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Physical Chem A lvl > Atomic Structure > Flashcards

Atomic Structure Flashcards

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1
Q

What is mass spectrometry?

A

A method to determine the mass of atoms or molecules

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2
Q

What can mass spectrometry be used for?

A
  • finding relative isotopic abundance
  • molecular mass
  • helping determine the structure of a compound
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3
Q

What is stage 1 of mass spectrometry if the sample is NOT a large molecule?

A

Ionisation
- fire high-energy electrons from an electron gun
- this knocks off electrons of each particle to make it a 1+ ion

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

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4
Q

What is stage 1 of mass spectrometry if the sample IS a large molecule?

A

Electrospray ionisation
- The sample is dissolved in a volatile solvent (like water) and injected through a fine hypodermic needle to give a fine mist (aerosol)
- The tip of the needle is attached to a positive terminal of a high-voltage power supply
- Particles are ionised by gaining a proton (H+) from the solvent

M + H+ —> MH+

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5
Q

What is the equation in electrospray ionisation and what does MH+ stand for?

A

M + H+ —> MH+

MH+ is whats detected, the mass of this is recorded and will be the Mr of the substance + 1

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6
Q

What’s the 2nd stage of mass spectrometry?

A

Acceleration

  • Positive ions are accelerated with an electric field (a negatively charged plate)
  • Regardless of mass, all particles will have the same amount of kinetic energy
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7
Q

What’s the 3rd stage of mass spectrometry?

A

Flight Tube

  • All the particles will have different velocities (due to their different masses) so we can use this to differentiate between them
  • This is because velocity affects the time of flight of each particle
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8
Q

What’s the 4th stage of mass spectrometry?

A

Detection

  • The positively charged ions hit a negatively charged plate
  • They gain an electron, causing an electric current
  • The electric current is measured, and the size gives a relative measure of the number of specific ions hitting the plate.
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9
Q

What’s the equation for Kinetic energy?

A

Ke=1/2mv^2

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10
Q

In summary, what are the 4 stages of Mass spectrometry?

A
  • Ionisation
  • Acceleration
  • Flight Tube
  • Detection
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11
Q

What must we do to the sample before starting mass spectrometry?

A

Vapourise it

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12
Q

What was the first model of the atom?

A

Dalton 1803
- Atoms are tiny solid spheres which cant be divided

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13
Q

What was the second model of the atom?

A

Thompson 1897; Plum pudding model
- Electron discovered
- Positive ball of charge with atoms embedded

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14
Q

What was the third model of the atom?

A

Rutherford 1911; Nuclear Model
- Alpha particles (He2+) fired at gold atoms ( some deflected and bounced back, most passed through)
- Small positively charged nucleus, most of the mass found here
- Electrons orbit the nucleus, mostly empty space though

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15
Q

What was the fourth model of the atom?

A

Bohr 1913
- Electrons found in shells at certain distances surrounding the nucleus

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16
Q

When was the proton discovered and by who?

A

Rutherford 1917

17
Q

What was the last model of the atom?

A

Chadwick 1932
- Neutrons discovered and located in the nucleus

18
Q

Things to look out for when looking at a mass spectrometer graph?

A
  • Don’t assume that m/z is mass all the time, there could be unexpected peaks due to 2+ charges (will be 1/2 the mass)
  • Relative abundance isn’t always a %
19
Q

Bromine has 2 isotopes at m/z = 79 and 81, how many peaks would you expect and why? What about their heights?

A

5, for 5 different combinations.
Since Bromine is diatomic, we can add them tg asw to make Br2.
Br: 79, 81
Br2: (79+81=160), (79+79=158), (81+81=162)
The 160 peak would be double in height since there are 2 ways of making 160 (79+81) and (81+79). because the ratio of abundance of 158, 160 and 162 is 1:2:1.

20
Q

How would you label the peak for an isotope of Br2, when Br has peaks at m/z=79 and 81 (the species)

A

You would label at 160, [79Br 81Br], you would label at 158 [79Br2], at 162 it would be [81Br2]

21
Q

What is the first ionisation energy trend along a period?

A

Energy increases
- Decreasing atomic radius (electrons are added to the same shell but more protons in the nucleus pull electrons in the shells closer)
- Increasing nuclear charge (more protons)
- Sheilding satys the same
These factors increase the electrostatic forces of attraction

22
Q

How would you calculate the mass of oxygen, knowing’s it’s Ar is 16?

A

16/6.022x10^23

23
Q

What do isoelectronic species have in common?

A

Their electron configurations

24
Q

What is the first ionisation energy?

A

The energy required to remove one electron from each atom in a mole of gaseous atoms, producing one mole of 1+ gaseous ions

25
Q

Where does the evidence for how electrons are arranged in atoms come from?

A

Ionisation energies

26
Q

What is ionisation energy measured in?

A

kJmol-1

27
Q

What’s the equation for the 1st ionisation energy of Na?

A

Na(g) —> Na+(g) + e-

28
Q

What’s the equation for the 2nd ionising energy of Na?

A

Na+(g) —> Na2+(g) + e-

29
Q

What is the first ionisation energy trend down a group?

A

First ionisation energy decreases
- Atomic radius increases
- Shielding increases (electrons in shells cause repulsion between electron and nucleus)
Weakens the electrostatic forces of attraction

30
Q

Why do group 3 elements have a lower first ionisation energy than group 2?

A

Group 2 loses an electron from the s orbital whereas group 3 loses an electron from the p orbital. Since the p orbital has more energy than s, it’s easier to lose an electron from it.

31
Q

Why do group 6 elements have a lower first ionisation energy than group 5?

A

In group 6, this is the first element in the period that there are paired electrons in the _P orbital. These repel each other, meaning less energy is required to remove one of them.

32
Q

What is the electronic configuration of Cr?

A

Cr:1s2 2s2 2p6 3s2 3p6 4s1 3d5

33
Q

What is the electronic configuration of Cu?

A

Cr:1s2 2s2 2p6 3s2 3p6 4s1 3d10

34
Q

Why is the first ionisation energy of neon lower than the third ionisation energy of magnesium?

A

Mg2+ and Ne have the same amount of electrons but
- Mg2+ has more protons (bigger nuclear charge)
- This means the IONIC radius decreases

35
Q
A

Physical Chem A lvl (7 decks)

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