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Chemistry A Level > Atomic Structure > Flashcards

Atomic Structure Flashcards

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1
Q

What is the purpose of a time of flight mass spectrometer ?

A

It gives accurate information about relative isotopic mass and the relative abundance of isotopes. It can also be used to determine relative molecular mass and to identify elements

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2
Q

What is relative isotopic abundance ?

A

The relative amount of each isotopic present in a sample of an element

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3
Q

What is relative isotopic mass ?

A

The mass of an atom on an isotope of an element compared with 1/12 the mass of C-12

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4
Q

What is relative atomic mass ?

A

The weighted mean mass of an atom of an element compared with 1/12 the mass of C-12

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5
Q

What is the relative molecular mass ?

A

The mean weighted mass of a molecule compared to 1/12 the mass of C-12

molecular - covalent molecules
formula - formula unit (e.g NaCl)

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6
Q

What are the simple stages of TOF mass spectroscopy ?

A
  1. Squirt sample into TOF mass spectrometer
  2. Ionise sample (through electron impact ionisation or electrospray ionisation)
  3. Accelerate ions using electric field
  4. Ion drift (through tube with no electric field)
  5. Detection through hitting negatively charged plate
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7
Q

Describe electron impact ionisation ?

A
  1. Sample vaporised
  2. High energy electrons fired at vapour from an “electron gun”
  3. Electrons knocked off from element forming +1 ions (molecular ion)
  4. Ions attracted to negative electric plate

e.g. CH4 (g) –> CH4+ (g) + e-

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8
Q

What is an “electron gun” ?

A

A hot wire filament with current flowing through it, emitting electrons

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9
Q

What causes fluctuations using electron impact ionisation ?

A

Some particles may break into small fragments which are detected (fragmentation)

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10
Q

When do we use electron impact ionisation ?

A

For elements AND substances with a low formula mass

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11
Q

Describe electrospray ionisation ?

A
  1. Sample dissolved in volatile substance (e.g. water/methanol) and injected through fine hypodermic needle to give fine mist
  2. Needle tip attached to positive terminal of power supply causing particles to gain a proton (H+)
  3. Solvent evaporated whilst XH+ ions attracted to negative electric plate

X(g) + H+ –> XH+ (g)

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12
Q

When do we use electrospray ionisation ?

A

For substances with a higher molecular mass such as biological molecules (e.g. proteins)

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13
Q

Why is the acceleration stage important ?

A

It accelerates ions using an electric field so that they all have the same kinetic energy. This means that each ion’s velocity is dependant on m/z with lighter particles having a greater velocity (inverse proportion)

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14
Q

What is ion drift ?

A

Pass through flight tube, with the time each molecule takes depending on its velocity, which in turn depends on its mass. This means lighter particles reach the detector in less time

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15
Q

How is the detection phase used to produce a mass spectrum on a computer ?

A

Positive ions hit negatively charged plate and are discharged (form neutral atoms) by gaining electrons. This generates electron movement, so an electric current can be measured. The size of current measure equals the number of ions hitting the plate

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16
Q

What does the m/z represent ?

A

mass/ charge where charge is +1, so it gives us the ion mass

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17
Q

How can we find the relative molecular mass using a mass spectrum ?

A

The highest m/z peak value because this comes from the molecular ion.

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18
Q

What is the differences between the mass spectrum for electron impact ionisation and electrospray ionisation ?

A
  1. Electron impact has peaks before the molecular mass because of fragmentation, whereas electrospray doesn’t as it is a soft process.
  2. The molecular mass using electron impact is the furthest peak on the graph, but using electrospray it is the furthest peak - 1 (to remove the mass of the proton during collision)
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19
Q

How can we work out the relative atomic mass from the mass spectrum ?

A

Combined mass of all isotopes / combined abundance of all isotopes

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20
Q

What is the relative mass and charge of a proton ?

A

charge = 1+
mass = 1

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21
Q

What is the relative mass and charge of a neutron ?

A

charge = 0
mass = 1

22
Q

What is the relative mass and charge of an electron ?

A

charge = 1-
mass =1/1850

23
Q

What is the structure of the atom ?

A

It consists of a nucleus containing protons and neutrons surrounded by electrons

24
Q

Briefly describe the A-level electronic configuration model ?

A

Electrons move quickly from from one place to another within regions of empty space, as to create a cloud.

We cannot assume the exact and defined position of an electron, but can use probability and a 3D map for the likelihood of where an electron is.

25
Q

Describe the electronic configuration heirachy ?

A

Energy levels are made up of different sub-levels.

Sub-levels are made up of different orbitals (region of shape where finding an electron is maximum)

Each orbital can be occupied by a maximum of two electrons

26
Q

What are the different types of sub-levels ?

A

S sub-level (one orbital)
P sub-level (three orbitals)
D sub-level (five orbitals)
F-orbital (not needed for spec)

27
Q

How do we write electronic configuration ?

A
  1. Write the number of the energy level (1,2,3 etc.)
  2. Write the sub-level being occupied (S, P, D)
  3. Write the number of electrons that the sub-level holds (1-10) as a small number
28
Q

What model can we use to display electronic configuration and when is it used?

A

We can use the ‘electrons in boxes’ (where each box represents an orbital) method as drawing electronic configuration can easily become too difficult

29
Q

Why are electron arrows drawn to point in opposite directions when using the ‘electrons in boxes ‘method ?

A

It shows the electrons spinning in opposite directions to reduce the repulsion experienced

30
Q

How do we fill sub-levels with more than one orbital ?

A

Electrons will occupy separate orbitals before they have to share an orbital to increase stability

31
Q

How can we write out simplified electronic configuration ?

A

We write the name of the noble gas element before the element we are writing in square brackets, and then write out the additional sub-levels after

32
Q

Why do different elements belong to different blocks ?

A

Which sub-level the elements outermost electrons are found in determine their block

33
Q

Why are electrons added to the 4s outershell before the 3d outershell ?

A

When the 4s sub-level is empty, it has less energy than the 3d sub-level meaning it is filled first so that the outershell electrons have the highest energy

34
Q

Which shell do we remove electrons first when the atomic number is greater than 21 (transition metals)

A

4s because when filled, the 4s sub-level has a energy than the 3d sub-level

35
Q

Write out the electronic configuration of chromium (Z=24)

A

[Ar]4s1, 3d5

This is because an electron jumps from the 4s orbital to the 3d orbital where there is an empty orbital, reducing repulsion)

Copper is also a part of this rule

36
Q

How do we calculate the mass of an ion in time of flight calculations ?

A

(0.001 g / 6.022 x10^23) x RAM of the element

37
Q

What three formulas do you need for time of flight calculations ?

A

Ke = 1/2mv^2
D = v x t
t = d x srt(m/2E)

38
Q

Define first ionisation energy ?

A

The first ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms of an element to form one mole of 1+ ions

39
Q

What factors affect ionisation energy ?

A
  1. Nuclear charge
  2. Shielding due to inner electrons
  3. Distance between the outermost electron removed and the nucleus
40
Q

Give the formula for the first ionisation energy of an element X ? Include state symbols.

A

X (g) –> X+(g) + e-

41
Q

Give the formula for the fourth ionisation energy of an element X ? Include state symbols.

A

X3+ (g) –> X4+ (g) + e-

42
Q

What is the general trend in ionisation energies across period three ? Explain this trend.

A

As you go across period three, ionisation energy of each element gradually increases. This is because as you go across the period, nuclear charge increases which causes a greater force of electrostatic attraction between the outermost electron and the nucleus. As electrons are added to the same energy level, this means that they all experience similar shielding.

43
Q

What are the anomalies to the trend across period three ?

A

Mg - Al ionisation energy drop
P-S ionisation energy drop

44
Q

Explain the Mg-Al drop in ionisation energy in period three ?

A

In Mg, the electron being removed is from the 3s sub-level, whereas in Al, the electron is removed from the 3p sub-level. This means that in Al, the electron is further away from the nucleus and therefore experiences a weaker force of electrostatic attraction (higher energy level). The electron being removed in Al also experiences a greater force of shielding from inner electrons. This means that the electron is therefore less tightly held by the nucleus compared to the electron being removed from Mg, so therefore requires less energy to be removed.

45
Q

Explain the P-S drop in ionisation energy in period three ?

A

In P, the 3p sub-level is occupied by three electrons. This means each orbital is single-filled. However, in S, the 3p sub-level is occupied by four electrons. This means that one orbital is double-filled. This means that the electrons sharing an orbital experience a force of repulsion, so it is easier to remove an electron from the orbital. This therefore means a lower ionisation energy compared to the single-filled orbital in P

46
Q

In period three, which element has the highest second ionisation energy ?

A

Na because the second electron is removed from the 2p sub-level. This means that the electron being removed is closest to the nucleus, so therefore experiences the strongest force of electrostatic attraction between the nucleus and outermost electron (lower energy level). It also experiences the least shielding from inner electrons. Therefore, it is the most tightly held by the nucleus and requires the most energy to be removed

47
Q

In period three, which element has the highest second ionisation energy ?

A

Na because the second electron is removed from the 2p sub-level. This means that the electron being removed is closest to the nucleus, so therefore experiences the strongest force of electrostatic attraction between the nucleus and outermost electron (lower energy level). It also experiences the least shielding from inner electrons. Therefore, it is the most tightly held by the nucleus and requires the most energy to be removed

48
Q

Describe the trend in ionisation energy as you go down group two ? Explain this trend.

A

As you go down group two, ionisation energy decreases. This is because as you go down the group, atom size increases as more energy levels are occupied by electrons. Therefore, the outermost electron being removed is a greater distance from the nucleus, so experiences a weaker force of electrostatic attraction between the nucleus. As you go down, the effect of shielding due to inner electrons also increases. This causes the electron to be less tightly held by the nucleus and easier to remove as you go down the group

49
Q

How can we determine which group an element is in based on successive ionisation energies ?

A

The first big jump in ionisation energy indicates the group number. This is because it suggests the ionisation energy that increases greatly is in a lower energy level than the previous electron, so it is closer to the nucleus and experiences a greater force of electrostatic attraction. It also therefore experiences less shielding from inner electrons. This means the electron is more tightly held by the nucleus and requires more energy to be removed. Therefore, the ionisation energy before the jump indicates the number of outermost electrons, and group number.

50
Q

Why will an ion of magnesium have a higher ionisation energy than an atom of neon, despite having the same number of electrons ?

A

Although both experience the same effect of shielding from inner electrons, and both have electrons removed from the same orbital, magnesium has a higher nuclear charge. This means that the electron being removed experiences a greater force of electrostatic attraction between the nucleus, is more tightly held by the nucleus and requires more energy to be removed.

Chemistry A Level (3 decks)

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