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A-level AQA Chemistry > Physical: Atomic Structure > Flashcards

Physical: Atomic Structure Flashcards

1
Q

What is the relative mass of an electron?

A

1/1840

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2
Q

Why are there no units for relative mass/charge?

A

It’s because the values are relative to one another, it’s a COMPARISON and the actual values are too small

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3
Q

How should you draw electrons in diagrams?

A

by using crosses

X

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4
Q

How are electrons arranged?

A

in energy LEVELS (not shells)

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5
Q

What is the atomic number and its symbol?

A

the number of protons in the nucleus.
number of protons defines the element
Z

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6
Q

What is mass number and its symbol?

A

TOTAL number of protons and neutrons in the nucleus

A

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7
Q

What is an ion?

A

a charged particle formed when an atom gains or loses and electron

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8
Q

What is an isotope?

A

atoms of the same element that have the same number of protons and have a different number of neutrons

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9
Q

What are the three main physical properties?

A

boiling point
melting point
density

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10
Q

Do isotopes have similar chemical properties?

A

yes, because isotopes have the same number of electrons in outer shell
AND have the same electron configuration

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11
Q

Do isotopes have similar physical properties?

A

No, they have different physical properties because isotopes have different mass numbers (due to diff. number of neutrons).

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12
Q

What is the difference between relative atomic mass and mass number?

A

rel. atomic mass= MEAN mass of an atom on a scale where an atom of C-12 is exactly 12 (taking isotopes into account) *** can be a decimal number
mass number= number of protons and neutrons ** has to be a full number

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13
Q

What instrument can be used to find the relative proportions of an element?

A

mass spectrometer

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14
Q

What are the 4 stages (+1 extra) of mass spectrometry?

A
  1. ionisation (by either electron impact or electrospray ionisation)
  2. acceleration
  3. ion drift
  4. detection
  5. data analysis
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15
Q

What is the process of electron impact?

A

method of ionising elements

  • sample is vaporised
  • high energy particles are fired from an ELECTRON GUN
  • they bombard a sample
  • knock one OUTER electron off forming a 1+ ion
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16
Q

What type of ions can electron impact work with?

A

usually, low Mᵣ ions

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17
Q

What is the formula for electron impact?

A

X₍g₎——> X⁺₍g₎ + e⁻

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18
Q

What is the con of electron impact?

A

it can cause fragmentation (breaking the ion)

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19
Q

What is the process of electrospray ionisation?

A
  • sample is dissolved in a volatile solution
  • it is injected through a fine hypodermic needle, producing a fine mist
  • tip of the needle has a high voltage
  • each particle gains a H⁺ (proton) to form a 1+ ion
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20
Q

What type of ions does electrospray ionisation work with?

A

high Mᵣ ions

this is because they are more likely to fragment so cannot use electron impact method

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21
Q

What is the formula for electrospray ionisation?

A

X₍g₎ + H⁺ ——–> XH⁺ ₍g₎

always include state symbols

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22
Q

What is the process of acceleration (mass spectrometry)?

A
  • the +ions are accelerated in an ELECTRIC FIELD by a force of attraction by a negatively charged plate
  • until they all have CONSTANT kinetic energy (not speed)
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23
Q

Does mass affect velocity of ions in mass spectrometry?

A

yes,

  • heavier ions are slower
  • lighter ions are faster
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24
Q

What is ion drift?

A
  • ions enter a FLIGHT TUBE directed towards a director

- length of time to reach the detector depends on the mass/velocity

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25
Q

Does a heavier ion a shorter/longer flight time?

A

a heavier ion has a longer flight time

a lighter ion has a shorter flight time

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26
Q

What is the formula for time of flight along flight tube?

A

t= d* √m/2KE

substitute distance/time into velocity of kinetic energy formula

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27
Q

What is detection (mass spectrometry)?

A
  • the + ions hit a negatively charged plate
    • ions gain electrons
  • movement of e⁻ generates an electric current
  • size of current is proportional to the number of ions gaining e⁻
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28
Q

What is the name of the graph produced from mass spectrometry?

A

mass spectra

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29
Q

What does the number of peaks on a mass spectra indicate?

A

the number of peaks = number of isotopes

most abundant one has the highest peak

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30
Q

What is the definition of ionisation energy?

A

the energy change when one mole of electrons are removed from one mole of GASEOUS atoms to form 1 mole of gaseous positively charged ions

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31
Q

What is the formula for first ionisation ?

A

X(g) ————> X⁺₍₉₎ + e⁻

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32
Q

Can non-metals be ionised?

A

all elements can be ionised, even the ones that normally form 1- ions (non-metals)

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33
Q

What state must the elements be in to become ionised?

A

always must be in a GASEOUS state

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34
Q

What are the factors affecting ionisation energy?

A
  • shielding
  • nuclear strength
  • distance from the nucleus
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35
Q

How does nuclear charge/strength affect ionisation energy?

A
  • more protons there are in the nucleus, stronger the nuclear attraction for valence e⁻
  • more energy needed to remove the e⁻, greater I.E
36
Q

How does distance form the nucleus affect ionisation energy?

A
  • further from the nucleus the valence electron is, the weaker the nuclear attraction
  • less energy required to remove e⁻
  • lower I.E
37
Q

How does shielding affect ionisation energy?

A
  • greater the number of inner e⁻ between the nucleus and the valence e⁻
  • weaker the nuclear attraction (between nucleus and valence e⁻)
  • less energy required to remove valence e⁻
  • lower I.E
38
Q

What ion would have the greatest ion drift?

A

the lightest ion

39
Q

What is the trend for the first ionisation energies down Group 2?

A

as you go down the group, the IE₁ decreases

  • each element has one more electron shell than the one above it
  • the extra shell, means more shielding e⁻ and an increasing distance from the nucleus which reduces the nuclear attraction
  • so less energy required to remove the outer e⁻
40
Q

What are the ionisation trends across Period 3?

A

across a period, IE tend to increase because:

  • this is because the number of protons increase as you go across a period (so nuclear strength increases)
  • however, all extra electrons are at the same shells so not much change in shielding and distance
  • so more energy required to remove the outer e⁻
41
Q

What is the shape of the graph for ionisation energies across Period 3?

A 
up
down
up
up
down
up
up
42
Q

What is the trend for successive ionisation energies of elements?

A

-general increase

43
Q

Explain why there is a huge jump on graphs for successive ionisation energies of elements

A

there are big jumps when a new energy shell is broken into, so outer e⁻ are closer to nucleus and fewer shielding e⁻ os nuclear attraction increases, more energy required to remove outer e⁻

44
Q

Explain why there is a gradual increase on graphs for successive ionisation energies of elements?

A

within each shell, successive ionisation energies increase gradually because e⁻ are being removed from an increasingly positive ion, so there is less repulsion amongst the remaining e⁻, so they’re held more strongly by the nucleus, so less of a big jump

45
Q

During mass spectrometry, why could the relative atomic mass be different from its actual value?

A

this could be due to other isotopes present

46
Q

Why could there be a small peak on a mass spectra that is half the actual relative atomic mass?

A

it could be because a two + ion is formed from the isotope that it is half of
e.g- if a peak is at 64 for Te 128 (not Te 126 which is another isotope)

47
Q

Would the atomic radius of ¹²⁴Te be larger than ¹³⁰Te?

A

it would be the same because they both have the same number of electrons and has the same electron configuration

48
Q

Why is it necessary to ionise molecules during TOF mass spectrometry?

A
  • ions can be accelerated by an electric field
  • so that it can be deflected by a magnetic field
  • so that it can be detected by a detector
49
Q

What is the formula used to find the mass of an ion/atom?

A

m= Aᵣ/1000 * L
L=avogadro’s constant
L=6.022 x 10²³

50
Q

What is the formula used to find the time of flight if you are given the mass of two ions (for mass spectroscopy)?

A

m₁/t₁²=m₂/t₂²

51
Q

What is the formula to find the mass of an atom/ion (mass spectrometry)?

A

2Eₖ * t²/d²=m

52
Q

Why must atoms be ionised to T.O.F mass spectrometry?

A

atoms must be ionised because:

  • only ions can be accelerated in an electric field
  • only ions can create a current in the detector
  • so they can be deflected/to bend beam
53
Q

Why is there a vacuum in the flight tube?

A

to ensure that ions travel at a constant speed (do not decelerate by colliding with air)

54
Q

How do you determine the number of atoms of a specific mass in a mass spectrometer?

A

by looking at the size of the current

55
Q

What is the definition of relative atomic mass?

A

it is the average mass of one atom compared to the mass of an atom of one C-12

56
Q

Why do particles with the same mass and velocity can be deflected by different amounts in the same magnetic field?

A

this could be because they have a different charge

57
Q

What does the amount that an ion is deflected depend on?

A

the lighter the ion, the more deflected it is

the higher the charge of the ion, the more deflected it is

58
Q

What is an orbital?

A

a region of space where an electron is likely to be found 90% of the time

59
Q

What are subshells?

A

shells are divided into subshells,

electrons in different subshells have different energies

60
Q

What are the four types of subshells?

A

s
p
d
f

61
Q

How many orbitals does an s subshell have?

A

1 orbital

maximum 2 electrons

62
Q

How many electrons can each orbital carry?

A

2 electrons per orbital

63
Q

How many orbitals does a p subshell have?

A

3 orbitals

max. 6 electrons

64
Q

How many orbitals does a d subshell have?

A

5 orbitals

max. 10 electrons

65
Q

How many orbitals does an f subshell have?

A

7 orbitals

max. 14 electrons

66
Q

What subshells exist in the first shell?

A

1s subshell

2 electrons in shell

67
Q

What subshells exist in the second shell?

A

2s, 2p

8 electrons in shell

68
Q

What subshells exist in the third shell?

A

3s, 3p, 3d

18 electrons in shell

69
Q

What subshells exist in the fourth shell?

A

4s, 4p, 4d, 4f

32 electrons in shell

70
Q

What are two exceptions to the orbital rule?

A

chromium and copper
they donate one of their electrons from the 4s subshell to the 3d subshell because they prefer a more stable full/half full subshell

71
Q

What is the rule for electrons filling in the 3rd and 4th shell?

A

have to fill in 4s subshell before filling up 3d subshell

72
Q

What is the electron configuration of Cr?

A

1s²2s²2p⁶3s²3p⁶3d⁵4s¹

not 3d⁴4s² as you might expect

73
Q

Using orbitals, explain why there is a drop IE between Mg and Al between group 2 and 3?

A

in aluminium, outer e⁻ is removed from the 3p subshell, which has a higher energy than the 3s subshell so it is further from the nucleus (as it has more energy) so reduced nuclear attraction
less energy required to remove outer electron

74
Q

Using orbitals, explain why there is a drop in ionisation energy between P and S?

A

in sulfur, there is one paired group of e⁻ in the 3p subshell, which causes repulsion between the paired e⁻ so less energy is required to remove electron from shared orbital

75
Q

Draw the mass spectrum for ³⁵Cl (75%) and ³⁷Cl (25%)?

A

peaks at 72, 74, 70
70 highest
72 2nd highest
74 lowest

76
Q

Why has Na a much lower first ionisation energy than neon?

A

This is because Na will have its outer electron in a 3s shell further from the nucleus and is more shielded. So Na’s outer electron is easier to remove and has a lower ionisation energy.

77
Q

Why does He have the highest first ionisation energy?

A

because its outer e⁻ are in the first shell closest to the nucleus so there is no shielding and the distance is less. Has a bigger IE than H because it has 2 protons (not one) so stronger nuclear force

78
Q

If chlorine exists as two isotopes, and hydrogen and carbon exist as one isotope
each, how many molecular ion peaks will be shown in the mass spectrum of C4H6Cl4?

A

5

79
Q

With this electron configuration: [Ar] 4s²3d³

how many outer electrons does this element have?

A

5

because 3d has more energy than 4s slightly so at a similar distance from the nucleus

80
Q

How can observations from reactions show that an element can exist in two oxidation states?

A

because 2 difference colours of solution will be displayed because each colour is due to each oxidation state

81
Q

Is the second ionisation energy larger than the first ionisation energy

A

yes, because the electron is being removed from a positive ion (not an atom) so the nuclear attraction is stronger, so more energy required
also the electron being removed is closer to the nucleus

82
Q

What can be adjusted in the mass spec. to enable ions formed by the different isotopes to be directed onto the detector?

A

electromagnet/electric field, magnet

83
Q

What is deflection (mass spectroscopy)?

A

when ions are deflected by a magnetic field

depends on the mass and charge of the ion on how much it has been deflected, same m/z ratio, same deflection

84
Q

What is the evidence for the max. no. of e⁻ that can be held in an s sub-level on the graph for IE across periods?

A

there are 2 elements before the drop in energy

85
Q

What evidence from the graph supports says that no more than three unpaired
electrons can be accommodated in the 3p sub-level?

A

drop in IE between P and S

86
Q

What is the relative isotopic abundance?

A

it is the proportion of each type of isotope present in the sample of the element naturally

87
Q

How do you calculate relative atomic mass from absolute mass?

A

absolute mass of one thing x 6.022x10²³

A-level AQA Chemistry (9 decks)

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