Astrophysics (Index)About

atomic number

(Z, proton number)
(number of protons in an atomic nucleus)

An element's atomic number (or proton number, typically symbolized as Z) is the number of protons in its nucleus. (An element is defined to be atoms with that element's associated atomic number.) The number of protons determines how many electrons orbit within neutral atom of the element, a major determinant of the element's chemical properties. Chemistry's periodic table of the elements lays them out in the order their atomic numbers, lining them up in columns such that elements in a column tend to have similar chemical properties.

Further reading:

Referenced by pages:
alpha capture
alpha process
beta decay
calcium (Ca)
carbon (C)
electron pressure
Fermi sea
fine structure
helium (He)
hydrogen (H)
iron (Fe)
iron peak
lithium (Li)
lanthanide (Ln)
magnesium (Mg)
neon (Ne)
neutron capture
neutron drip
nickel (Ni)
nitrogen (N)
oxygen (O)
radioactive decay
silicon (Si)
silicon burning
sodium (Na)
sulfur (S)
technetium star
trans-iron element
valley of beta stability