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Physical chemistry > (physical) 3.1.1 atomic structure > Flashcards

(physical) 3.1.1 atomic structure Flashcards

1
Q

What can differ in a isotope ?

A

physical properties (such as density )

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2
Q

what is mass spectrometry ?

A

instrumental method of analysis used to :
- to find the mass of each isotope and percentage (abundance) of each isotope in a sample to determine relative atomic mass
- find the relative molecular mass of substances made of molecules

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3
Q

What are the 4 main stages of ToF mass spectrometry ?

A
  • ionisation
  • acceleration
  • flight tube
  • detection (ion)
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4
Q

What are the 2 types of ionisation ?

A
  • electron impact ionisation (electron ionisation )
  • electrospray ionisation
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5
Q

What is the method for electron impact ionisation ( electron ionisation ) ?

A
  • sample is vapourised
  • high energy electrons are fired at it with the use of an electron gun
  • This allows an electron to be knocked off from each particle forming 1+ ions
  • 1+ ions attracted to a negative electric plate where they are accelerated
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6
Q

What is the general equation for electron impact ionisation ?

A

X (g) —–> X+ (g) + e-
e.g
Mg (g) —–> Mg+ (g) + e-

(g) means gas

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7
Q

What is the method for electrospray ionisation ?

A
  • sample is dissolved in a volatile solvent
  • injected through hypodermic needle at high pressure to produce a fine mist (aerosol)
  • high voltage applied to needle
  • particles ionised by gaining a proton (H+ ion ) from the solvent as they leave the needle producing XH+ ions
  • solvent evaporates and XH+ ions are attracted towards a negative plate where they are accelerated
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8
Q

What is the general equation for electrospray ionisation ?

A

X(g) + H+ —–> XH+ (g)

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9
Q

Stage 2 - acceleration (what is the method? )

A
  • positive ions are accelerated by electric field
  • all ions have the same kinetic energy
  • ions with lower mass/charge ratio experience greater acceleration (lighter so accelerate more quickly )
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10
Q

in stage 2 - acceleration of ToF mass spectrometry why are the ions accelerated using a electric field ?

A

so that they have the same kinetic energy

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11
Q

What does the velocity of each particle depend on

A

The mass

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12
Q

What velocity do lighter particles have ?

A

faster velocity as they have less mass

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13
Q

What velocity do heavier particles have ?

A

slower velocity as they have more mass

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14
Q

What equation would be used for acceleration ?

A

KE = 1/2 mv^2
(rearrange to find velocity, given in exam )

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15
Q

What is kinetic energy (KE) measured in ?

A

J (joules)

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16
Q

What is mass (m) measured in ?

A

kg

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17
Q

What is velocity (v) measured in ?

A

m s ^-1

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18
Q

What is stage 3 in Tof mass spectrometry ?

A

Flight tube

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19
Q

What is the method for flight tube ?

A
  • positive ions travel through a hole in the negatively charged plate into the tube .
  • Time of flight depends on velocity
  • The velocity depends on the mass
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20
Q

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

A

t = d/v
then substitute v with the rearranged formula of KE = 1/2mv^2

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21
Q

what does t stand for and what is its unit ?

A

t = time of flight ( s )

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22
Q

What does d stand for and what is its unit ?

A

d = length of flight tube (m)

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23
Q

What does v stand for and what is its unit ?

A

v = velocity of particle (m s^-1)

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24
Q

What does m stand for and what is its unit ?

A

m = mass of particle (kg)

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25
Q

What does KE stand for and what is its unit ?

A

KE = kinetic energy of particle (J)

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26
Q

What does the ToF along flight tube equation show ?

A

It shows ToF is directly proportional to the square root of the mass of the ions

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27
Q

If ToF is directly proportional to the square root of the mass of the ions what does this mean ?

A
  • lighter ions travel faster and reach detector in less time - heavier ions move slower and take longer to reach detector
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28
Q

What is stage 4 in ToF mass spectrometry ?

A

Detection

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29
Q

What is the method for detection ?

A
  • positive ions hit the detector
    -when they hit the plate the positive ions are discharged by gaining electrons from the plate
  • this generates a movement of electrons and an electric current gives a measure of the number of ions hitting the plate
  • size of current (charge) is proportional to the abundance of the ions
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30
Q

What does the mass spectrum show ?

A

the mass to charge ratio (m/z) and the relative abundance of each ion

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31
Q

What does mass spectrometry tell us ?

A

mass of each isotope and percentage (abundance) of each isotope in a sample to determine relative atomic mass

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32
Q

how would you calculate relative atomic mass?

A

mass times abundance / 100

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33
Q

if there is a mass spectrum produced via electron impact ionisation what would a high m/z value mean ?

A

Its value is from the molecular ion and its m/z value gives the relative molecular mass

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34
Q

if there is a mass spectrum produced via electron impact ionisation why are there small peaks (low m/z ratio) ?

A
  • Due to fragmentation (main answer)
  • due to molecular ions that contain different isotopes
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35
Q

what does the position of the peak on a mass spectrum show ?

A

relative atomic mass

36
Q

what does the peak height in a mass spectrum show ?

A

relative isotopic abundance (relative amount of each isotope )

37
Q

What is an orbital ?

A

region in which an electron can be found

38
Q

how many electrons can each orbital hold ?

A

up to 2 electrons as long as they have opposite spin

39
Q

What is Pauls Exclusion principal ?

A

orbitals can hold up to 2 electrons as long as they have opposite spin .

40
Q

What are the 4 different shapes of orbitals ?

A

s , p ,d ,f

41
Q

What shape are S orbitals ?

A

spherical

42
Q

How many sets do S orbitals come in ?

A
  • it comes in sets of one (can hold 2 electrons )
  • one occurs in every principal energy level
43
Q

What shape are P orbitals ?

A
  • dumbbell shaped
44
Q

How many sets do P orbitals come in ?

A
  • come in sets of 3 ( can hold up to 6 electrons)
  • 3 occur in every principal energy level except the first
45
Q

What shape are d orbitals ?

A
  • various shapes
46
Q

How many sets do d orbitals come in ?

A
  • come in sets of 5 (can hold up to 10 electrons )
  • five occur in energy levels except the first and second
47
Q

How many sets do f orbitals come in ?

A
  • come in sets of 7 (can hold up to 14 electrons)
  • 7 occur in each energy level except first ,second and third
48
Q

What orbital does the first energy level contain ?

A

s orbital (1s)

49
Q

What orbitals does the second energy level contain ?

A

s orbital and 3 p orbitals labelled 2s and 2p

49
Q

What orbitals does the third energy level contain ?

A
  • s orbital , 3 p orbitals and 5 d orbitals
  • labelled 3s , 3p and 3d
50
Q

What orbitals does the fourth energy level contain ?

A
  • s orbital , 3 p orbitals , 5 d orbitals and 7 f orbitals
  • labelled 4s , 4p , 4d and 4f
51
Q

What is the order in which orbitals are filled ?

A

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 4d, 4f

  • note : 4s is before 3d
52
Q

What kind of arrows are used to indicate electrons ?

A

half arrows

53
Q

What are the 2 elements that don’t follow the orbital rule?

A

Cu (copper) and Cr (chromium )

54
Q

What is the key fact about the electronic structures of Cu and Cr ?

A

The electronic structures are more stable than alternative structures that follow the pattern

55
Q

What is different about the electronic configuration of Cr and Cu ?

A

As they fill the 3d shell before the 4s shell
e.g
Cr - 1s^2 , 2s^2 , 2p^6 , 3s^2 , 3p^6 , 4s^1 ,3d^5

  • if it followed pattern it would have been 4s^2 and 3d^4
56
Q

What happens to the electronic configuration of transition metals when they form ions ?

A

They lose the 4s electrons before the 3d electrons

57
Q

What does measuring ionisation energies tell us ?

A

provides evidence that electrons are arranged in shells or energy levels

58
Q

What is the meaning of ionisation energy ?

A

measure of the amount of energy needed to remove electrons form atoms

59
Q

What is the meaning of first ionisation energy ?

A

energy needed to remove one mole of electrons from one mole of gaseous atoms.
(to form one mole of gaseous positive ions )

60
Q

What is the equation that illustrates the process of first ionisation energy ?

A

X(g) –> X+ (g) + e-

61
Q

What does the value of the first ionisation energy depend on ?

A

electronic structure

62
Q

What is the general trend across period 3 ?

A

General increase in 1st ionisation energy

63
Q

Why does nuclear attraction increase in period 3 ?

A

because successive elements have a bigger nuclear charge and the same shielding

64
Q

In period 3 why is there a dip from Mg to AI ?

A
  • because Mg is losing 3s electron , AI is losing 3p.
  • 3p is higher in energy so easier to remove due to increase shielding and increase distance
  • if they have more energy less energy is required to remove
65
Q

Why is there a dip from P to S (period 3 ) ?

A
  • because repulsive force between the two paired up electrons (opposite spin ) in S makes electrons easier to remove than P

note : S has opposite spin so more energy so less energy needed to remove

66
Q

What do the dips provide evidence for ?

A

electrons being arranged in sub levels (sub- shells )

67
Q

What happens when there are filled inner shells ?

A

exert a shielding effect which lowers the effective nuclear pull

68
Q

What happens when the electrons are further away from the nucleus ?

A

lower nuclear attraction for an electron
- nuclear charge stays the same but due to shielding it is felt less

69
Q

What is the trend down group 2 ?

A
  • 1st ionisation energy decreases down group 2
70
Q

Why does 1st ionisation energy decrease down group 2 ?

A
  • with each successive element there is an extra electron shell
  • so the outer electron is further from the nucleus and more shielded.
  • increased nuclear charge outweighed by greater shielding and distance
71
Q

What does the decrease down group 2 prove ?

A

evidence for electrons being arranged in energy levels (shells )

72
Q

What is the trend down group 1 ?

A

value decreases down group 1

73
Q

Why is the outer s electron easier to remove in group 1 ?

A

despite increased nuclear charge as you go down group the outer s electron is easier to remove due to increase shielding and greater distance from the nucleus - outer electron held less strongly so easier to remove

74
Q

What factors cause a increase in ionisation energy ?

A
  • similar distance
  • similar shielding
  • increase nuclear charge
75
Q

What factors cause a decrease in ionisation energy ?

A
  • starting a new orbital ( s to p ) - cause decrease because e.g. 2p has more energy than 2s2 so less energy is required to remove
  • due to opposite spin - if they have opposite spin they have more energy so require less energy to remove
  • new shell - increase shielding and distance
76
Q

What is the meaning of successive ionisation energies (2nd I.E) ?

A
77
Q

What is the equation that illustrates the process of successive I.E (2nd I.E)?

A

X+(g) –> X^2+ (g) + e-

78
Q

Why do successive ionisation energies get bigger ?

A
  • Because there are fewer electrons and the same number of protons
  • The remaining electrons are held more tightly by the unchanged nuclear charge
79
Q

When do large increases (jumps ) occur in successive I.E ?

A

When there is a change of shell

80
Q

Why do large increases (jumps ) occur ?

A

when going to one energy level (shell ) to another The jump occurs because the new energy level is closer to the nucleus so there is a big decrease in shielding

81
Q

What can large increases be used to predict in successive I.E ?

A

group of unknown element

82
Q

Why are cations always smaller than corresponding atoms ?

A
  • cations ( lose electrons ) contain fewer electrons than their parent atoms, while having same nuclear charge .
    Meaning they have a stronger attraction that pulls the remaining electrons closer to the nucleus
83
Q

Why are anions always larger than corresponding atoms ?

A
84
Q

What is nuclear charge ?

A

Total charge of the nucleus which is equal to the number of protons in nucleus
- doesn’t decrease with increase of shells

85
Q

How does the shielding and distance affect nuclear charge ?

A
  • shielding prevents the outer electron shell to feel the full positive charge of nucleus (nuclear charge does not change but is felt less )
  • the increase in distance means that nuclear charge is felt less as there is more shielding
86
Q

When does nuclear charge increase ?

A
  • across a period
  • because there is an increase number of protons meaning an increase in effective nuclear charge of the atoms

Physical chemistry (2 decks)

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