2.1.1 Atomic structure and isotopes

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13 Terms

1
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What is the definition of relative isotopic mass?

The mass of an atom of an isotope compared with 1/12 of the mass of an atom of carbon-12.

2
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What is the definition of isotopes?

Atoms of the same element with different numbers of neutrons and so, different masses.

3
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What is the definition of 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.

4
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What does it mean by ‘the weighted mean mass’ in relative atomic mass?

It takes account the abundance of different isotopes for an element, giving a more accurate average of atomic mass.

5
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What is the relative mass and relative charge of a proton?

Relative mass = 1

Relative charge = +1

6
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What is the relative mass and relative charge of a neutron?

Relative mass = 1

Relative charge = 0

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What is the relative mass and relative charge of a electron?

Relative mass = 1/1836

Relative charge = -1

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What are the uses of mass spectrometry?

  • To find the relative isotopic masses and the relative abundances of the isotope

(abundance tells us how common each isotope is)

<ul><li><p>To find the relative isotopic masses and the relative abundances of the isotope</p></li></ul><p>(abundance tells us how common each isotope is)</p>
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How do you interpret the mass spectra to find the relative atomic mass?

The symbol m/z means mass/charge.

The 3 key characteristics:

  1. The number of peaks shows how many isotopes there are.

  2. The m/z value of each peak shows the isotope mass (because the charge of the ion is +1, so everything divided by 1 is that number).

  3. The height of each peak shows the relative abundance of that isotope.

<p>The symbol m/z means mass/charge.</p><p>The 3 key characteristics:</p><ol><li><p>The <strong>number of peaks </strong>shows how many isotopes there are.</p></li><li><p>The <strong>m/z value of each peak</strong> shows the isotope mass (because the charge of the ion is +1, so everything divided by 1 is that number).</p></li><li><p>The <strong>height of each peak</strong> shows the relative abundance of that isotope. </p></li></ol>
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What is the formula to find the relative atomic mass (RAM) ?

The sum of (each relative isotopic mass x its abundance) divided by the total abundance (usually 100)

<p>The sum of (each relative isotopic mass x its abundance) divided by the total abundance (usually 100)</p>
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What is the definition of relative molecular mass (Mr) ?

The weighted mean mass of a molecule of a compound compared with 1/12 of the mass of an atom of carbon-12.

  • Used for simple covalent substances

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What is the definition of relative formula mass?

The weighted mean mass of the formula unit of a compound compared with 1/12 of the mass of an atom of carbon-12.

  • used for ionic substances

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Why is the carbon-12 isotope chosen as the international standard?

Because it can be obtained in an isotopically pure state and is unreactive.