Atomic Structure

Question 1

What’s the symbol for atomic number?

Answer 1

Z

Question 2

What’s the symbol for atomic mass?

Answer 2

A

Question 3

How do isotopes differ in chemical properties?

Answer 3

They don’t

Question 4

For ToF mass spec of atoms, when there are small peaks at lower m/z; why are they there, why is that their m/z value and how big are there peaks and why?

Answer 4

These are 2+ ions of the element in question. There m/z is just half the m/z of their normal isotopes and they have very small peaks because more energy is needed to remove the second electron

Question 5

After 3d, state the order of subshell filling

Answer 5

4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, 8s

Question 6

What’s the ‘valence shell’?

Answer 6

The incomplete outermost shell of an atom

Question 7

What’s the name for ‘the incomplete outermost shell of an atom’?

Answer 7

The valence shell

Question 8

What’s the shell of an atom?

Answer 8

The area around the nucleus where electrons orbit

Question 9

What’s the name for ‘the area around the nucleus where electrons orbit’?

Answer 9

The shell of an atom

Question 10

What’s a subshell of an atom?

Answer 10

Shells which are divided into smaller shells; s, p, d & f, and are made of orbitals

Question 11

What’s the name for ‘shells which are divided into smaller shells’?

Answer 11

Subshells

Question 12

What’s an orbital?

Answer 12

Regions around the nucleus that can hold up to 2 electrons, making up subshells

Question 13

What’s the name for ‘regions around the nucleus that can hold up to 2 electrons’?

Answer 13

Orbitals

Question 14

What’s electron spin?

Answer 14

A quantum mechanical property of electrons. In an electron pair inside an orbital, if one spins upwards the other must spin downwards, they can’t spin in the same direction

Question 15

What’s the name for the quantum mechanical property of electrons that says that in an electron pair inside an orbital, if one spins upwards the other must spin downwards, they can’t spin in the same direction?

Answer 15

Electron spin

Question 16

Suggest what might cause the relative atomic mass of a sample produced from Mass Spec to be different from the relative atomic mass given in the Periodic Table

Answer 16

Other isotopes present / some isotopes absent / different abundances of
isotopes

Question 17

Write an equation for the reaction that occurs when an ion (M+) hits the detector in Mass Spec

Answer 17

M+ + e(−) -> M
Ignore state symbols
Allow M^2+ + 2e(−) -> M

Question 18

State the m / z value of the ion that produces the biggest current at the detector when the spectrum in the graph is recorded.

Answer 18

Most abundant ion

Question 19

Predict whether the atomic radius of Te-124 is larger than, smaller than or the same as the atomic radius of Te-130. Explain your answer.

Answer 19

Same because each isotope has the same number of protons / same nuclear charge and
same number of electrons / electronic configuration
Ignore more neutrons in Te-130

Question 20

Explain why it is necessary to ionise molecules when measuring their mass in a TOF mass spectrometer

Answer 20

• Ions, not molecules, will interact with and be accelerated by an electric field
• Only ions will create a current when hitting the detector

Question 21

In a mass spectrometer, the isotopes of an element are separated. Two measurements for each isotope are recorded on the mass spectrum. State the two measurements that are recorded for each isotope.

Answer 21

• m/z ratio
• Relative Abundance

Question 22

Define the term relative atomic mass

Answer 22

Average mass of 1 atom of an element compared to 1/12th mass of one atom of 12C

Question 23

When given a mass spectrum with peaks of different abundances at different m/z ratios, which one of the isotopes is deflected the most in the magnetic field of a mass spectrometer? Why?

Answer 23

Pick whichever ion has the lowest m/z ratio because it has the lowest m/z ratio

Question 24

In a mass spectrometer, the relative abundance of each isotope is proportional to the current generated by that isotope at the detector. Explain how this current is generated

Answer 24

Electron(s) transferred / flow at the detector from detector / plate to the (+) ion
Do not allow from a charged plate

Question 25

A sample of ethanedioic acid was treated with an excess of an unknown alcohol in the presence of a strong acid catalyst. The products of the reaction were separated and analysed in a time of flight (TOF) mass spectrometer. Two peaks were observed at m / z = 104 and 118. Identify the species responsible for the two peaks

Answer 25

[CH3OCOCOOH]+ and [CH3OCOCOOCH3]+
Allow names, do not allow molecular formula

Question 26

You’re given 2 species and their m/z. Outline how the TOF mass spectrometer is able to separate these two species to
give two peaks

Answer 26

Positive ions are accelerated by an electric field to a constant kinetic energy. The positive ions with lower m/z have the same kinetic energy as those with
higher m/z yet moves faster. Therefore, ions with lower m/z arrive at the detector first

Question 27

If the mass of a proton, neutron and electron is 1.6725 x 10^-24 g, 1.6748 x 10^-24 g and 0.0009 x 10^-24 g respectively, what’s the mass of a H atom?

Answer 27

1.6734 × 10^−24 g