outer level Most reactive of all metals Group 2 – Alkaline Earth Metals 2 electrons in outer level Highly reactive

Transition Metals – Groups 3-12 1 or 2 electrons in outer level Contain numerous exceptions to the ground state electron configurations Elements with a full or partially filled sub-level are slightly more stable Properties of elements in groups are still similar Group 11 – coinage metals

Transition Metals – Groups 3-12 Often provide the color in gemstones when the transition element is substituted into a crystal Corundum (Al2O3) Cr replaces some Al producing Rubies Fe replacing Al for Topaz Ti replacing Al for Sapphire Beryl (Be3Al2Si6O18) Cr replaces Al to produce Emeralds Substitution occurs because the atoms have similar atomic radii and valence electrons

Inner Transition Metals Lanthanides & Actinides Small differences in electron configurations All elements in the family could be placed in one block of the periodic table Used as phosphors Emit light when hit with electrons Examples – TV's computer monitors

Non-Metals Right side of periodic table 5 or more electrons in their outer level Gases or brittle solids at room temperature More reactive as you move up and to the right on the periodic table

Non-Metals Group 16 (6 electrons) Group 17 (7 electrons) Chalcogens Group 17 (7 electrons) Halogens (salt former) Highly reactive Group 18 (8 electrons) Noble Gases Extremely unreactive

Metalloids Elements separating the metals from the non-metals Properties of both metals and nonmetals Properties get more metallic as you move down the group