- atoms with same atomic number BUT different mass number - ->or same n. of protons BUT different n. of neutrons - different atoms of same element - same n. of protons as e-'s - mass varies due to varying neutron number

S1-L2 The structure of the Atom Flashcards by Muazzam Ghani

Outline the basic structure of an atom

Electrons (-)
Protons (+)
Neutrons (uncharged)

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How big is the atom compared to the nucleus?

-atom diameter 10, 000x larger than that of its nucleus

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What is the charge of an atom?

neutral

- -> e- loss gives charged ion

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Briefly outline the nucleus of an atom

centre of atom- almost all mass there

- atom’s protons & neutrons compose it

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Define the following terms:

1-Nucleons
2-Atomic number (Z)
3-Mass number (A)

1- protons and neutrons
2- n. of protons in nucleus of atom
-sum of protons and neutrons in nucleus
–>AKA nucleon number

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Describe the electrons of an atom

surround nucleus–> occupy specific region in space-orbitals
orbitals grouped in to shells
->identified by principle quantum number, n= 1, 2, 3…each shells contains unique set of orbitals
completely filled shell v. stable–> noble gas
e-s determine atom properties like reactivity AND bond forming ability

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Define an isotope

atoms with same atomic number BUT different mass number
->or same n. of protons BUT different n. of neutrons
different atoms of same element
same n. of protons as e-‘s
mass varies due to varying neutron number

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Outline the following properties of isotopes:

1-chemical
2-physical

1- isotopes outer e- same AND same chemical identity so chemical properties identical
2-such as density can differ due to different mass of isotope

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What is the “kinetic isotope effect”?

-heavier isotopes react slightly slower

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What are the 3 main isotopes of hydrogen?

1H- most abundant isotope
2H- use in isotopic labelling experiments/ v. useful in NMR spectroscopy
3H- radioactive–>used in labelling experiments

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Outline the main isotopes of carbon

carbon-12 (6,6) stable
carbon-13 (6, 7) stable
carbon-14 (6, 8) radioactive

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What are the isotopes of chlorine AND bromine?

chlorine: 35 Cl/ 37 Cl

- bromine: 79 Br. 81 Br AND 23+ more unstable isotopes

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Define Relative atomic mass (Ar)

-of an element is weighted average of individual isotopes

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Example: 35 Cl and 37 Cl

What are their mass number?

35 Cl: P=17/ E= 17/ N=18
-> mass number is 35
37 Cl: P= 17/ E=17/ N=20
->mass number is 37

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Outline the composition of an ordinary chlorine atom and it’s measured atomic weight

ordinary composition is 3 35 Cl atoms and 1 37 Cl atoms

- ->so measured atomic weight is (3 x 35) + (1 x 37)/ 4 = 35.5

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What are “stable” and “unstable” isotopes?

Stable: remain unchanged indefinitely
Unstable: undergo spontaneous disintegration- to become stable nucleus
-> disintegration results in emission of small particles AND or radiation
also named as radioactive isotopes

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Outline the use of the two types of isotopes mentioned above

-Can use both forms as diagnostic AND tracer tools in research

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What is “mass spectrometry”?

measures molecular weight of atoms/ compounds via observation of m/z ratio of ions
works for both stable and unstable isotopes

What are the applications of mass spectrometry and how does this occur?

-determining isotopic abundance AND identity of small molecules + proteins and more
-atoms + molecules converted in to ions which can separate into ions which can separate on basis of their masses AND motions in
magnetic/electrical field

Example: Outline the features of the mass spectrum of neon-3 isotopes present

20 Ne/ 21 Ne/ 22 Ne
peak position gives atomic mass
peak intensity–> gives relative abundance
normally highest abundance scaled up to 100%
-> other values adjusted accordingly

Outline some of the uses of the following stable isotopes:

1- Ca-42, -44, -46, -48
2- C-13
3- Fe-54, -57, -58
4- O- 18

1-calcium metabolism/ bioavailability/ nutritional Ca role in pregnancy, growth AND development & lactation
2- molecular structure AND chemical reaction mechanism study
-molecular fingerprinting-dope testing athletes
3- metabolism/ energy expenditure studies
-metabolic tracer studies to identify genetic iron control mechanisms
4- studies of metabolism & energy expenditure
-lean body mass measurements
-obesity research

Define the term “radioactive decay”

nucleus of unstable radioisotope seeks energetic stability by emitting particles/ radiation
-> alpha/ beta AND gamma particles

What is “half life”?

t 1/2 (time to half) of radioactive isotopes

- -> time taken for activity set amount of radioactive substance to decay to half its original value

Outline and briefly explain the following mechanisms of radioactive decay

1- Alpha (a) radiation

1- Alpha particle emission

helium nuclei
(+) charged

2- Gamma (Y) Rays

2- Gamma photon emission - neutral - no effect on atomic mass/ number - often produced alongside a/ B particles- a or B decay leaves nucleus in excited state - -> then loses energy by Y emission - high frequency of EM radiation

3- Beta (B) Radiation

- 2 types: - -> beta (-) e- emission - -> beta (+) positron (anti-electron e+) emission

What is the "capture process"?

-small particle collides with nucleus AND added to it

Outline "neutron capture"

239Pu + 1--> 240Pu --> 241Am | 94 0 94 95

Describe the "boron neutron capture theory"

10 B + 1 n --> 7 Li + 4 He | 5 0 3 2

What is the radiation penetrating power of alpha/ beta and gamma radiation

- alpha- cant penetrate past paper - beta- unable to penetrate past aluminium - gamma- unable to penetrate past lead

What is "Xofigo"?

-isotope medication used to treat prostate cancer which spread to the bones

Why is xofigo administered by injection?

-Half-life of Radium-223 in xofigo short so when patient injected Radium-223 able to quickly reach bone where cancer spread to

Why is Ra suitable to treat bone metastasis?

-Radium-223 mimics calcium found in bones

Which steps in decay chain of Ra-223 involve in alpha-emission?

6 steps: 1) Ra (223) --> Rn (219) --> Po (215)--> Pb (211) 2) At (215)--> Bi (211)--> Ti (207) 3) Po (211)--> Pb (207)

Outline the application of unstable isotopes in the following categories: 1- Industrial

1- energy generation - food & medical supply sterilisation (usually 60 Co-Cobalt) - imaging AND gauging

2- Medical

2- diagnostic | -therapeutic--> weakening/ destroying particular targeted cells

3- Domestic

3- smoke detectors--> use 241 Am

What is "imaging"?

- Radioisotopes used for diagnosis must emit gamma rays of sufficient energy to escape from body - -> must have half-life short enough for it to decay away soon after imaging complete

Outline the use of the following common radioisotopes: ``` 1- 99^ Tc ^ m 2- thallium-201 chloride 3- 82 ^Rb/ 99^Tc^m 4- 18^F -Fluoro-deoxy glucose (FDG) 5-other 18^F- compounds ```

1- t 1/2 6 hours/ emit Y and low energy B particles/ produced on site in generator 2- myocardial perfusion imagine (MPI) 3- detection AND prognosis of coronary artery disease 4- often used for PET imaging which has half-life of 110 min--> to measure cell metabolism 5- image DNA synthesis AND hypoxia -->condition where region of body deprived of O2 supply at tissue level

Define and describe the term "therapy"

- Selective damage to unhealthy tissue - radioisotope used for therapy should be strong B emitter to damage cells in small area - Y emission allows imaging too

What is the application of radisotopes?

-can implant near tumor (brachytherapy)/ injected with selective uptake

Outline the following commonly used radioisotopes for therapy 1-Radioiodine: 132^I/ 131^I 2- 89^SrCl and 153 Sm 3- 32^P 4- Lutetium- 177/ Yttrium-90

1- 132^I for diagnostics 131^I for overreactive thyroid/ thyroid cancer treatment -131^I half life--> 8.02 days AND decays by B and Y emission 2- B emission t 1/2 1.93 day- bone metastasis (spread of cancer from original site to bone) 3- B emission AND half-life 14.28 days --> control of red blood cell production in bone marrow in polycythemia vera 4- multiple uses- conjugated (reversibly combined substance) to peptide OR antibodies like Zevalin in sealed source brachytherapy (involves placing radioactive material inside body to treat cancer)

Summary of lecture

- Atom- comprised of nucleus (protons AND neutrons) & surrounded by e-'s - isotopes- atoms of same atomic number BUT different atomic mass - stable + unstable isotopes - isotopes in medicine - mass spectrometry