History of the Periodic Table Antoine Lavoisier



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History of the Periodic Table


Antoine Lavoisier

  • In the late 1790s, he compiled a list of the known elements at the time.

  • This list contained 23 elements.



But times were about to change…

  • In the 1800’s, there were many changes in the world

    • Electricity
    • Spectrometer
    • Industrial Revolution
  • As a result, there was an increase in the number of known elements

    • By the 1870, there were 70 known elements


An agreement is reached…

  • Then in the 1860’s, chemist agreed upon a method for accurately determining the atomic mass of elements.



John Newlands

  • Noticed when elements were arranged by atomic mass, they repeated properties every 8th element.

  • He used the word periodic to describe this pattern

  • He gave it the name the Law of Octaves



Unfortunately…

  • Did not work for all the elements

  • Criticized because of its association with music

  • Did give others the idea of repeating properties - periodic



Lothar Meyer and Dmitri Mendeleev

  • Each made a connection between atomic mass and properties of elements



The winner is…

  • Mendeleev is given credit because his was published first

  • In addition, Mendeleev predicted unknown elements

  • However, not completely correct – new elements weren’t in correct order

  • What do you notice about elements 27 & 28 and 52 & 53?



Henry Moseley

  • Solved this problem by arranging the elements by increasing atomic number.

  • The periodic repetition of chemical and physical properties of elements when arranged by atomic number is now known as Periodic Law



Which leads to the Modern Periodic Table

  • Boxes each with:



Remember

  • Atomic number = the number of protons = the number of electrons (if neutral)

  • Atomic Mass on the Periodic table is the average mass of the isotopes

    • But the mass number of each isotope is the protons plus the neutrons


Chemical Symbol

  • The symbol that refers to the element

  • First letter is capitalized, second letter (if applicable) is lower case

  • Not all symbols are based on English names for the elements, some come from their Latin names or even other languages



Columns and Rows

  • The columns are called Families or Groups

    • Earlier Version had 1-8 followed by A or B
      • Group A elements are called Representative Elements
      • Group B elements are called Transition Elements
    • Modern Version labels the columns with 1-18
  • Rows are called Periods

    • Seven periods for the seven energy levels (rings)


Classifying Elements

  • Three Types of Elements

    • Metals
    • Nonmetals
    • Metalloids


Metals

  • Shiny when smooth and clean

  • Solid at room temperature

    • Only exception - Mercury
  • Good conductors of heat and electricity

  • Most are ductile and malleable





Nonmetals

  • Upper Right side of the Periodic Table

  • Generally brittle solids or gases

  • Poor conductors of heat and electricity

  • Bromine is the only liquid at room temperature





Metalloids

  • A.k.a – the semi-metals

  • Boxes bordering the stair-step

  • Physical and chemical characteristics of both metals and nonmetals





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