Mass Number Chemistry Example 3

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Example 3

medium
An isotope has 26 protons and 30 neutrons. What is its mass number? Identify the element.

Solution

  1. 1
    The mass number AA is the total number of protons and neutrons (collectively called nucleons) in the nucleus: A=Z+NA = Z + N.
  2. 2
    Substitute the given values: A=26+30=56A = 26 + 30 = 56.
  3. 3
    The number of protons (Z=26Z = 26) determines the element. Looking up Z=26Z = 26 on the periodic table: this is **iron (Fe)**. The isotope is written as 56Fe{}^{56}\text{Fe}.

Answer

Mass number A=56A = 56. The element is iron (56Fe{}^{56}\text{Fe}).
The mass number equals protons plus neutrons, while the atomic number (number of protons) uniquely identifies the element. Iron-56 is the most common and most stable isotope of iron, making up about 91.7% of naturally occurring iron.

About Mass Number

The total count of protons and neutrons (collectively called nucleons) in an atom's nucleus, always a whole number, used to identify specific isotopes of an.

Learn more about Mass Number →

More Mass Number Examples

Example 1 easy

An atom has 17 protons and 18 neutrons. What is its mass number and what element is it?

Example 2 medium

Why is the atomic mass of chlorine listed as [formula] amu on the periodic table, rather than a whol

Example 4 easy

Find the mass number of an atom with 26 protons and 30 neutrons.

Example 5 easy

An atom has 17 protons and 18 neutrons. What is its mass number?

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