The Periodic Table Part One
The Basics What does periodic mean? Having or marked by repeated cycles What things in our everyday life do we notice as cyclic or periodic? What are some of the patterns you notice on the periodic table? There are many important people who played a key role in organizing the elements in such an intricate fashion
Antoine Lavoisier (1790 s) Compiled a list of known elements at the time (23) What elements do you think were included here? Gold, silver, oxygen, carbon The 1800 s brought about big changes
What are some big things that may have affected the knowledge of chemistry? Electricity Development of the spectrometer Industrial revolution (mid-1800 s) Lead to many chemical industries soaps, dyes, fertilizers But not all good things came from the revolution Chemical pollution now an issue 70 known elements by the 1870
In addition to new elements New scientific data that provided insight into the properties of compounds and elements A tool for organization became necessary Big step: 1860 Scientists agreed on a method for accurately determining the atomic masses of the elements (finally!) What would be the problem with not having a universal way to measure the mass of elements? Now the search for relationships between mass and elements was on
John Newlands (1864) English chemist Proposed organization scheme Noticed elements were arranged by increasing atomic mass Also, their properties repeated every eigth element 1 st and 8 th 2 nd and 9 th What do were call this repeating pattern? Newlands called it: The Law of Octaves Octave is a group of musical notes that repeats every eighth tone
Newlands organized the first 14 known elements Elements with similar properties were in the same row How does this compare with our current periodic table
Newlands organized the first 14 known elements Elements with similar properties were in the same row How does this compare with our current periodic table
The Law of octaves was not readily accepted b/c it did not work with all elements Newlands law was also criticized b/c the use of the word octave was considered very unscientific The important thing was that Newland recognized that properties of elements were repeated
Lothar Meyer (1869) German chemist Demonstrated connection between atomic mass and elemental properties Did not receive as much credit as Dmitri Mendeleev because he did not publish his organization scheme first
Dmitri Mendeleev (1869) Russian chemist demonstrated connection between atomic mass and elemental properties Noticed (like Newlands) that when elements were put in order of atomic mass there was a periodic repetition of their elemental properties Arranged elements in order of increasing atomic mass into columns with similar properties This was the first periodic table
Mendeleev s table was widely accepted because it predicted the existence and properties of undiscovered elements Blank spaces on the table Predicted properties of yet to be discovered elements such as scandium, gallium, and germanium
But there were problems New elements discovered and atomic masses were more accurately determined Elements in Mendeleev s table not in correct order Arranging elements by mass now put groups of elements together with different properties
Henry Moseley (1913) English Chemist Figured out the problem with Medeleev s Table What did Moseley Discover before? Atoms of each element contain unique number of protons in their nuclei He arranged elements in order of increasing atomic number and not increasing atomic mass
Problem Solved! Moseley s arrangement solved the problems with Mendeleev s table His arrangement resulted in clear periodic patterns of properties Lead to Periodic Law: Statement that there is a periodic repetition of chemical and physical properties of the elements when they are arranged in increasing atomic number
Modern Periodic Table
What s in the box? What does the 1 stand for? Atomic Number This tells us what about an atom of H? # of protons What does the 1.007947 stand for? Atomic Mass This tells us what about an atom of H? Mass in nucleus (# of protons and neutrons)
On the modern periodic table, how are elements arranged? In order of increasing atomic number, left to right What do we call the columns (up and down) on the periodic table? GROUPS (or families) What do we call the rows (left and right) on the periodic table? PERIODS
Periods What does periodic mean? Having or being marked by repeated cycles What element does period 1 begin with? H How many periods are there on the table? 7
Groups Two different number systems for groups. In the first numbering system, groups are number 1-8 and each number is followed by either an A or B The groups labeled A are the main groups (1A thru 8A) Representative elements This is because they possess a wide range of chemical and physical properties The groups designated with a B (1B thru 8B) are found in the center Transition Elements A more recent numbering system has been devised numbering 1-18