The Development of the Periodic Table
Dec 31, 2015
Objectives
• iWBAT
• Distinguish between groups on the periodic table (with respect to the group properties)
Johann Dobereiner (1829)
Ca Cl Li
Sr Br Na
Ba I K
Johann Dobereiner proposed that nature contained triads of elements. The middle element had properties that were an average of the other two elements when ordered (organized) by the atomic weight.Dobereiner called this the “Law of Triads”.http://www.wou.edu/las/physci/ch412/perhist.htm
J.A.R. Newlands (1866)
J.A.R. Newlands developed the “Law of Octaves”. Chemical elements were arranged according to increasing atomic weight, those with similar physical and chemical properties occur after each interval of seven elements. http://www.docbrown.info/page12/gifs/Newlands1866.gif
Dmitri Mendeleev (1869)
Dmitri Mendeleev listed the elements in columns in order of increasing atomic mass. Mendeleev then arranged the columns so that the elements
with the most similar properties were side by side. http://library.thinkquest.org/C006669/media/Chem/img/Mendeleev.jpg
Mendeleev’s Periodic Table
Mendeleev left blank spaces in the table because there were no known elements with the appropriate properties and masses.http://www.msnucleus.org/membership/html/jh/physical/periodictable/images/MendeleevPeriodic.gif
Missing Elements Predicted By Mendeleev
Ga Sc Ge
Mendeleev, and others, were able to predict the physical and chemical properties of the missing elements. Eventually these elements (Ga, Sc and Ge) were discovered and found to have properties similar to those elements Mendeleev predicted.
Henry Moseley (1913)
Moseley determined the atomic number of the atoms of the elements. He arranged the elements in a table by order of atomic number instead of atomic mass. This is the current arrangement of the periodic table. http://www.meta-synthesis.com/webbook/35_pt/pt1930.gif
Henry Moseley later modified Mendeleev’s table by organizing the elements by atomic number rather than atomic mass.
Periodic Table Labeling European notation American system IUPAC
(Inter. Union of Pure
& Applied Chemistry)
The elements in a group have similar properties because they have valence electrons in similar configurations
Roman numerals IA, IIA, IIIA 1-18 (no letters)
Periodic Law
• The Periodic Law states:
• (textbook language)
• The physical and chemical properties of the elements are periodic functions of their atomic numbers.
• (In English)
• When the elements are arranged in order of increasing atomic number, elements with similar properties appear at regular intervals.
The Modern Periodic Table
The elements are listed in order of increasing atomic number
from left to right and from top to bottom. http://www.corrosionsource.com/handbook/periodic/periodic_table.gif
Electron Configurations
• Write the electron configuration for:
• Li, Na, K
• Be, Mg, Ca
• Ne, Ar, Kr
Electron Configurations
• What do you see that is similar about each of the electron configurations in the group?
Electron Configurations
• Write the electron configuration for elements in the following groups:
• Be, Mg, Ca
• Ne, Ar, Kr
1s1
1s22s1
1s22s22p63s1
1s22s22p63s23p64s1
1s22s22p63s23p64s23d104p65s1
1s22s22p63s23p64s23d104p65s24d10 5p66s1
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67s1
H1
Li3
Na11
K19
Rb37
Cs55
Fr87
Do you notice any similarity in these configurations of the alkali metals?
Stable Octet
• Elements want to gain, or lose, electrons to have 8 valence electrons
• (or you can say a stable octet, or full octet)
Groups vs Periods
• On the Periodic Table:
• Groups are also called columns or families
• Periods are rows
Things to know about the Periodic Table:
• Main/representative group elements
• Group Names (alkali metal, alkaline earth metal, transition metal, halogens, noble gases, lanthanides, actinides)
• Solid, liquid, or gas
• Metal, non-metal, metalloid
• Valence electrons
1A
2A 3A 4A 5A 6A 7A
8A• Elements in the 1A-7A groups are
called the representative elements
outer s or p filling
Properties of Groups
• Alkali metals
• Silvery appearance
• Soft enough to be cut with a knife
• Extremely reactive with air and water
• Stored in oil (or kerosene)
• Alkali metals are not found in nature as free elements
Properties of Groups
• Alkaline earth metals
• Extremely reactive with water
• Alkaline earth metals are not found in nature as free elements
• Group 2 metals are – harder, denser and stronger and have higher melting
and boiling points than alkali metals.
Properties of Groups
• Halogens
• Very high electronegativities
• Seven valence electrons (one short of a stable octet)
• Highly reactive, especially with alkali metals and alkaline earths
Properties of Specific Element Groups
• D block elements
• Commonly called Transition metals
• Good conductors of electricity
• High luster
Properties of Specific Element Groups
• p block elements
• Contains metals, non-metals and semi-metals