# T/F: The mass of an atom is so small it is rounded to 0 amu?

### 5 Answers

- Dr WLv 74 weeks ago
FALSE

some things you need to know..

.. (1) 1 amu = 1/6.022x10^23 grams = 1.66x10^-24 grams

.. (2) the mass of 1 proton ~ 1 amu

.. (3) all atoms have at least 1 proton

therefore

.. all atoms have mass ≿ 1 amu

.. the mass of an atom is never rounded to 0 amu.

- ChemTeamLv 74 weeks ago
This is a false statement.

amu is not the same as mass. mass is measured in grams while amu is the unit for a concept called 'relative atomic mass.

The basic definition is this: the carbon-12 isotope (6 proton & 6 neutron) is _defined_ as weighing exactly 12 amu.

If you are some other element and your nucleus weighs exactly twice what C-12 weighs, then you weigh 24 amu.

The selection of C-12 as the standard for amu occurred in 1957, I think.

You can determine the mass of 1 amu and I do not have it memorized. In all my years of classroom teaching, I never bothered with what 1 amu weighed in grams. There are problems that do use that relationship, I never bothered with them.

By the way, the standard for g (more exactly, kg) is a cylinder of 90% platinum and 10% iridium, I think. It is defined was weighing 1000 g. There is only one primary standard (kept in Paris) and it has been brought out 4 times since 1900 to help calibrate some secondary standards.

- UserLv 74 weeks ago
...of an atom of what?

Hydrogen - lightest atom - average mass of one atom = 1.008 AMU

Uranium - heaviest stable naturally-occuring atom - average mass of one atom = 238.03 AMU

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