Astrophysics (Index)About

element

(chemical element)
(class of atom based on its number of protons)

The chemistry term element (chemical element) consists of all material that cannot be (chemically) changed or broken down into other materials. Such an element consists of all atoms with some given number of protons, i.e., all atoms with 10 protons comprise one particular element and those with 11 comprise 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 atomic 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 the mass of carbon with mass number 12, i.e., of carbon-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 such abundances on Earth. Example elements:

NameSymbolAtomic Number
hydrogenH1
heliumHe2
lithiumLi3
berylliumBe4
boronB5
carbonC6
nitrogenN7
oxygenO8
fluorineF9
neonNe10
sodiumNa11
magnesiumMg12
aluminumAl13
siliconSi14
phosphorusP15
sulfurS16
chlorineCl17
argonAr18
potassiumK19
calciumCa20
scandiumSc21
titaniumTi22
vanadiumV23
chromiumCr24
manganeseMn25
ironFe26
cobaltCo27
nickelNi28
copperCu29
zincZn30
germaniumGe32
strontiumSr38
zirconiumZr40
technetiumTc43
silverAg47
telluriumTe52
xenonXe54
cesiumCs55
bariumBa56
lanthanumLa57
praseodymiumPr59
neodymiumNd60
europiumEu63
iridiumIr77
platinumPt78
goldAu79
mercuryHg80
thalliumTl81
leadPb82
bismuthBi83
radiumRa88
actiniumAc89
thoriumTh90
uraniumU92
plutoniumPu94

(physics,chemistry)
Further reading:
https://en.wikipedia.org/wiki/Chemical_element
https://en.wikipedia.org/wiki/List_of_chemical_elements
https://www.thoughtco.com/what-is-a-chemical-element-604297
https://www.oxfordreference.com/display/10.1093/oi/authority.20110803095605316
https://www.windows2universe.org/physical_science/element.html
https://www.chemeurope.com/en/encyclopedia/Chemical_element.html

Referenced by pages:
absorption line
abundances
alpha element
alpha process (α process)
alpha-enhanced
aluminum (Al)
astrobiology
atomic number (Z)
Avogadro's number (NA)
barium star (Ba star)
Big Bang nucleosynthesis (BBN)
bracket notation
calcium (Ca)
carbon (C)
carbon burning
chemical equilibrium (CE)
Compton reflection
cosmic dust
cosmic neutrino background (CNB)
Cryogenic Dark Matter Search (CDMS)
double-line spectroscopic binary (SB2)
electron capture
electron shell
emission line
equilibrium condensation model
fine structure
fusion
globular cluster (GC)
GW170817
helium (He)
HI region (HI)
Honda-like star
hydrocarbon (HC)
hydrogen (H)
hydrogen cyanide (HCN)
ice giant
ionization correction factor (ICF)
iron (Fe)
iron peak
iron peak element
isotope
Lambda Boötis star (λ Boo)
lanthanide (Ln)
light curve
lithium (Li)
lithium depletion boundary (LDB)
Lyman series (L)
magnesium (Mg)
mass fraction
mass number (A)
metal
metallic hydrogen
metallicity (Z)
mole (mol)
molecular handedness
neon (Ne)
neutron rich
neutron scattering
neutron spectrometer
nickel (Ni)
nitrogen (N)
nuclear statistical equilibrium (NSE)
nucleosynthesis
nuclide
oxidation state
oxygen (O)
phosphorus (P)
photoionization
post-main-sequence star
potassium/thorium ratio (K/Th ratio)
proton
r-process
radioactive dating
radioactive decay
radioactivity
radiolysis
reducing atmosphere
refractory material
rocky planet
Rydberg constant (RH)
s-process
sedimentation
self-absorption
sensitivity function (S)
siderophile
silicon (Si)
silicon burning
SMSS J2003-1142
sodium (Na)
Solar and Heliospheric Observatory (SOHO)
spectral line
spectral line designation
spectral line energy distribution (SLED)
spectral type
stellar age determination
stellar model atmosphere
sulfur (S)
supernova light curve (SN light curve)
surface abundance
technetium star
titanium (Ti)
trans-iron element
transition region
Type Ia supernova
valley of beta stability
volatile material
Z+
ZEPLIN

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