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 (I-J-K-L-M)

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Name: Indium
Symbol: In
Atomic Number: 49
Atomic Weight: 114.818
Group: Other metals
Date Discovered: 1863
Discovered By: Ferdinand Reich and Hieronymus Richter

Name: Iodine
Symbol: I
Atomic Number: 53
Atomic Weight: 126.9045
Group: Halogens
Date Discovered: 1811
Discovered By: Bernard Courtois

Name: Iridium
Symbol: Ir
Atomic Number: 77
Atomic Weight: 192.217
Group: Transition metals
Date Discovered: 1804
Discovered By: Smithson Tennant

Name: Iron
Symbol: Fe
Atomic Number: 26
Atomic Weight: 55.845
Group: Transition metals
Date Discovered: prehistoric
Discovered By: unknown

Name: Krypton
Symbol: Kr
Atomic Number: 36
Atomic Weight: 83.798
Group: Noble gases
Date Discovered: 1898
Discovered By: William Ramsay and Morris Travers

Name: Lanthanum
Symbol: La
Atomic Number: 57
Atomic Weight: 138.9055
Group: Lanthanide
Date Discovered: series 1839
Discovered By: Carl Mosander

Name: Lawrencium
Symbol: Lr
Atomic Number: 103
Atomic Weight: (260)
Group: Transition metals
Date Discovered: 1961
Discovered By: Albert Ghiorso, Torbjørn Sikkeland, Almon Larsh, and Robert Latimer

Name: Lead
Symbol: Pb
Atomic Number: 82
Atomic Weight: 207.2
Group: Other metals
Date Discovered: prehistoric
Discovered By: unknown

Name: Lithium
Symbol: Li
Atomic Number: 3
Atomic Weight: 6.941
Group: Alkali metals
Date Discovered: 1817
Discovered By: Johan Arfwedson

Name: Lutetium
Symbol: Lu
Atomic Number: 71
Atomic Weight: 174.967
Group: Transition metals
Date Discovered: 1907
Discovered By: Georges Urbain and Carl von Welsbach, independently of each other

Name: Magnesium
Symbol: Mg
Atomic Number: 12
Atomic Weight: 24.3051
Group: Alkaline earth metals
Date Discovered: 1755
Discovered By: Joseph Black (oxide isolated by Humphry Davy 1808; pure form isolated by Antoine-Alexandre-Brutus Bussy 1828)

Name: Manganese
Symbol: Mn
Atomic Number: 25
Atomic Weight: 54.938
Group: Transition metals
Date Discovered: 1774
Discovered By: Johann Gottlieb Gahn

Name: Meitnerium
Symbol: Mt
Atomic Number: 109
Atomic Weight: (268)
Group: Transition metals
Date Discovered: 1982
Discovered By: Peter Armbruster and coworkers

Name: Mendelevium
Symbol: Md
Atomic Number: 101
Atomic Weight: (258)
Group: Actinide
Date Discovered: series 1955
Discovered By: Albert Ghiorso, Bernard G. Harvey, Gregory Choppin, Stanley Thompson, and Glenn Seaborg

Name: Mercury
Symbol: Hg
Atomic Number: 80
Atomic Weight: 200.59
Group: Transition metals
Date Discovered: prehistoric
Discovered By: unknown

Name: Molybdenum
Symbol: Mo
Atomic Number: 42
Atomic Weight: 95.94
Group: Transition metals
Date Discovered: 1781
Discovered By: named by Karl Scheele (isolated by Peter Jacob Hjelm 1782)