Mass Number Chemistry Example 1

Follow the full solution, then compare it with the other examples linked below.

Example 1

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

Solution

  1. 1
    Mass number A=protons+neutrons=17+18=35A = \text{protons} + \text{neutrons} = 17 + 18 = 35.
  2. 2
    Atomic number Z=17Z = 17 corresponds to chlorine (Cl).
  3. 3
    This isotope is written as 1735Cl{}^{35}_{17}\text{Cl}.

Answer

A=35, Chlorine-35A = 35,\text{ Chlorine-35}
The mass number is the total number of nucleons (protons + neutrons) in the nucleus. It is always a whole number and appears as a superscript in isotope notation.

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 2 medium

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

Example 3 medium

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

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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