S1-L2 The structure of the Atom Flashcards
Outline the basic structure of an atom
- Electrons (-)
- Protons (+)
- Neutrons (uncharged)
How big is the atom compared to the nucleus?
-atom diameter 10, 000x larger than that of its nucleus
What is the charge of an atom?
- neutral
- -> e- loss gives charged ion
Briefly outline the nucleus of an atom
- centre of atom- almost all mass there
- atom’s protons & neutrons compose it
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
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
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
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
What is the “kinetic isotope effect”?
-heavier isotopes react slightly slower
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
Outline the main isotopes of carbon
- carbon-12 (6,6) stable
- carbon-13 (6, 7) stable
- carbon-14 (6, 8) radioactive
What are the isotopes of chlorine AND bromine?
- chlorine: 35 Cl/ 37 Cl
- bromine: 79 Br. 81 Br AND 23+ more unstable isotopes
Define Relative atomic mass (Ar)
-of an element is weighted average of individual isotopes
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
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
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
Outline the use of the two types of isotopes mentioned above
-Can use both forms as diagnostic AND tracer tools in research
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
