The Atomic Mass Of An Element Is

How do you determine the atomic mass of an element?

  • The atomic mass of an element is the weighted average mass of the atoms in a naturally occurring sample of the element. A weighted average mass reflects both the mass and the relative abundance of the isotopes as they occur in nature.
  • Atomic Mass - Atomic mass is the mass of an atom or other particle, expressed in unified atomic mass units (u). An atomic mass unit is defined as 1/12th the mass of a carbon-12 atom. Since the mass of electrons is much smaller than that of protons and neutrons, the atomic mass is nearly identical to the mass number.

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2 Answers

The Atomic Mass Of An Element Is

The Atomic Mass Of An Element Is The Sum

I can think of only two good ways to determine the atomic mass of an element.


Most naturally-occurring elements consist of mixtures of isotopes, so you can't just add the masses of the protons and neutrons in a single atom.

1. The easy way Tunnelblick iphone se.

The Atomic Mass Of An Element Is What

Look up the atomic mass in the Periodic Table.

(Adapted from

For example, the atomic mass of Cl is 35.45 u.

2. The harder way

Take the weighted average of the atomic masses of the element's isotopes.

In a weighted average, we multiply each value by a number representing its relative importance (its percentage as a decimal fraction).

The Atomic Mass Of An Element Is Determined By

For example, chlorine consists of 75.78 % chlorine-35 (atomic mass 34.97 u) and 24.22 % chlorine-37 (atomic mass 36.97 u)

#bb'Atomic Mass/u' color(white)(m)bb'Fractional abundance' color(white)(m)bb'Contribution/u'#
#color(white)(mml)34.97color(white)(mmmmmmmmm) 0.7578color(white)(mmmmmmmmm) 26.50#
#color(white)(mmmmmmmmmmmmmmmm)'Atomic mass = ' color(white)(mll) stackrel(———)(35.45)#

The atomic mass of chlorine is 35.45 u.


To find the molar mass of an element,
all you need to have is a periodic table.

The molar mass is the same thing as the atomic mass on the periodic table.

For example, let's look at Chromium. (Image below)

You can identify the atomic mass right away, 52.
Therefore, the molar mass of Chromium is #52 g mol^-1#

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