History of The Periodic Table

Objectives

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

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

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

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

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

John Newland’s Periodic Table

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

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

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

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

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

3 Main Groups of Elements

•Elements are classified into 3 main groups•Metals•Nonmetals•Metalloids (aka Semiconductors)

Metals• There are 6 types of metals in the periodic

tableAlkali metalsAlkaline-earth metalsTransition metalsRare Earth metalsSynthetic metalsOther metals

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• Malleable means that they are easily

formed • Ductile means that they can be drawn into

wires• Metals also have luster

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?

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?