General Chemistry: Protons and Atomic Mass
Protons and Atomic Mass
Protons have a mass of approximately one atomic mass unit (amu).
The atomic number (Z) of an element is defined as the number of protons in an atom of that element. This
number uniquely identifies each element.
For instance, oxygen has an atomic number of 8 (indicating it has 8 protons), while gadolinium has an atomic
number of 64.
Isotopes and Atomic Weight
Although all atoms of a given element share the same atomic number, they may not have the same mass due to
the presence of isotopes—variants of elements with differing numbers of neutrons.
An example provided below is potassium (K), which has an atomic number of 19 and an approximate atomic
weight of 39.1.
19
K
39.1
Neutrons
Neutrons are neutral particles found in the nucleus alongside protons; they carry no charge.
The mass of a neutron is slightly larger than that of a proton.
Together, protons and neutrons account for nearly all the mass of an atom.
Conclusion Understanding these fundamental components—protons, neutrons, and their roles in defining elements
—is crucial for grasping basic concepts in chemistry and atomic physics.
Mass Number (A) Every atom has a characteristic mass number (A), which is defined as the total count of protons
and neutrons present in the nucleus of the atom.
Atomic Number and Isotopes While all atoms of a specific element maintain the same atomic number (the number
of protons), they can possess different numbers of neutrons. This variability leads to differences in mass number
among atoms of the same element. Atoms that have identical atomic numbers but differing mass numbers are
classified as isotopes.
Example: Carbon Isotopes For instance, carbon has three naturally occurring isotopes:
Carbon-12 (^12C) with 6 protons and 6 neutrons,
Carbon-13 (^13C) with 6 protons and 7 neutrons,
Carbon-14 (^14C) with 6 protons and 8 neutrons.
Protons and Atomic Mass
Protons have a mass of approximately one atomic mass unit (amu).
The atomic number (Z) of an element is defined as the number of protons in an atom of that element. This
number uniquely identifies each element.
For instance, oxygen has an atomic number of 8 (indicating it has 8 protons), while gadolinium has an atomic
number of 64.
Isotopes and Atomic Weight
Although all atoms of a given element share the same atomic number, they may not have the same mass due to
the presence of isotopes—variants of elements with differing numbers of neutrons.
An example provided below is potassium (K), which has an atomic number of 19 and an approximate atomic
weight of 39.1.
19
K
39.1
Neutrons
Neutrons are neutral particles found in the nucleus alongside protons; they carry no charge.
The mass of a neutron is slightly larger than that of a proton.
Together, protons and neutrons account for nearly all the mass of an atom.
Conclusion Understanding these fundamental components—protons, neutrons, and their roles in defining elements
—is crucial for grasping basic concepts in chemistry and atomic physics.
Mass Number (A) Every atom has a characteristic mass number (A), which is defined as the total count of protons
and neutrons present in the nucleus of the atom.
Atomic Number and Isotopes While all atoms of a specific element maintain the same atomic number (the number
of protons), they can possess different numbers of neutrons. This variability leads to differences in mass number
among atoms of the same element. Atoms that have identical atomic numbers but differing mass numbers are
classified as isotopes.
Example: Carbon Isotopes For instance, carbon has three naturally occurring isotopes:
Carbon-12 (^12C) with 6 protons and 6 neutrons,
Carbon-13 (^13C) with 6 protons and 7 neutrons,
Carbon-14 (^14C) with 6 protons and 8 neutrons.
