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The 174 pages that link to Atomic number, each with the reason it gives.

• Periodic tableRelated: Increasing atomic number sets the table's ordering principle.

• IsotopeRelated: Isotopes of one element all have the same atomic number.

• Chemical elementRelated: It is the defining count that distinguishes one element from every other.

• ProtonRelated: Changing the proton count changes an atom into a different element.

• PotassiumNarrower topic: Potassium’s 19 protons define it as element 19.

• ChlorineRelated: Chlorine’s 17 protons define it as element 17.

• Atomic nucleusRelated: Proton count gives the nucleus its identity as a particular element.

• CalciumRelated: Calcium’s atomic number, 20, defines its elemental identity.

• SodiumNarrower topic: Sodium’s atomic number, 11, identifies its nucleus and fixes its place in the periodic table.

• OganessonNarrower topic: Oganesson is element 118 because its nucleus contains 118 protons.

• IonRelated: Ion formation changes electron count, not the atomic number.

• Alkali metalRelated: Atomic number distinguishes the successive elements in the alkali-metal group.

• Ionization energyRelated: It sets nuclear charge and helps explain periodic changes in electron binding.

• Superheavy element synthesisNarrower topic: Superheavy elements are defined by their exceptionally high proton counts.

• Dmitri MendeleevRelated: Ordering by atomic number later explained periodicity more accurately than Mendeleev's atomic-weight ordering.

• IodineRelated: Iodine’s atomic number, 53, fixes its identity and nuclear charge.

• Periodic trendsRelated: Increasing atomic number across a period adds nuclear charge one proton at a time.

• HeliumNarrower topic: Helium’s atomic number is two because every helium nucleus contains two protons.

• X-ray fluorescenceRelated: Element identity determines the energies of its characteristic X-ray lines.

• ZincRelated: Zinc’s atomic number is 30.

• ActinideRelated: The series runs through consecutive atomic numbers, from actinium's 89 to lawrencium's 103.

• GoldRelated: Gold’s atomic number, 79, fixes its identity regardless of isotope or charge.

• Uranium-238Related: Its 92 protons identify uranium regardless of neutron count.

• NihoniumRelated: Nihonium is element 113 because its nuclei contain 113 protons.

• Nuclear transmutationRelated: A change in proton count is the defining criterion for transmutation.

• BoronNarrower topic: Boron’s five protons define its place in the periodic table.

• Potassium ionRelated: Potassium’s atomic number is 19, fixing the identity of its ion.

• Mass numberRelated: Together with mass number, it specifies a nuclide’s neutron count.

• NuclideRelated: Nuclides with the same atomic number belong to the same element.

• Periodic lawRelated: Ordering elements by proton count gives the modern periodic law its organizing variable.

• Sodium ionRelated: Sodium’s 11 protons determine its identity even after it becomes an ion.

• TinNarrower topic: Tin’s atomic number 50 fixes its identity and nuclear charge.

• AtomRelated: It gives each element its defining identity.

• Atomic theoryBroader topic: It gives atomic identity a precise basis within the framework.

• BerylliumNarrower topic: Beryllium’s four protons define its place as element 4.

• Chemical symbolRelated: A symbol identifies an element whose defining property is its atomic number.

• UnunenniumRelated: The defining identity of ununennium is 119 protons.

• AnionRelated: Gaining electrons changes charge, not the atomic number or element.

• Effective nuclear chargeRelated: It sets the unscreened nuclear charge from which effective charge is estimated.

• Element discoveryNarrower topic: A new element is defined by a proton number not previously confirmed.

• Relativistic effectRelated: Larger nuclear charge draws inner electrons faster, making relativistic effects stronger in heavy atoms.

• Transuranium elementNarrower topic: The boundary is exact: transuranium elements have atomic numbers above 92.

• Cahn–Ingold–Prelog priority rulesRelated: The first point of comparison when attached atoms differ.

• E–Z notationRelated: When directly attached atoms differ, the higher atomic number gives the higher substituent priority.

• Rutherford scatteringRelated: The scattering strength depends on the target nucleus’s positive charge, indexed by atomic number.

• Transactinide elementNarrower topic: The boundary is defined directly: transactinides have atomic numbers above 103.

• IsobarRelated: Isobars differ in this number.

• MoscoviumRelated: Moscovium is element 115 because each of its nuclei contains 115 protons.

• TennessineNarrower topic: Tennessine is element 117 because its nuclei contain 117 protons.

• UnbiniliumNarrower topic: Element 120 would have 120 protons, fixing its place beyond oganesson.