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(73.8% natural abundance). The number 46, 47 and so on are the total numbers of protons and

neutrons. Because of atomic number of each element is fixed, the number of neutrons can be
calculated by subtracting protons number. For example, Ti consists 24 neutrons when 46
46
mines 22 is equal 24. Furthermore, the protons number is determines how many electrons
surround the nucleus, and it is the arrangement of these electrons that determines most of the
chemical behavior of an element.

Figure 2.2: Carbon and Aluminum atom

Atomic mass

Together, the number of protons and the number of neutrons determine an

element’s mass number: mass number = protons + neutrons. Mass number also called atomic

mass. A property closely related to an atom’s mass number is its atomic mass. The atomic
mass of a single atom is simply its total mass and is typically expressed in atomic mass units

or amu. By definition, an atom of carbon with six neutrons, carbon-12, has an atomic mass of

12 amu. In general, though, an atom's atomic mass will be very close to its mass number but

will have some deviation in the decimal places. Since an element’s isotopes have different

atomic masses, scientists may also determine the relative atomic mass or also called
the atomic weight for an element. The relative atomic mass is an average of the atomic masses

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