Element Information
Atomic Numbers 31 through 40
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    This page contains basic information about elements with atomic numbers 31-40.  I have tried to make sure the information is correct, but if you find a mistake, please e-mail me at apurdy@centurytel.net, and I will correct it as soon as possible.

Gallium                         multicolored.gif (1741 bytes)  Click here to return to periodic table

Symbol Ga Name Gallium
Atomic Number 31 Atomic Mass 69.72 amu
Melting Point 29.78°C Boiling Point 2403°C
Protons/Electrons 31 Neutrons 39
Classification Other Metal State Solid
Density 5.904 g/cm3 Period/Group 4 / 13
Electronegativity 1.81 Atomic Radius 135 pm
# of Isotopes 2 Color silvery-blue
Energy Levels 4 Crystal Structure orthorhombic
Gallium was discovered in 1875 by Paul-Émile Lecoq de Boisbaudran.  Soon afterward he isolated the metal and found that its properties coincided with those Dimitri Mendeleev had predicted a few years earlier for eka-aluminum.                                      

Uses - photocells, transistors

 

Germanium                    multicolored.gif (1741 bytes)  Click here to return to periodic table           

Symbol Ge Name Germanium
Atomic Number 32 Atomic Mass 72.59 amu
Melting Point 937.4°C Boiling Point 2830°C
Protons/Electrons 32 Neutrons 41
Classification Metalloid State Solid
Density 5.323 g/cm3 Period/Group 4 / 14
Electronegativity 2.01 Atomic Radius 122.3 pm
# of Isotopes 5 Color gray-black
Energy Levels 4 Crystal Structure cubic
Although germanium was not discovered until 1886 by Clemens Winkler, a German chemist, its existence, properties, and position in the periodic table had been predicted in 1871 by the Russian chemist Dimitri Ivanovich Mendeleev, who called the hypothetical element ekasilicon.            

Uses - semiconductor, gamma radiation detection, transistors, wide-angle lenses, phosphor in fluorescent lamps

 

Arsenic                         multicolored.gif (1741 bytes)  Click here to return to periodic table           

Symbol As Name Arsenic
Atomic Number 33 Atomic Mass 74.9216 amu
Melting Point 814°C Boiling Point Sublimes when heated strongly
Protons/Electrons 33 Neutrons 42
Classification Metalloid State Solid
Density 5.73 g/cm3 Period/Group 4 / 15
Electronegativity 2.18 Atomic Radius 120 pm
# of Isotopes 1 Color gray
Energy Levels 4 Crystal Structure rhombohedral
Compounds of arsenic were known as early as the 4th century B.C., but it was not identified as an element until 1649.

Uses - photocells (combined with gallium), poisons, bronzing

 

Selenium                     multicolored.gif (1741 bytes)  Click here to return to periodic table              

Symbol Se Name Selenium
Atomic Number 34 Atomic Mass 78.96 amu
Melting Point amorphous - 50°C
gray - 217°C		 Boiling Point 685°C
Protons/Electrons 34 Neutrons 45
Classification Nonmetal State Solid
Density amorphous - 4.28g/cm3
gray - 4.79 g/cm3		 Period/Group 4 / 16
Electronegativity 2.55 Atomic Radius 119 pm
# of Isotopes 6 Color black
Energy Levels 4 Crystal Structure hexagonal
Selenium was recognized as an element in 1818 by Jöns Jacob Berzelius, a Swedish chemist.                                    

Uses - xerography, medicines, photoelectric cells, TV cameras, photographic toner

 

Bromine                         multicolored.gif (1741 bytes)  Click here to return to periodic table            

Symbol Br Name Bromine
Atomic Number 35 Atomic Mass 79.909 amu
Melting Point -7.2°C Boiling Point 59°C
Protons/Electrons 35 Neutrons 45
Classification Nonmetal State Liquid
Density 3.12 g/cm3 Period/Group 4 / 17
Electronegativity 2.96 Atomic Radius 114 pm
# of Isotopes 2 Color reddish-brown
Energy Levels 4 Crystal Structure orthorhombic
Antoine Jérôme Balard in France first isolated bromine in 1826 from bitterns left after the evaporation of Mediterranean Sea water and recognized it as an element in 1826.  Balard was only 23 years old.                

Uses - pesticides, photography, fumigants, flameproofing agents, dyes, medicines, water purification

 

Krypton                          multicolored.gif (1741 bytes)  Click here to return to periodic table           

Symbol Kr Name Krypton
Atomic Number 36 Atomic Mass 83.80 amu
Melting Point -156.6°C Boiling Point -152.3°C
Protons/Electrons 36 Neutrons 48
Classification Nobel Gas State Gas
Density 0.003733 g/cm3 Period/Group 4 / 18
Electronegativity 3 Atomic Radius 112 pm
# of Isotopes 6 Color colorless
Energy Levels 4 Crystal Structure cubic
Krypton was discovered in 1898 by the English chemists Sir William Ramsay and Morris W. Travers.                           

Uses - lamps, UV lasers

 

Rubidium                    multicolored.gif (1741 bytes)  Click here to return to periodic table               

Symbol Rb Name Rubidium
Atomic Number 37 Atomic Mass 85.4678 amu
Melting Point 389°C Boiling Point 688°C
Protons/Electrons 37 Neutrons 48
Classification Alkali Metal State Solid
Density 1.532 g/cm3 Period/Group 5 / 1
Electronegativity 0.82 Atomic Radius 248 pm
# of Isotopes 2 Color silvery-white
Energy Levels 5 Crystal Structure cubic
Rubidium was discovered in 1861 by Robert Bunsen and Gustav Kirchloff.  

Uses - photocells, catalysts, making special glasses

 

Strontium                     multicolored.gif (1741 bytes)  Click here to return to periodic table              

Symbol Sr Name Strontium
Atomic Number 38 Atomic Mass 87.62 amu
Melting Point 769°C Boiling Point 1384°C
Protons/Electrons 38 Neutrons 50
Classification Alkaline Earth Metal State Solid
Density 2.54 g/cm3 Period/Group 5 / 2
Electronegativity 0.95 Atomic Radius 215 pm
# of Isotopes 4 Color silvery
Energy Levels 5 Crystal Structure hexagonal
Strontium was discovered in 1787 by William Cruikshank.                              

Uses - red flame in fireworks, flares, production of color television tubes, refining zinc, optical materials

 

Yttrium                           multicolored.gif (1741 bytes)  Click here to return to periodic table           

Symbol Y Name Yttrium
Atomic Number 39 Atomic Mass 88.905 amu
Melting Point 152.3°C Boiling Point 3337°C
Protons/Electrons 39 Neutrons 50
Classification Transition Metal State Solid
Density 4.457 g/cm3 Period/Group 5 / 3
Electronegativity 1.22 Atomic Radius 180 pm
# of Isotopes 1 Color silvery
Energy Levels 5 Crystal Structure hexagonal
Yttrium was discovered in 1794 by Johann Gadolin.                                    

Uses - YAG laser, TV phosphor, production of microwave filters, production of simulated diamonds

 

Zirconium                        multicolored.gif (1741 bytes)  Click here to return to periodic table           

Symbol Zr Name Zirconium
Atomic Number 40 Atomic Mass 91.224 amu
Melting Point 1852°C Boiling Point 3578°C
Protons/Electrons 40 Neutrons 51
Classification Transition Metal State Solid
Density 6.49 g/cm3 Period/Group 5 / 4
Electronegativity 1.33 Atomic Radius 160 pm
# of Isotopes 5 Color grayish-white
Energy Levels 5 Crystal Structure hexagonal
Zirconium was discovered in 1789 by Martin Klaproth.                                     

Uses - deoderants, fuel rod clad, laboratory crucibles

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