# Atomic Masses

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• Created by: racheon
• Created on: 28-01-14 20:08
What do we use to compare masses of different atoms?
Relative mass.
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What has been chosen as the measurement of relative mass?
The carbon-12 isotope.
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What unit is used to measure atomic masses?
Unified atomic mass.
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How heavy is 1u?
1.6605 x 10^-27kg.
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What is the mass of a carbon-12 atom?
12u.
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What is 1/12th of a carbon-12 atom?
1u.
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Define relative isotopic mass.
The mass of an atom of an isotope compared with 1/12 of the mass of an atom of carbon-12.
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Are all atoms in an isotope identical?
Yes.
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For an isotope, what is the relative atomic mass the same as?
The mass number.
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What have we neglected when talking about relative masses?
Electrons' mass.
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What do the masses of a proton and neutron equal?
1u.
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Define relative atomic mass.
The weighted mean mass of an atom of an element compared with 1/12 of the mass of an atom of carbon-12.
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Define weighted mean mass.
The contribution made by each isotope to the overall mass of an element.
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What does the contribution of an isotope depend on? (2)
The percentage of the isotope and the relative mass of the isotope.
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Define relative molecular mass.
The weighted mean mass of a molecule compared with 1/12 of the mass of an atom of carbon-12.
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What is relative molecular mass used for?
It's used to work out simple molecules.
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How do you work out a relative molecular mass?
By adding together the relative atomic masses of each atom.
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Define relative formula mass.
The weighted mean mass of a formula unit compared with 1/12 of the mass of an atom of carbon-12.
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What is relative formula mass used to work out? (2)
Giant structures and covalent compounds.
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How do you work out a relative formula mass?
By adding together the relative atomic masses of each atom.
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## Other cards in this set

### Card 2

#### Front

What has been chosen as the measurement of relative mass?

#### Back

The carbon-12 isotope.

### Card 3

#### Front

What unit is used to measure atomic masses?

How heavy is 1u?

### Card 5

#### Front

What is the mass of a carbon-12 atom?