Periodic Law
• There is a periodic repetition of chemical and physical properties of elements when arranged by increasing atomic number
History of the Periodic Table
• End of the 1700’s – less than 30 elements known
• Many elements discovered during 1800’s
• Many experiments done to determine atomic masses
John Newlands
• 1864: if elements arranged by atomic mass - properties repeat every 8th element
• Law of Octaves – did not work for all known elements
• Key idea was correct: Properties of elements do repeat in periodic way
Mendeleev & MeyerMendeleev produced 1st accepted PT: 1869•Elements ordered by ↑ atomic mass into columns with similar properties•Predicted existence & properties of undiscovered elements•Not totally correct
– more accurate atomic mass calculations showed some elements weren’t in right place
1913 – Henry Moseley
• by 1913, protons & electrons discovered– Neutrons were predicted
• Moseley determined atoms of each element contain unique # protons (= atomic number)
• rearranged Mendeleev’s PT by atomic number instead of mass
• problems with elements in wrong place disappeared
Valence Electrons – electrons in the outer shell
• Chemical behaviour determined by # valence electrons
• Elements with same # valence electrons will have similar chemical properties
–Elements in same column have similar chemical properties
Going Down Column 1:
2-8-18-32-18-8-1Fr7
2-8-18-18-8-1Cs6
2-8-18-8-1Rb5
2-8-8-1K4
2-8-1Na3
2-1Li2
1H1
ConfigurationElementPeriod
Names of Families(AKA group A elements)
• Group 1 = Alkali Metals
• Group 2 = Alkaline Earth Metals
• Groups 3-12: Transition metals
• Group 17 = Halogens
• Group 18 = Noble Gases
Inner Transition Metals
• Lanthanide (rare Earth metals) – can be found naturally on Earth, only 1 is radioactive
• Actinide– all are radioactive, some are made in the lab. INCLUDES Uranium