Matter & Energy


Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Alphabetic list of Chemical Elements (Q-R-S)

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Name: Radium
Symbol: Ra
Atomic Number: 88
Atomic Weight: (226)
Group: Alkaline earth metals
Date Discovered: 1898
Discovered By: Marie Curie

Name: Radon
Symbol: Rn
Atomic Number: 86
Atomic Weight: (222)
Group: Noble gases
Date Discovered: 1900
Discovered By: Friedrich Dorn

Name: Rhenium
Symbol: Re
Atomic Number: 75
Atomic Weight: 186.207
Group: Transition metals
Date Discovered: 1925
Discovered By: Walter Noddack, Ida Tacke, and Otto Berg

Name: Rhodium
Symbol: Rh
Atomic Number: 45
Atomic Weight: 102.9055
Group: Transition metals
Date Discovered: 1804
Discovered By: William Wollaston

Name: Rubidium
Symbol: Rb
Atomic Number: 37
Atomic Weight: 85.4678
Group: Alkali metals
Date Discovered: 1861
Discovered By: Robert Bunsen and Gustav Kirchhoff

Name: Ruthenium
Symbol: Ru
Atomic Number: 44
Atomic Weight: 101.07
Group: Transition metals
Date Discovered: 1827
Discovered By: G. W. Osann (isolated by Karl Klaus 1844)

Name: Rutherfordium
Symbol: Rf
Atomic Number: 104
Atomic Weight: (261)
Group: Transition metals
Date Discovered: 1969
Discovered By: claimed by U.S. scientist Albert Ghiorso and coworkers (disputed by Soviet workers)

Name: Samarium
Symbol: Sm
Atomic Number: 62
Atomic Weight: 150.36
Group: Lanthanide
Date Discovered: series 1879
Discovered By: Paul Lecoq de Boisbaudran

Name: Scandium
Symbol: Sc
Atomic Number: 21
Atomic Weight: 44.9559
Group: Transition metals
Date Discovered: 1876
Discovered By: Lars Nilson

Name: Seaborgium
Symbol: Sg
Atomic Number: 106
Atomic Weight: (266)
Group: Transition metals
Date Discovered: 1974
Discovered By: claimed by Georgii Flerov and coworkers, and independently by Albert Ghiorso and coworkers

Name: Selenium
Symbol: Se
Atomic Number: 34
Atomic Weight: 78.96
Group: Nonmetals
Date Discovered: 1817
Discovered By: Jöns Berzelius

Name: Silicon
Symbol: Si
Atomic Number: 14
Atomic Weight: 28.0855
Group: Nonmetals
Date Discovered: 1823
Discovered By: Johan Arfwedson

Name: Silver
Symbol: Ag
Atomic Number: 47
Atomic Weight: 107.8682
Group: Transition metals
Date Discovered: prehistoric
Discovered By: unknown

Name: Sodium
Symbol: Na
Atomic Number: 11
Atomic Weight: 22.9898
Group: Alkali metals
Date Discovered: 1807
Discovered By: Humphry Davy

Name: Strontium
Symbol: Sr
Atomic Number: 38
Atomic Weight: 87.62
Group: Alkaline earth metals
Date Discovered: 1808
Discovered By: Humphry Davy

Name: Sulfur
Symbol: S
Atomic Number: 16
Atomic Weight: 32.067
Group: Nonmetals
Date Discovered: prehistoric
Discovered By: unknown