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 (A-B)

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Name: Actinium
Symbol: Ac
Atomic Number: 89
Atomic Weight: (227)
Group: Actinide
Date Discovered: 1899
Discovered By: André Debierne

Name: Aluminum
Symbol: Al
Atomic Number: 13
Atomic Weight: 26.9815
Group: Other metals
Date Discovered: 1824
Discovered By: Hans Oersted (also attributed to Friedrich Wöhler 1827)

Name: Americium
Symbol: Am
Atomic Number: 95
Atomic Weight: 243
Group: Actinide
Date Discovered: 1944
Discovered By: Glenn Seaborg, Ralph James, Leon Morgan, and Albert Ghiorso

Name: Antimony
Symbol: Sb
Atomic Number: 51
Atomic Weight: 121.760
Group: Other metals
Date Discovered: prehistoric
Discovered By: unknown

Name: Argon
Symbol: Ar
Atomic Number: 18
Atomic Weight: 39.948
Group: Noble gases
Date Discovered: 1894
Discovered By: John Rayleigh and William Ramsay

Name: Arsenic
Symbol: As
Atomic Number: 33
Atomic Weight: 74.9216
Group: Nonmetals
Date Discovered: prehistoric
Discovered By: unknown

Name: Astatine
Symbol: At
Atomic Number: 85
Atomic Weight: (210)
Group: Halogens
Date Discovered: 1940
Discovered By: Dale R. Corson, K. R. MacKenzie, and Emilio Segrè

Name: Barium
Symbol: Ba
Atomic Number: 56
Atomic Weight: 137.328
Group: Alkaline earth metals
Date Discovered: 1808
Discovered By: Humphry Davy

Name: Berkelium
Symbol: Bk
Atomic Number: 97
Atomic Weight: (247)
Group: Actinide
Date Discovered: 1949
Discovered By: Glenn Seaborg, Stanley Thompson, and Albert Ghiorso

Name: Beryllium
Symbol: Be
Atomic Number: 4
Atomic Weight: 9.0122
Group: Alkaline earth metals
Date Discovered: 1798
Discovered By: Louis-Nicolas Vauquelin (isolated by Friedrich Wöhler and Antoine-Alexandre-Brutus Bussy 1828)

Name: Bismuth
Symbol: Bi
Atomic Number: 83
Atomic Weight: 208.9804
Group: Other metals
Date Discovered: prehistoric
Discovered By: unknown

Name: Bohrium
Symbol: Bh
Atomic Number: 107
Atomic Weight: (262)
Group: Transition metals
Date Discovered: 1976
Discovered By: Georgii Flerov and Yuri Oganessian (confirmed by German scientist Peter Armbruster and coworkers)

Name: Boron
Symbol: B
Atomic Number: 5
Atomic Weight: 10.81
Group: Nonmetals
Date Discovered: 1808
Discovered By: Humphry Davy, and independently by Joseph Gay-Lussac and Louis-Jacques Thénard

Name: Bromine
Symbol: Br
Atomic Number: 35
Atomic Weight: 79.904
Group: Halogens
Date Discovered: 1826
Discovered By: Antoine-Jérôme Balard