Atomic Number
Definition and meaning of Atomic Number in chemistry.
Atomic number is the number of protons in the nucleus of an atom, which uniquely identifies each chemical element. Represented by the symbol Z, it determines the element's position on the periodic table and its chemical properties.
In more detail
In a neutral atom, the atomic number equals the number of electrons surrounding the nucleus, since atoms have equal numbers of positively charged protons and negatively charged electrons. The atomic number is constant for a given element: all hydrogen atoms have atomic number 1, all carbon atoms have atomic number 6, and all oxygen atoms have atomic number 8. Isotopes of the same element have identical atomic numbers but differ in their number of neutrons and thus their mass numbers. Elements are arranged on the periodic table in order of increasing atomic number, which is the primary organizing principle of the periodic table.
Key facts
| Symbol | Z |
|---|---|
| Definition | Number of protons in an atom's nucleus |
| Field | General Chemistry |
| Periodic Table | Elements arranged by increasing atomic number |
Hydrogen has atomic number 1 (containing 1 proton), carbon has atomic number 6 (containing 6 protons), and oxygen has atomic number 8 (containing 8 protons). Uranium-238 and Uranium-235 are both uranium isotopes with atomic number 92 but different mass numbers.
Frequently asked questions
Does atomic number change for different isotopes of the same element?
No. All isotopes of an element have the same atomic number. They differ only in the number of neutrons and thus their mass number.
Why is atomic number important?
Atomic number uniquely identifies an element and determines its chemical properties, electron configuration, and position on the periodic table.