Atomic Structure and Mass Spectrometry

Flashcards covering atomic structure definitions, isotope calculations, and the components and functions of a mass spectrometer based on the lecture notes.

What is the definition of Atomic Number ($Z$)?

The number of protons in the nucleus of an atom.

What is the definition of Mass Number ($A$)?

The sum of the protons and neutrons (also known as the Nucleon Number) in the nucleus.

How is Relative Atomic Mass ($A_r$) defined?

The mass of an atom relative to the $^{12}C$ isotope having a value of $12.000$.

What is the formula for Relative Atomic Mass ($A_r$)?

$$A_r = \frac{\text{average mass per atom of an element} \times 12}{\text{mass of one atom of carbon-12}}$$

Which relative mass term is specifically used for the formula of a species or ion, such as $NaCl$ or $OH^-$?

Relative Formula Mass.

What are the two definitions provided for isotopes?

Atoms with the same atomic number but different mass number, or the same number of protons but different numbers of neutrons.

Why are the chemical properties of isotopes of the same element identical?

Chemical properties are identical because they have the same number of protons and electrons.

What did the mass spectrograph reveal about atoms of the same element that explained non-whole number relative atomic masses?

It revealed that atoms of the same element could have different masses due to the variation in the number of neutrons in the nucleus.

Using the transcript's example, calculate the average relative atomic mass of chlorine if $75\%$ is $^{35}Cl$ and $25\%$ is $^{37}Cl$.

$$\frac{(75 \times 35) + (25 \times 37)}{100} = 35.5$$

Who used mass spectra to demonstrate that naturally occurring neon consists of three isotopes, and in what year did he win the Nobel Prize?

Aston; 1922.

What are the three isotopes of neon identified in the lecture?

$^{20}Ne$, $^{21}Ne$, and $^{22}Ne$.

In a mass spectrum, what information do the positions of the peaks and the peak intensities provide?

The positions of peaks give the atomic mass ($m/z$), and the peak intensity gives the relative abundance.

What is the calculated average relative atomic mass of neon based on the abundances $90.92\%$ of $^{20}Ne$, $0.26\%$ of $^{21}Ne$, and $8.82\%$ of $^{22}Ne$?

$$20.18$$

What are the three main components of a mass spectrometer?

The ion source, the analyser, and the detector.

What occurs in the ion source of a mass spectrometer?

Gaseous atoms are bombarded by electrons from a gun to be ionised, usually to a $1+$ charge, and then accelerated by an electric field.

On what factor does the radius of the path within the analyser depend?

The value of the mass/charge ratio ($m/z$).

How does the path of a heavier isotope in the analyser compare to a lighter one?

Ions of heavier isotopes with larger $m/z$ values follow a larger radius curve.

What happens to the $m/z$ value and the abundance of an ion if it acquires a $2+$ charge instead of a $1+$ charge?

The $m/z$ value is halved, but the abundance remains the same.

According to the isotopes table, what is the symbol and charge for species G which has $16$ protons, $16$ neutrons, and $18$ electrons?

$$^{32}S^{2-}$$

Identify the symbol and charge for species H, which contains $13$ protons, $14$ neutrons, and $10$ electrons.

$$^{27}Al^{3+}$$

Based on the Potassium-39 and Potassium-41 example, if the average mass is $39.1$, what is the percentage of $^{39}K$?

$$95\%$$

What are the two common detection methods used in the detector stage of a mass spectrometer?

Electric or photographic detection methods.