The Development of the Periodic Table

Drill

• Please place your homework in the red bucket.

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?

Valence Electrons

• Explain how similar electron configurations and valence electrons tie together.

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

Main/Representative Groups (Groups # 1, 2, 13-18…i.e. s & p)

http://0.tqn.com/d/chemistry/1/0/X/u/PeriodicTableNaturalState.jpg

• http://library.thinkquest.org/06aug/00318/Images/periodic_table.gif

Blue = metal Yellow = non-metalPink = metalloid or semi-metal

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 Groups

• Noble Gases

• He, Ne and Ar do not react with any other element.

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

Properties of Specific Element Groups

• f block elements

• Inner Transition metals

• Called Lanthanides and Actinides

• Actinides

• are all radioactive

• the first four elements are found naturally and the remaining actinides are man-made.