History of The Periodic Table

1. History of The Periodic Table

2. Objectives • Explain how elements are organized in a periodic table • Compare early and modern periodic tables • Identify 3 broad classes of elements

3. Important Vocabulary • Triad • Law of Octaves • Periodic Law • Group • Period • Malleable • Ductile • Metalloid

4. Searching for an Organizing Principle • By 1700, only 13 elements had been identified • By the decade of 1765-1775, 5 new elements had been discovered with the increased use of the scientific method • However, as more elements were discovered in the years following, a need for a classification system became important

5. J.W. Dobereiner • In 1829, this German chemist published a classification system • Within his system, element were grouped into triads • A triad is a set of 3 elements with similar properties • Problem: all the known elements could not be grouped into triads

6. John Newlands • Was an English chemist • In 1865, he arranged the known elements according to their properties and in order of increasing atomic mass • In doing this he noticed that all the elements in a given row had similar chemical and physical properties • It seemed that this pattern repeated every eight elements • He called this observed pattern the law of octaves

7. John Newland’s Periodic Table

8. Dmitri Mendeleev • Was the inventor of the first periodic table in 1869 • He was a Russian chemist who used Newland’s observations and other information to create a table arrangement • His table only had 63 elements

9. Creating the 1st Periodic Table • He wrote a symbol for each element, along with the physical and chemical properties and the relative atomic mass of the element on cards • He arranged the elements in order of increasing atomic mass • He started a new row everything he notices the elements chemical properties repeated • In addition, he left gaps in his table for elements he predicted should fit there

11. Henry Moseley • Was an English chemist • In 1914, he found a different physical basis for the arrangement of the elements • He studied the X-ray spectra of 38 different elements and found that the wavelengths of the lines in the spectra decreased in a regular manner as atomic mass increased • He ultimately developed the concept of atomic number • Thus, the periodic table was arranged by atomic number rather than atomic mass

12. Periodic Law • States that when the elements are arranged according to their atomic numbers, elements with similar properties appear at regular intervals • So why does this happen? • It has to do with the electron configurations of elements

13. Organization of the Periodic Table • Elements in each column of the table have the same number of electrons in their outer energy level. • These outer electrons are called valence electrons • A vertical column on the periodic table is called a group • Where as a horizontal row on the periodic table is called a period

14. 3 Main Groups of Elements • Elements are classified into 3 main groups • Metals • Nonmetals • Metalloids (aka Semiconductors)

15. Metals • There are 6 types of metals in the periodic table Alkali metals Alkaline-earth metals Transition metals Rare Earth metals Synthetic metals Other metals

16. Characteristics of Metals • Many elements are classified as metals • Most of them are located in the middle of the periodic table • Metals are good conductions of heat & electric current • They are malleable and ductile • Malleablemeans that they are easily formed • Ductile means that they can be drawn into wires • Metals also haveluster

17. Nonmetals • Are found throughout the periodic table • Groups 13-16, 17 & 18 and hydrogen • They are poor conductors of heat and electric current • Only exception to this rule is carbon • Solid nonmetals tend to be brittle and will shatter if hit with a hammer • What elements do they include?

18. Semiconductors • Are intermediate conductors of heat & electricity • Also known as metalloids • Include only 7 elements: Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium and Astatine • Silicon is the most familiar semiconductor • What is it used for?