Chapter 1- Atomic structure

Question 1

What is the atomic number (Z) ?

Answer 1

The number of protons in the nucleus of an atom

Question 2

What is the mass number (A) ?

Answer 2

The SUM of the number of protons and neutrons in a nucleus (total number of nucleons)

Question 3

Charges of sub-atomic particles

Answer 3

Proton: 1+
Neutron: 0
Electron: 1-

Question 4

Mass of sub-atomic particles

Answer 4

Proton: 1
Neutron: 1
Electron: 1/2000 (negligible)

Question 5

What are isotopes?

Answer 5

Atoms of the same element with the same number of protons (atomic number) but different number of neutrons (mass number).
They have similar chemical properties.

Question 6

What is an ion?

Answer 6

A charged particle by the gain or loss of electrons

Question 7

What are two uses of Time of Flight (TOF) mass spectrometry?

Answer 7

-Identifying elements or molecules within samples
-Determining relative atomic or molecular mass

Question 8

What are the stages of TOF mass spectrometry?

Answer 8

-Ionisation, acceleration, ion drift, ion detection, data analysis

Question 9

What are the two types of ionisation used in TOF mass spectrometry?

Answer 9

-Electron impact and electrospray ionisation

Question 10

What is the process of electron impact ionisation?

Answer 10

-Sample is vaporised and gaseous particles are bombarded with beam of energetic electrons.
-Electron gun (hot wire filament with current flowing through it emitting electrons) knocks off one electron from each particle forming 1+ ions.
-Causes fragmentation.

Question 11

What is the process of electrospray ionisation?

Answer 11

-Sample is dissolved in volatile solvent (eg water or methanol) and injected through fine hypodermic needle creating an aerosol (fine mist).
-Tip of needle connected to high voltage power supply and particles gain a proton from the solvent while leaving the needle.
-Solvent evaporates and XH+ ions are accelerated.

Question 12

What is the equation for electron impact ionisation?

Answer 12

X (g) + e- —> X+ (g) + 2e-
or
X (g) —> X+ (g) + e-

Question 13

What is the equation for electrospray ionisation?

Answer 13

X (g) + H+ —> XH+ (g)

Question 14

What happens during acceleration?

Answer 14

-Positive ions are attracted to negative plates, causing them to accelerate towards the flight tube and giving them all the same kinetic energy.

Question 15

What happens during ion drift?

Answer 15

-A beam of positive ions is produced . The ions leave the electric field and drifts down the flight tube separating depending on their mass.
-When all ions have the same charge, lighter ions have a higher speed as they all have the same kinetic energy.

Question 16

What happens during ion detection?

Answer 16

-At the end of the flight tube is a negatively charged detector plate. When the ions reach the end of the tube, they hit the plate and gain electrons, discharging them.
-This causes a current to flow which is proportional to the abundance of ions hitting the plate.

Question 17

How is data collected and analysed?

Answer 17

-When the ions are discharged at the detector, a current flows that is proportional to the abundance of ions hitting the plate.
-The mass spectrometer uses the data to produce a mass spectrum.
-It shows relative abundance (y axis) against mass/charge ratio (x axis). As most are 1+ ions, the m/z ration practically shows the ions’ masses.

Question 18

What are three names for shells?

Answer 18

Shell
Quantum shell
Energy level

Question 19

What are three names for sub-shells?

Answer 19

Sub-shell
Orbital
Sub-energy level

Question 20

What is the order of the orbitals?

Answer 20

s, p, d, f

Question 21

How many electrons can an s orbital hold?

Answer 21

2 electrons (spherical)

Question 22

How many electrons can a p orbital hold?

Answer 22

6 electrons, 3 pairs of 2 (dumbell)

Question 23

How many electrons can a d orbital hold?

Answer 23

10 electrons, 5 pairs of 2

Question 24

How many electrons can an f orbital hold?

Answer 24

14 electrons

Question 25

What happens to shells as the distance from the nucleus increases?

Answer 25

-Energy levels get closer together (converge) causing orbitals to overlap, eg 4s fills before 3d, 4p before 5s, etc.

Question 26

What are the two stable electron configurations in orbitals?

Answer 26

-Maximum unpairing and maximum pairing
-Maximum unpairing: one electron per dumbbell as electrons repel each other
-Maximum pairing: two electrons in each dumbbell (paired up)

Question 27

Which block is group 1 and 2 in?

Answer 27

s block (outer electrons in s orbitals)

Question 28

Which block are the transition elements in?

Answer 28

d block (outer electrons in d orbitals)

Question 29

Which block are groups 3 to 8 in?

Answer 29

p block (outer electrons in p orbitals)

Question 30

What are the two anomalous electron configurations?

Answer 30

Copper and chromium

Question 31

What is copper’s electron configuration?

Answer 31

1s2 2s2 2p6 3s2 3p6 4s1 3d10
-Maximum pairing in 3d10 is more stable than 3d9 so 4s1 is not filled completely

Question 32

What is chromium’s electron configuration?

Answer 32

1s2 2s2 2p6 3s2 3p6 4s1 3d5
-Maximum unpairing in 3d5 is more stable than 3d4 so 4s1 is not filled completely

Question 33

How do pairs of electrons in the same orbital spin?

Answer 33

-Have opposite spin as they repel each other as they have like negative charges

Question 34

What is the first ionisation energy?

Answer 34

The amount of energy required to remove one mole of electrons from one mole of gaseous atoms to produce one mole of gaseous mono-positive (1+) ions

Question 35

Why is second ionisation energy (and so on) greater than first ionisation energy?

Answer 35

When removing the second electron, the atom is now a positive ion, meaning more energy is required to overcome the electrostatic force of attraction between the positive ion and electron.

Question 36

How does first ionisation energy change across a period?

Answer 36

-First ionisation energy increases
-The number of shells, and so amount of shielding, stays the same across the period. Nuclear charge (no. of protons) increases meaning greater attractive force has to be overcome by more energy.

Question 37

How does first ionisation energy change down a group?

Answer 37

-First ionisation energy decreases
-Although nuclear charge increases, the number of shells also increases going down the group so greater distance from nucleus and amount of shielding so less energy required to remove outermost electron.
-Decreases by less each time due to convergence of shells.

Question 38

What is relative atomic mass?

Answer 38

-The average mass of one atom on a scale where 1/12 the mass of a carbon-12 atom is 1

Question 39

What is the equation for first ionisation energy?

Answer 39

X (g) –> X+ (g) + e-

Question 40

What is the equation for second ionisation energy?

Answer 40

X+ (g) –> X2+ (g) + e-

Question 41

Why does the 3rd element in a period (eg B) have a lower first ionisation energy than the 2nd element (eg Be)?

Answer 41

In the 2nd element, the outermost electron is in the 2s2 or 3s2 orbital.
In the 3rd element, it is in the 2p1 or 3p1 orbital which is of a higher energy (further from nucleus) so requires less energy to be removed.

Question 42

Why does the 6th element in a period (eg O) have a lower first ionisation energy than the 5th element (eg N)?

Answer 42

In the 5th element, the electrons in 2p3 or 3p3 orbital are in maximum unpairing.
In the 6th element, they aren’t as 2 electrons have to pair up in a dumbbell; these repel each other, meaning it takes less energy to remove one.