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CHEM1111 > Week 2 > Flashcards

Week 2 Flashcards

1
Q

as you go further down the periodic table…

A

the elements will become increasingly radioactive, nucleus is too big

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2
Q

Electrostatic (Coulomb) repulsion

A

The repulsion between protons acts to push these nucleons apart over a long range

Intended to make a nucleus radioactive, unstable

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3
Q

The strong nuclear force

A

a short range attraction between all nucleons
Make stable

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4
Q

Radioactivity 1: In nuclides with too few neutrons…

A

the electrostatic repulsion overwhelms the strong nuclear attraction

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5
Q

Radioactivity 2: As the nucleus gets larger…

A

the long-range electrostatic repulsion between protons accumulates and eventually overwhelms the strong nuclear attraction.

Nuclides with M > 208 (e.g. Uranium) are unstable

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6
Q

Radioactivity 3: When there are too many neutrons…

A

the nucleus is also unstable.

This is explained by a nuclear form of quantum theory, the Nuclear Shell Model

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7
Q

Noble gases are very stable because…

A

they have a complete shell

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8
Q

alpha decay

A

lose 2 protons and 2 neutrons

α particle is simply a helium nucleus with mass number 4 and charge 2+

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9
Q

beta decay

A

1 neutron lost and 1 proton gained

β(or β−) is an electron ejected from the nucleus. One neutron is changed into a proton in this nuclear reaction to balance the charge.

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10
Q

positron decay

A

1 neutron gained and 1 proton lost

β+ is a positron ejected from the nucleus. One proton is changed into a neutron in this nuclear reaction to balance the charge

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11
Q

electron capture

A

1 neutron gained, protons the same

Electrons fall into lower energy states to fill the vacancy left by the captured electron. A proton combines with the electron, forming a neutron.
Mass number stays the same

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12
Q

neutron emission

A

Simple emission of a neutron, which changes M but leaves Z unchanged.

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13
Q

gamma emission

A

No change in M or Z is associated with γ-emission on its own.

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14
Q

nuclear stability depends on…

A

size of nucleus
(there are no stable nuclei heavier than Pb w/ A=208 and Z=82)

N:Z ratio
(near to 1, but “bends” towards more neutrons per proton as the nucleus gets larger)

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15
Q

bad uses of radiation

A

Radiation sickness/burns
Cancer
Weapons

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16
Q

good uses of radiation

A

Cancer therapy
Medical imaging

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17
Q

radiation is…

A

high energy and produced by radioactive decay and causes ionisation of matter by ejecting electron from atoms

18
Q

the ionisation of a single molecule needs

A

10 eV

19
Q

how much energy in alpha radiation? (approx)

A

5 MeV

20
Q

how much energy in beta radiation? (approx)

A

1 to 0.05 MeV

21
Q

how much energy in gamma radiation? (approx)

A

1 MeV

22
Q

Why is radiation so bad for the body?

A

because the body is 50-70% water and reactions begin with water.

Water ionised to a cation and an electron

23
Q

Damage depends on 3 things…

A
  1. type of radiation
  2. length of exposure
  3. source of exposure
24
Q

internal exposure to radiation

A

Ingestion or inhalation. Alpha and beta are most dangerous. Most gamma radiation escapes the body

25
Q

external exposure to radiation

A

alpha and beta can’t penetrate through air and skin. Gamma radiation can penetrate skin - more dangerous

26
Q

Sievert (Sv)

A

unit that measures biological effect of radiation

27
Q

cancer therapy

A

Focusing ionising radiation onto the tumour
OR
Internal administration of a radiopharmaceutical

28
Q

Radiation for imaging

A

Uses radiation (gamma) emitted from within the body to map the body

Computer-assisted tomography can give 3D reconstruction of the body

28
Q

Technetium-99m imaging

A

Easily incorporated into many drugs
Easily prepared from Mo-99
Does not change its chemistry when it decays
Emits only highly-penetrating gamma rays, not harmful alpha/beta particles

29
Q

PET imaging

A

Uses radionuclide that emits positrons: positron emitters are proton rich

Within the body, positron reacts with an electron, producing two high energy gamma rays, which are detected outside the body

FDG is used to observe parts of the body that use high levels of glucose (tumours, brain etc.)

30
Q

Light (photoelectric effect)

A

Light is electromagnetic radiation that has both wave and particle (photons) nature.

The amount of energy (quantum) in each photon is determined by its frequency, ν (nu) or wavelength, λ (lambda).

31
Q

Black-body radiation

A

Proposed that energy is quantised:
E = hν (ν = frequency of oscillation, h = Planck’s constant)

32
Q

Spectroscopic lines

A

electrons in discrete orbits

Thus atom cannot lose energy continuously, but must do do in quantum jumps between different orbits

Light emitted by an excited atomic gas consists of discrete wavelengths, not a continuous band.

33
Q

Bohr model

A

postulated a set of circular orbits for electrons with specific, discrete radii and energies and that electrons could move in each orbit without radiating energy

34
Q

Energies for H

A

values between −ER (n = 1) and −ER/4 (n = 2) cannot be observed

as n increases, En approaches the energy of an unbound electron, or 0

35
Q

Problems with Bohr model

A
  1. According to classical physics, revolving charged particles radiate energy
  2. Bohr’s model could only explain the emission spectra of single-electron atoms. It failed to predict the spectra of multi-electron atoms.
  3. Bohr could offer no reason why an electron should have discrete orbits or energies.
36
Q

wavelength of a matter wave

A

λ=h/mv
m is mass
v is velocity
h is Planck’s constant

37
Q

Planck’s constant

A

6.626 x 10^-34 J s

38
Q

Mechanics of waves

A

Wave-behaviour + restricted motion lead automatically to discrete energy levels or frequencies.

Thus, the matter wave concept explains why electrons have discrete energy levels. No need for discrete orbits!

39
Q

Classical vs. quantum

A

quantum
- has large scale (goes to subatomic objects)
- wave is particles (dual nature)

CHEM1111 (15 decks)

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