3.1.1 - Atomic Structure

Question 1

What is mass spectrometry?

Answer 1

A method of analysis, which helps us to determine relative atomic masses of unknown substances. It also helps us to determine the abundances of specific isotopes.

Question 2

Outline the 4 steps in TOF mass spectrometry.

Answer 2

1) Ionisation
2) Acceleration
3) Ion Drift
4) Detection

Question 3

What are the two types of ionisation that occur within Time of flight mass spec?

Answer 3

Electrospray Ionisation
Electron Impact

Question 4

Describe the steps involved in ElectroSpray Ionisation.

Answer 4

1) Dissolve the sample in a polar solvent
2) Push it through a tiny nozzle at high pressure
3) Apply a high voltage
4) Each particle will gain a proton
5) The sample will be a gaseous sample of positive ions.

Question 5

Describe Electron Impact Ionisation.

Answer 5

1) Vaporise the sample
2) Sample is bombarded by high energy electrons
3) An electron will be removed from each particle
4) This will create +1 ions.

Question 6

Describe the Acceleration phase of TOF Mass Spec.

Answer 6

The positive ions move through a negative electric field, accelerating toward the negative plate. Lighter ions and ions with a higher charge achieve a higher speed here.

Question 7

Describe Detection in TOF Mass Spec.

Answer 7

Assuming they have the same charge, lighter ions will reach the detector first. When these positive ions hit the detection plate, they gain an electron, producing a flow of charge. The greater the abundance, the greater the current produced.

Question 8

What can happen to molecules during an electron impact ionisation stage?

Answer 8

Molecules will often break up and give a series of peaks caused by the fragments.

Question 9

What do we mean by molecular ion / parent ion?

Answer 9

The largest peak. This is when the complete molecule passes through the mass spectrometer - it has the largest m/z and will be equal to the relative molecular mass.

Question 10

What must we consider when working out Mr from a mass spectra, in which Electrospray Ionisation was used?

Answer 10

The peak will be equal to MH+. To get M, the molecule, we must subtract 1 - the mass of a H+. If the peak is 521.1, their Mr is 520.1.

Question 11

State the order in which sub-shells fill up.

Answer 11

1s - 2s - 2p - 3s - 3p - 4s - 3d - 4p - 5s - 4d - 5p

Question 12

When filling up orbitals, what must you do?

Answer 12

Fill each orbital singly before starting to pair up electrons.

Question 13

What is the shape of a s sub shell?

Answer 13

Spherical.

Question 14

Why does the TOF mass spectrometer need to be under a vacuum?

Answer 14

To prevent air particles ionising and registering on the detector.

Question 15

What are the exceptions to the electronic configuration rule that 4s is filled before 3d?

Answer 15

Chromium (Cr) - 1s2 2s2 2p6 3s2 3p6 4s1 3d5
Copper (Cu) - 1s2 2s2 2p6 3s2 3p6 4s1 3d10.

Question 16

What’s important to note about the electronic structure of d-block ions?

Answer 16

They lose 4s electrons before their 3d electrons.

Question 17

Define first ionisation energy.

Answer 17

The first ionisation energy is the energy required to remove 1 mole of electrons from 1 mole of gaseous atoms.

Question 18

Define second ionisation energy.

Answer 18

The energy required to remove 1 mol of electrons from 1 mole of gaseous ions with a single positive charge.

Question 19

Represent first ionisation energy in an equation.

Answer 19

M(g) → M+(g) + e−

Question 20

What are the three main factors affecting ionisation energy?

Answer 20

1) The attraction of the nucleus (more protons in the nucleus means greater attraction)
2) The distance of the electrons from the nucleus (the bigger the atom, the further the outer electrons are from the nucleus and the weaker the attractive force)
3) Shielding of the Attraction from the Nucleus (a greater number of electrons in inner shells will repel those in the outer shell, weakening the attraction of the nucleus).

Question 21

How can we identify what group an unknown element is in using its successive ionisation energies?

Answer 21

We can look for a big jump, which shows us that the next electron is removed from an inner shell. This indicates how many electrons were in the outer shell.

Question 22

Why has Helium got the largest first ionisation energy?

Answer 22

Its first electron is in the first shell closest to the nucleus and has no shielding effects from inner shells. He has a bigger first ionisation energy than H as it has one more proton.

Question 23

Why do first ionisation energies decrease down a group?

Answer 23

As one goes down a group, the outer electrons are found in shells further from the nucleus and are more shielded so the attraction of the nucleus becomes smaller.

Question 24

Why is there a general increase in first ionisation energy across a period?

Answer 24

As one goes across a period the electrons are being added to the same shell which has the same distance from the nucleus and same shielding effect. The number of protons increases, however, making the effective attraction of the nucleus greater.

Question 25

Why is there a small drop from Mg to Al in 1st ionisation energy?

Answer 25

Al is starting to fill a 3p sub shell, whereas Mg has its outer electrons in the 3s sub shell. The electrons in the 3p subshell are slightly easier to remove because the 3p electrons are higher in energy and are also slightly shielded by the 3s electrons.

Question 26

Why is there a small drop from P to S in ionisation energy?

Answer 26

With sulphur there are 4 electrons in the 3p sub shell and the 4th is starting to doubly fill the first 3p orbital. When the second electron is added to a 3p orbital there is a slight repulsion between the two negatively charged electrons which makes the second electron easier to remove.

Question 27

What element has the highest second ionisation energy?

Answer 27

Lithium - its first electron would be removed from the 2s shell. its second electron is removed from the 1st shell, closest to the nucleus, which has no shielding effects from inner shells. It has a bigger second ionisation energy than He due to a higher nuclear charge.

Question 28

What was the gold foil atomic experiment?

Answer 28

Alpha particles were fired at a thin sheet of gold foil. Most passed straight through. Only a few were deflected straight backwards. This disproved the plum pudding model, which would have expected most to be slightly deflected.

Question 29

What atomic model was developed after the gold foil experiment?

Answer 29

The nuclear model of the atom: A tiny positively charged nucleus surrounded by a cloud of negative electrons. Most of the atom was empty space.

Question 30

Explain the 1803 John Dalton model.

Answer 30

Atoms are sphered.

Question 31

Explain the pattern in the first ionisation energies of the elements from lithium to neon.

Answer 31

The first ionisation energies increase across the period as nuclear charge increases.

Question 32

Do chemical properties of isotopes differ?

Answer 32

No, they all have the same chemical properties as electron configuration remains the same.

Question 33

Describe how Ions are formed and detected at a Time of Flight Mass spectrometer.

Answer 33

1) Ion Formation: Apply a high voltage to a sample in a polar solvent; where the sample gains a proton.
2) Detected: Ions hit a plate causing the movement of electrons; generating a current.

Question 34

Explain Acceleration in TOF Mass Spectrometry.

Answer 34

Electric field is applied to give all the ions with the same charge a constant kinetic energy; lighter particles move faster.

Question 35

Purpose of the mass spectrometer.

Answer 35

To analyze the mass-to-charge ratio of ions.

Question 36

Why does TOF need to be under a vacuum?

Answer 36

To prevent air particles ionising and registering on the detector.

Question 37

Explain Electron Impact Ionisation.

Answer 37

A sample is vaporised and bombarded with high-energy electrons, resulting in the removal of an electron from each particle, creating positive ions.

Question 38

When is Electron impact ionisation used?

Answer 38

For small molecules and volatile compounds.

Question 39

What is Electrospray Ionisation?

Answer 39

A method used to produce ions from large biomolecules by dissolving them in a polar solvent and applying a high voltage.

Question 40

Formula to calculate velocity.

Answer 40

v = d/t

Question 41

Why are Successive Ionisation Energies always larger?

Answer 41

Because each successive electron is removed from a positively charged ion, which requires more energy.

Question 42

Define Relative atomic mass.

Answer 42

The weighted average mass of the isotopes of an element, taking into account their abundances, measured relative to one-twelfth of the mass of an atom of carbon-12.

Question 43

Why are there peaks with lower m/z ratios?

Answer 43

Due to fragmentation.

Question 44

Explain why the second ionisation energy is greater than the first ionisation energy.

Answer 44

An electron is being removed from a positive ion (therefore needs more energy) and the electron being removed is closer to the nucleus.

Question 45

What is an isotope?

Answer 45

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons, resulting in different atomic masses.

Question 46

Describe the structure of an atom.

Answer 46

An atom consists of a nucleus containing protons and neutrons, surrounded by electrons that orbit the nucleus in electron shells.

Question 47

How is the atomic number defined and what does it signify?

Answer 47

The atomic number is the number of protons in an atom’s nucleus and defines the element to which the atom belongs.

Question 48

Explain the concept of mass number.

Answer 48

The mass number is the total number of protons and neutrons in an atom’s nucleus.

Question 49

What is the relative atomic mass (Ar) and how is it calculated?

Answer 49

The relative atomic mass (Ar) is the weighted average mass of the isotopes of an element, taking into account their abundances, measured relative to one-twelfth of the mass of an atom of carbon-12.

Question 50

Define ionisation energy and discuss its periodic trend.

Answer 50

Ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions. Ionisation energy generally increases across a period due to increasing nuclear charge and decreases down a group due to increasing electron shielding.

Question 51

What is electron configuration and how does it relate to the periodic table?

Answer 51

Electron configuration is the arrangement of electrons in an atom’s shells and subshells. The periodic table is structured in such a way that elements with similar electron configurations are grouped together, showing similar chemical properties.

Question 52

Explain what is meant by the term ‘orbital’ and name the different types.

Answer 52

An orbital is a region around the nucleus of an atom where there is a high probability of finding an electron. The main types of orbitals are s, p, d, and f.

Question 53

Define ‘relative atomic mass’ (Ar).

Answer 53

Relative atomic mass (Ar) is the weighted average mass of the isotopes of an element, scaled relative to carbon-12.

Question 54

What is meant by the term ‘orbital’?

Answer 54

An orbital is a region around the nucleus of an atom where there is a high probability of finding an electron.

The main types of orbitals are s, p, d, and f.

Question 55

Define ‘relative atomic mass’ (Ar).

Answer 55

Relative atomic mass (Ar) is the weighted average mass of the isotopes of an element, scaled relative to carbon-12, which is assigned a mass of exactly 12 atomic mass units.

Question 56

Explain what an electron shell is.

Answer 56

Electron shells are the paths in which electrons orbit the nucleus of an atom, with each shell corresponding to a particular energy level.

Question 57

Describe the trend in ionisation energy across a period.

Answer 57

Across a period, ionisation energy generally increases due to the increase in nuclear charge which attracts the electrons more strongly, reducing atomic radius.

Question 58

Describe the trend in ionisation energy down a group.

Answer 58

Down a group, ionisation energy generally decreases as atomic radius increases, electron shielding effect increases, and less energy is required to remove an electron.

Question 59

What is electron configuration?

Answer 59

Electron configuration is the arrangement of electrons in an atom’s orbitals, shells, and subshells according to the principles of quantum mechanics.

Question 60

How many electrons can the s, p, d, and f orbitals hold, respectively?

Answer 60

The s orbital can hold 2 electrons, p orbital can hold 6, d orbital can hold 10, and f orbital can hold 14 electrons.

Question 61

How do isotopes of an element differ in their physical properties?

Answer 61

Isotopes of an element differ in physical properties such as melting point, boiling point, and mass, due to differences in the number of neutrons, which affect the atomic mass but not chemical properties.

Question 62

What is the relative mass and charge of a proton?

Answer 62

A proton has a relative mass of 1 and a relative charge of +1.

Question 63

What is the relative mass and charge of a neutron?

Answer 63

A neutron has a relative mass of 1 and no charge (neutral).

Question 64

What is the relative mass and charge of an electron?

Answer 64

An electron has a relative mass of 1/1840 and a relative charge of -1.

Question 65

What do isotopes of an element typically have in common?

Answer 65

Isotopes have similar chemical properties due to having the same electronic structure.

Question 66

Describe the principle of a mass spectrometer.

Answer 66

A mass spectrometer is used to determine all the isotopes present in a sample of an element by measuring the mass-to-charge ratio (m/z) and abundance of ionized atoms or molecules.

Question 67

State the four main steps involved in mass spectrometry.

Answer 67

The four main steps are ionisation, acceleration, flight tube (time of flight measurement), and detection.

Question 68

Explain the ionisation step in mass spectrometry.

Answer 68

In ionisation, a sample is ionized by techniques like electron impact or electrospray, where electrons are knocked out or added, forming ions.

Question 69

What happens during the acceleration step in mass spectrometry?

Answer 69

During acceleration, positive ions are accelerated by an electric field to a constant kinetic energy.

Question 70

Describe the flight tube in a mass spectrometer.

Answer 70

In the flight tube, ions are separated based on their mass-to-charge ratios; lighter ions travel faster and reach the detector sooner than heavier ions.

Question 71

What occurs at the detection stage of mass spectrometry?

Answer 71

Ions reach the detector, which measures the size of an ion current that is proportional to the abundance of the species.

Question 72

How does electron impact ionisation work?

Answer 72

A vaporized sample is bombarded with high-energy electrons from an electron gun, knocking out outer electrons and forming positive ions.

Question 73

Describe electrospray ionisation.

Answer 73

In electrospray ionisation, the sample in a volatile solvent is sprayed through a high-voltage needle, forming solvent-coated ions that lose the solvent as they move towards a detector.

Question 74

Explain how the relative atomic mass (R.A.M) is determined using a mass spectrometer.

Answer 74

R.A.M is calculated as the sum of the products of isotopic masses and their relative abundances, divided by 100.

Question 75

Calculate the R.A.M (Relative atomic mass) of magnesium if its isotopes have masses of 24, 25, 26 and relative abundances of 78.70%, 10.13%, 11.17% respectively.

Answer 75

R.A.M = [(78.7 x 24) + (10.13 x 25) + (11.17 x 26)] / 100 = 24.3.

Question 76

How do the models of atomic structure differ in their explanation of electron behavior?

Answer 76

Early models like Bohr’s suggested electrons travel in fixed orbits, while modern quantum mechanical models describe electrons in terms of probabilities within orbitals.

Question 77

Define the first ionisation energy.

Answer 77

First ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions with a single positive charge.

Question 78

What factors affect ionisation energy?

Answer 78

Ionisation energy is affected by nuclear attraction, distance of the electrons from the nucleus, and electron shielding by inner shells.

Question 79

Why does ionisation energy generally increase across a period?

Answer 79

Ionisation energy increases across a period due to an increase in nuclear charge, which attracts electrons more strongly, overcoming any increase in shielding.

Question 80

Why is there a general decrease in ionisation energy down a group?

Answer 80

Ionisation energy decreases down a group as atomic size increases, leading to greater electron shielding and weaker nuclear attraction at greater distances.

Question 81

What is meant by the ‘second ionisation energy’?

Answer 81

The second ionisation energy is the energy required to remove a second electron from one mole of gaseous ions with a single positive charge to form one mole of gaseous ions with a double positive charge.

Question 82

Describe why successive ionisation energies of an element are always larger.

Answer 82

Each successive ionisation energy is larger because the remaining electrons experience a stronger effective nuclear charge due to reduced electron shielding after each electron is removed.

Question 83

How can ionisation energies provide insights into electronic structure?

Answer 83

Patterns in successive ionisation energies can indicate the electron configuration of an element, such as identifying the point at which electrons start being removed from an inner, more tightly bound shell.

Question 84

Why do first ionisation energies decrease down a group in the periodic table?

Answer 84

First ionisation energies decrease down a group as the outer electrons are increasingly farther from the nucleus and more shielded by inner electrons, reducing the nuclear attraction.

Question 85

How does the electronic structure affect the chemical properties of an element?

Answer 85

The electronic structure determines how an element interacts with others, influencing its reactivity, the types of bonds it can form, and its placement in the periodic table.

Question 86

Why does helium have a higher first ionisation energy than hydrogen?

Answer 86

Helium has a higher first ionisation energy because it has more protons in its nucleus, resulting in a stronger attraction to the electrons compared to hydrogen.

Question 87

Why is there a drop in first ionisation energy from magnesium to aluminum?

Answer 87

The drop in first ionisation energy from magnesium to aluminum occurs because aluminum starts to fill a 3p orbital, which is higher in energy and slightly more shielded by 3s electrons.

Question 88

What causes the slight drop in first ionisation energy from phosphorus to sulfur?

Answer 88

The drop from phosphorus to sulfur is due to the pairing of electrons in the 3p orbital in sulfur, causing slight electron-electron repulsion, which makes it easier to remove an electron.

Question 89

What pattern is observed in the second ionisation energies across a period?

Answer 89

Second ionisation energies generally show a similar pattern to first ionisation energies but shifted left, indicating removal of electrons from an increasingly positive ion.

Question 90

Explain why lithium has a high second ionisation energy.

Answer 90

Lithium’s second ionisation energy is high because the second electron is removed from the 1s orbital, which is very close to the nucleus and has no shielding effect.

Question 91

How does electron impact ionisation potentially affect molecular samples?

Answer 91

Electron impact ionisation can cause larger organic molecules to fragment, altering the mass spectrum by producing peaks for fragments besides the molecular ion.

Question 92

Describe a scenario where electrospray ionisation is preferred over electron impact.

Answer 92

Electrospray ionisation is preferred for larger organic molecules because it operates under softer conditions that prevent fragmentation, preserving the whole molecule in the spectrum.

Question 93

Explain the difference in detection between molecular ions in electron impact and electrospray ionisation.

Answer 93

In electron impact, the molecular ion peak is the base peak for the intact molecule, while in electrospray ionisation, the MH+ peak appears and needs a mass adjustment by subtracting one to find the molecular mass.

Question 94

What unique feature is observed in the electronic structure of chromium and copper?

Answer 94

Both chromium and copper exhibit unusual electronic configurations: chromium has a 4s1 3d5 arrangement, and copper has a 4s1 3d10, to achieve more stable and symmetrical electron arrangements.

Question 95

Explain the significance of the shape and orientation of p orbitals.

Answer 95

The shape and orientation of p orbitals (dumbbell-shaped) allow for the overlap in covalent bonds, particularly pi (π) bonding, which is essential for the formation of double bonds between atoms.

Question 96

How do s and p sublevels differ in shape?

Answer 96

S sublevels are spherical, encompassing the nucleus symmetrically, while p sublevels are dumbbell-shaped.

Question 97

Why is it important to fill orbitals singly before pairing electrons?

Answer 97

Electrons fill orbitals singly before pairing to minimise electron-electron repulsion within an orbital.