Astrophysics (index)about

Element

(Chemical Element)
(class of atom based on its number of protons)

An Element (Chemical Element) is a class of atoms consisting of those with a specific number of protons, i.e., atoms with 10 protons make up one element, those with 11 make up another. Currently, 118 elements have been discovered or created. The proton count is termed its Atomic Number (Z). Two atoms may be of the same element even if their number of neutrons differs, in which case they are termed different Isotopes of the same element.

The total number of nucleons (protons and neutrons in the nucleus) is termed the Mass Number or Atomic Mass Number, so two isotopes of the same element will have the same atomic number but differ in mass numbers. The term Atomic Weight (or Relative Atomic Mass) is the average mass per atom in Daltons (1/12 of Carbon-12, carbon with mass number 12) in a sample of the element. (Atomic Weight is the traditional term but the latter term is more reasonable since it is a measure of mass rather than weight.) The atomic weight reflects the relative Abundances of the isotopes in the sample. The term Standard Atomic Weight is used for the known atomic weight of an element as found on Earth, i.e., reflecting abundances on Earth.

Example elements:

NameSymbolAtomic Number
HydrogenH1
HeliumHe2
LithiumLi3
BerylliumBe4
CarbonC6
NitrogenN7
OxygenO8
NeonNe8
FluorineF9
SodiumNa11
MagnesiumMg12
AluminumAl13
SiliconSi14
PhosphorusP15
SulfurS16
ChlorineCl17
PotassiumK19
CalciumCl20
ChromiumCr24
IronFe26
NickelNi28
GermaniumGe32
StrontiumSr38
ZirconiumZi40
XenonXe54
BariumBa56
PraseodymiumPr59
NeodymiumNd60
EuropiumEu63
IridiumIr77
PlatinumPt78

(physics,chemistry)
http://en.wikipedia.org/wiki/Chemical_element

Referenced by:
Absorption Line
Abundances
Alpha Element
Alpha Process
Big Bang Nucleosynthesis (BBN)
Beta Decay
Calcium (Ca)
Carbon (C)
Chemodynamics
Double-Line Spectroscopic Binary
Electron Capture
Equilibrium Condensation Model
Fusion
Globular Cluster (GC)
Helium (He)
HI Region (HI)
Hydrocarbon (HC)
Hydrogen (H)
Ice Giant
Iron (Fe)
Iron Peak
Isotope
Lithium (Li)
Mass Fraction
Metal
Metallicity (Z)
Molecular Handedness
Neutron Scattering
Neutron Spectrometer
Nickel (Ni)
Nitrogen (N)
Nucleosynthesis
Oxygen (O)
Photoionization
Post Main Sequence Star
Radioactive Dating
Radioactive Decay
Refractory Material
R-Process
Siderophile
Silicon (Si)
Spectral Line Energy Distribution (SLED)
Sodium (Na)
Solar and Heliospheric Observatory (SOHO)
Spectral Line
S-Process
Stellar Age Determination
Stellar Model Atmosphere
Sulfur (S)
Surface Abundance
Trans-Iron Element
Type Ia Supernova
Valley of Beta Stability
Z+

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