Elements of Life Flashcards
Explain what is meant by half life
time taken for half a radioactive isotope to decay
Suggest why it is not advisable to use an isotope with either a very short or a very long half-life as a medical tracer.
short - would not be around in sufficient levels to detect.
long - possible to harm the patient
Why did Mendelev leave gaps in the periodic table
For elements to be discovered
How did later evidence from the scientific community support Mendeleev’s decision to leave gaps in his Periodic Table?
New elements were found that showed properties that fitted in with the groups
Which group in the modern Periodic Table is missing from Mendeleev’s table?
Group 8/0
How do you measure the volume of gas
find out how many moles of the substance there is and times it 24000
What is entropy
The measure of disorder
A fossil has a count rate of 12.5%. How many half lifes has it had
3
Name 2 assumptions that have to be made when calculating half life by count rate
half life unaffected by temperature or pressure
No loss or gain of radioisotope
Name two observations when calcium reacts with water
Gas is given off and the calcium dissolves
What information is given by the height of the peak in mass spec
The relative abundance
State the radioactive decay that turns hydrogen-3 into helium-3. Explain your answer
beta decay, where one neutron is converted into a proton
Suggest why high temperature and pressure are need for nuclear fusion
Needs to overcome the repulsion of the two positively charged nuclei
Describe the appearance of an atomic absorption spectrum
Black lines of a coloured background
Describe the appearance of an atomic emission spectrum
Coloured lines on a black backgrouns
Explain in terms of electronic levels, why the absorption spectrum of a particular element is unique
energy is absorbed which causes electrons to move up energy levels. Energy levels are different in each element. E=hf
Describe the main stages of a time of flight mass spectrometer and explain why it is able to separate isotopes
The sample is ionised then all the ions are accelerated to the same kinetic energy where they then move to the drift region where heavier isotopes move more slowly
State in terms of Avagardo’s constant, what is meant by a ‘mole’.
One mole contains Avogadro’s number (6.02X10’‘23) amount of particles
The mole ratio of Carbon atoms to Sulphur atoms in gunpowder is about 4:1
Explain why the mole ratio is greater than the mass ratio.
Ar of Carbon atoms is less than Sulphur atoms
Therefore more atoms of Carbon in a given mass or amount (e.g. per mole)
Other than electrical conductivity, what differences in physical properties are there between Carbon’s giant covalent structure and Sulphur’s simple covalent stucture.
Melting point is higher in carbon
What is the bond angle in a Sulpur-8 molecule and why?
109 degrees
4 areas of electron density around the central Sulphur atom
Electron pairs repel
To get as far away as possible
Give 3 features of gamma radiation
highly penetrating, its an electromagnetic wave, unaffected by electromagnetic fields
Use electron pair repulsion to principle to predict and explain the shape of SF6 and the bond angle S-F
90 degrees
Octahedral
there are 6 areas of electron density around a central S atom that repel as far apart as possible.
Why is empirical formula of a compound not always the same as the molecular formula
empirical formula is the the lowest ratio of atoms
Define isotope
Same element different mass due to number or neutrons
Explain why the relative atomic mass of an element isn’t a whole number but mass numbers of atoms are always whole number
Mass number is protons plus neutrons whilst Ar is an average of different isotopes
What does an atomic absorption spectrum look like
Coloured rainbow background with black lines(1) ;
getting closer at higher frequency(1) ;
State in terms of avogardro constant, what is meant the by a mole
A number of particles/ ions/ atoms/ molecules in one mole of a substance
What property did Mendeleev order the elements
Atomic weight
What is needed for a reaction to be classed as endothermic
More energy needs to be taken in to break bonds than energy released when bonds are made
What is nuclear fusion
The combining of nuclei to form a heavier nucleus
Explain how the information given on a mass spectrum, can be used to calculate the relative atomic mass of an element.
Mass of each isotope multiplied by
abundance/peak height/frequency/amount/intensity/value
Then calculate the average
What can’t radioactive decay be used to age archeological artefacts
Age of material small compared to half life
