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AS Chemistry - Physical > 3.1.1 - Atomic Structure > Flashcards

3.1.1 - Atomic Structure Flashcards

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1
Q

What holds protons and neutrons close together in the nucleus of an atom?

A

The ‘strong nuclear force’

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2
Q

What attracts electrons to the nucleus of an atom?

A

Electrostatic forces of attraction between negative electrons and positive protons

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3
Q

Which is stronger, the force that holds protons and neutrons close together in the nucleus of an atom, or what attracts electrons to the nucleus of an atom?

A

The ‘strong nuclear force’ between protons and neutrons in the nucleus

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4
Q

Why do protons not leave the nucleus towards the electrons?

A

The ‘strong nuclear force’ is stronger than the electrostatic forces of attraction between negative electrons and positive protons

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5
Q

The force that holds protons and neutrons close together in the nucleus of an atom only works over ______ distances (e.g. ?)

A

The ‘strong nuclear force’ only works over short distances, e.g. within the nucleus

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6
Q

What is the relative mass of an electron?

A

1/1840

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7
Q

What is the relative mass of a proton and neutron?

A

1

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8
Q

Define atomic number, Z

A

The number of protons in the nucleus of an atom

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9
Q

Define mass number, A

A

The number of protons AND neutrons in the nucleus of an atom

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10
Q

Define ‘isotope’

A

The same number of protons but different number of neutrons in the nucleus

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11
Q

Do isotopes of an element react in the same way?

A

Yes (same electron configuration and number)

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12
Q

Do isotopes of an element have the same mass numbers?

A

No - mass no. is number of protons AND neutrons in the nucleus of an atom, and no. of neutrons changes between isotopes

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13
Q

Why do two paired electrons in the same orbital repel each other?

A

Due to opposing spins

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14
Q

What does an s orbital look like?

A

(Spherical)

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15
Q

What does a p orbital look like?

A

(Paired)

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16
Q

What does a d orbital look like?

A

(Double)

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17
Q

Rules of electron configurations? (x2)

A

1 - Build up from the lowest to highest energy levels

2 - Fill orbitals singly before pairing (as to avoid repulsion)

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18
Q

Define ‘ionisation energy’

A

The amount of energy required to remove one electron from each atom of one mole of gaseous atoms, to form one mole of gaseous +1 ions

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19
Q

Unit of ionisation energy?

A

kJ mol^-1

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20
Q

Trend in ionisation energy across a period?

A

INCREASES

  • Atomic radii decrease
  • Same energy level/same shielding effectively
  • Nuclear charge INCREASES
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21
Q

Trend in ionisation energy down a group?

A

DECREASES

  • Atomic radii increase
  • More energy levels/greater shielding
  • Nuclear charge stays same
22
Q

Why does the IE decrease between Mg and Al, going across period 3 from left to right?

A

Mg: 1s2, 2s2, 2p6, 3s2
-> Al: 1s2, 2s2, 2p6, 3s2, 3p1
So the electron from aluminium is removed from the 3p sub-shell, which has a higher energy level and thus requires less energy to remove

23
Q

Why does the IE decrease between phosphorous (P) and sulphur (S), going across period 3 from left to right?

A

P: 1s2, 2s2, 2p6, 3s2, 3p3
S: 1s2, 2s2, 2p6, 3s2, 3p4
In S, there is electron pairing in the 3p orbital, so the electrons have opposite spin and repel each other, thus the electron in S requires less energy to remove than that in P - despite increased nuclear charge

24
Q

What evidences the existence of p,s,d sub-shells?

A

The IE decrease between phosphorous (P) and sulphur (S), going across period 3 from left to right, due to electron pairing in sub-shells and repulsion

25
Q

What is mass spectrometry useful for?

A

Determination of an atom’s relative atomic mass (Ar)/a molecule’s relative molecular mass (Mr)

26
Q

Define Ar (relative atomic mass)

A

Ar = mean mass of 1 atom/ (1/12 mass of 1 atom of 12C)

27
Q

Define Mr (relative molecular mass)

A

Mr = mean mass of 1 molecule/ (1/12 mass of 1 atom of 12C)

28
Q

What are the five stages of time of flight mass spectrometry?

A 
Ionisation
Acceleration
Deflection
Drift
Detection
29
Q

Why does ToF MS occur in a vacuum?

A

So charged particles do not collide with other molecules in the air (impacting flight time)

30
Q

What happens in acceleration in ToF MS?

A

All ions are accelerated by an electrical field to have equal kinetic energy. Ions are accelerated into a finely focused beam

31
Q

What happens in deflection in ToF MS?

A

Ions are deflected by a magnetic field, dependent on their m/z ratio

32
Q

Deflection in ToF MS

  • Lighter ion?
  • More charge?
A
  • Lighter ion = greater deflection
  • More charge = greater deflection
    The higher m/z ratio, the greater the deflection
33
Q

If an ion has a mass of 56 and a charge of +2, what is its m/z ratio?

A

m = 56
z = 2
so 56/2 = 28 = m/z

34
Q

What happens at the ion detector?

A

Ion hits the detector and picks up an electron (becoming neutrally charged again), causing an electrical current to flow

35
Q

A small m/z leads to lots of deflection. How can you reduce this?

A

Use a smaller magnetic field

36
Q

A high m/z leads to little deflection. How can you increase this?

A

Use a larger magnetic field

37
Q

Using a mass spectrum, how do you calculate the Ar of an atom?

A

Ar = sum of abundance x mass/ total abundance

38
Q

What is the molecular ion peak and what is it equal to?

A

M+ formed when one electron is removed from the molecule. Equal to the Mr of the molecule

39
Q

What are the isotopes of chlorine and their ratio to each other?

A

Chlorine- 35 and chlorine- 37

3:1

40
Q

Why does the mass spectrum of a chlorine MOLECULE have three peaks?

A

3 possible types of the chlorine molecule can be formed:
35 + 35 = 70 (m/z)
35 + 37 = 72
37 + 37 = 74

41
Q

What is the abundance on the mass spectrum of each of the 3 possible types of the chlorine molecule that can be formed?

A

35 + 35 = 70
3/4 x 3/4 = 9/16 = 56% abundance

35 + 37 = 72
3/4 x 1/4 = 3/16 = 19% abundance

37 + 37 = 74
1/4 x 1/4 = 1/16 = 6.25% abundance

42
Q

What are the two types of ionisation in ToF MS?

A

Electrospray ionisation and electron impact ionisation

43
Q

Describe electron impact ionisation x4

A
  • Sample is vaporised
  • High energy electrons are fired at it, from an ‘electron gun’ (a hot wire filament with a current running through it that emits electrons).
  • This knocks off one electron from each particle forming a 1+ ion.
  • The 1+ ions are then attracted towards a negative electric plate where they are accelerated.
44
Q

Describe electrospray ionisation x4

A
  • Sample is dissolved in a volatile solvent (eg water or methanol)
  • Sample injected through a fine hypodermic needle to give a fine mist (aerosol).
  • The tip of the needle is attached to the positive terminal of a high-voltage power supply, so the particles are ionised by gaining a proton
  • The solvent evaporates away while the XH ions are attracted towards a negative plate where
    they are accelerated.
45
Q

General equation in electrospray ionisation?

A

X(g) + H+ -> XH+(g)

46
Q

General equation in electron impact ionisation?

A

X(g) -> X+(g) + e–

47
Q

When do we generally use electron impact ionisation?

A

For element/ substances with low formula mass

48
Q

When do we generally use electrospray ionisation?

A

Substances with higher molecular mass including many biological molecules such as proteins

49
Q

With which ionisation technique is fragmentation more likely to occur?

A

Electron impact ionisation

50
Q

Detection: the size of the current gives a measure of what?

A

The number of ions hitting the plate.

AS Chemistry - Physical (8 decks)

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