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A-LEVEL CHEM > PHYSICAL CHEM - ATOMIC STRUCTURE > Flashcards

PHYSICAL CHEM - ATOMIC STRUCTURE Flashcards

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1
Q

What is the diameter of the nucleus?

A

approx 10^-15 m

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2
Q

What is the diameter of an atom?

A

approx 10^-10 m (~100000x the diameter of the nucleus)

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3
Q

What is the relative charge of a proton?

A

+1

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4
Q

What is the relative charge of a neutron?

A

0

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5
Q

What is the relative charge of an electron?

A

-1

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6
Q

What is the relative mass of a proton?

A

1

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7
Q

What is the relative mass of a neutron?

A

1

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8
Q

What is the relative mass of an electron?

A

1/1840

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9
Q

Why do protons not repel each other in the nucleus?

A

protons and neutrons are held together by strong nuclear force which is strong enough to overcome the repulsion between protons in the nucleus

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10
Q

What are isotopes?

A

atoms of the same element with the same no. of protons but a diff no. of neutrons

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11
Q

How can we use isotopes for carbon dating?

A
  • some isotopes are unstable and radioactive. they become stable by emitting radiation over time
  • this means that we can use the amount of an isotope in an object to work out how old it is
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12
Q

What are the 4 types of sub-shell?

A
  • s
  • p
  • d
  • f
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13
Q

How many orbitals does each subshell contain?

A
  • s: 1
  • p: 3
  • d: 5
  • f: 7
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14
Q

How many electrons can each orbital hold?

A

2

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15
Q

What is the Aufbau principle?

A

orbitals with the lowest energy are filled up first

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16
Q

What is the Pauli exclusion principle?

A

each orbital can only hold 2 electrons and they must have opposite spins

17
Q

What is Hund’s rule?

A

electrons fill orbitals separately before they start sharing

18
Q

Which orbital is filled first: 3d or 4s? why?

A

4s - lower in energy than 3d

19
Q

What 2 elements are exceptions to the rules when filling up orbitals and why?

A
  • copper - only fills 1 electron in the 4s orbital allowing 10 to go into the 3d orbital in order to have a more stable configuration
  • chromium - only fills 1 electron in 4s and 5 go into 3d because 5 single electrons in each d orbital is more stable
20
Q

What is ionisation energy?

A

the energy required to remove 1 mole of electrons from a mole of atoms in the gaseous state (measured in KJ mol ^-1)

21
Q

What is the trend in first ionisation energy down a group?

A

IE decreases

22
Q

Explain why ionisation energies decrease when you go down a group?

A
  • increase in shielding
  • increase in distance of outer electron
  • less attraction between outer electron and nucleus
23
Q

What is the trend in first ionisation energy across a period?

A

IE increases

24
Q

Explain why ionisation energies increase when you go down a group?

A
  • increased nuclear charge
  • greater force of attraction between nucleus and outer electron
  • same amount of shielding
25
Q

Why is it easier to remove an electron from Al than Mg?

A
  • outer electron in Al is in 3p orbital, outer electron in Mg is in 3s orbital
  • 3p orbital is slightly higher in energy than 3s orbital
26
Q

Why is it easier to remove an electron from S than from P?

A
  • outer electron in S is paired with another electron
  • it is easier for S to lose one electron due to repulsion between paired electrons
27
Q

What is a mass spectrometer?

A

accurate scientific instrument used to determine relative isotopic mass and isotopic abundance (these values are then used to calculate RAM)

28
Q

What are the uses of ass spectrometry?

A
  • carbon-14 dating
  • detecting illegal drugs
  • forensic science
28
Q

What are the 4 stages of mass spectrometry?

A
  • ionisation
  • acceleration
  • ion drift in flight tube
  • detection
29
Q

Electrospray ionisation

A
  • sample dissolved in volatile solvent and pushed through needle at high pressure
  • high voltage applied causing each atom to gain a proton (H^+ ion)
  • X (g) + H^+ –> XH^+ (g)
30
Q

Electron impact ionisation

A
  • sample is vaporised
  • high energy electron fired at sample to knock one electron off of each particle
  • X (g) –> X^+ + e^-
31
Q

What happens during the 2nd step of mass spectrometry?

A
  • acceleration
  • +vely charged ions accelerated by electric field so they all have the same Ek
32
Q

What happens during the 3rd step of mass spectrometry?

A
  • ion drift in flight tube
  • ions enter region with no electric field so they drift
  • lighter ions drift faster than heavier ions therefore heavier ions take longer to reach the detector
33
Q

What happens during the 4th step of mass spectrometry?

A
  • detection
  • ions reach detector (-ve plate) and generate a small current (produced by e^- transferring from -ve detector to +ve ions)
  • current size is proportional to abundance of isotope
34
Q

What is a mass spectrum?

A

plot of relative abundance against mass : charge ratio (m/z)

35
Q

How do you calculate time of flight?

A

TOF (s) = length of flight tube (m) x √ ( mass (kg) / 2 x kinetic energy (J)) t = d√(m/2Ek)

A-LEVEL CHEM (6 decks)

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