Elements of Life

Question 1

Explain what is meant by half life

Answer 1

time taken for half a radioactive isotope to decay

Question 2

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.

Answer 2

short - would not be around in sufficient levels to detect.

long - possible to harm the patient

Question 3

Why did Mendelev leave gaps in the periodic table

Answer 3

For elements to be discovered

Question 4

How did later evidence from the scientific community support Mendeleev’s decision to leave gaps in his Periodic Table?

Answer 4

New elements were found that showed properties that fitted in with the groups

Question 5

Which group in the modern Periodic Table is missing from Mendeleev’s table?

Answer 5

Group 8/0

Question 6

How do you measure the volume of gas

Answer 6

find out how many moles of the substance there is and times it 24000

Question 7

What is entropy

Answer 7

The measure of disorder

Question 8

A fossil has a count rate of 12.5%. How many half lifes has it had

Answer 8

3

Question 9

Name 2 assumptions that have to be made when calculating half life by count rate

Answer 9

half life unaffected by temperature or pressure

No loss or gain of radioisotope

Question 10

Name two observations when calcium reacts with water

Answer 10

Gas is given off and the calcium dissolves

Question 11

What information is given by the height of the peak in mass spec

Answer 11

The relative abundance

Question 12

State the radioactive decay that turns hydrogen-3 into helium-3. Explain your answer

Answer 12

beta decay, where one neutron is converted into a proton

Question 13

Suggest why high temperature and pressure are need for nuclear fusion

Answer 13

Needs to overcome the repulsion of the two positively charged nuclei

Question 14

Describe the appearance of an atomic absorption spectrum

Answer 14

Black lines of a coloured background

Question 15

Describe the appearance of an atomic emission spectrum

Answer 15

Coloured lines on a black backgrouns

Question 16

Explain in terms of electronic levels, why the absorption spectrum of a particular element is unique

Answer 16

energy is absorbed which causes electrons to move up energy levels. Energy levels are different in each element. E=hf

Question 17

Describe the main stages of a time of flight mass spectrometer and explain why it is able to separate isotopes

Answer 17

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

Question 18

State in terms of Avagardo’s constant, what is meant by a ‘mole’.

Answer 18

One mole contains Avogadro’s number (6.02X10’‘23) amount of particles

Question 19

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.

Answer 19

Ar of Carbon atoms is less than Sulphur atoms

Therefore more atoms of Carbon in a given mass or amount (e.g. per mole)

Question 20

Other than electrical conductivity, what differences in physical properties are there between Carbon’s giant covalent structure and Sulphur’s simple covalent stucture.

Answer 20

Melting point is higher in carbon

Question 21

What is the bond angle in a Sulpur-8 molecule and why?

Answer 21

109 degrees
4 areas of electron density around the central Sulphur atom
Electron pairs repel
To get as far away as possible

Question 22

Give 3 features of gamma radiation

Answer 22

highly penetrating, its an electromagnetic wave, unaffected by electromagnetic fields

Question 23

Use electron pair repulsion to principle to predict and explain the shape of SF6 and the bond angle S-F

Answer 23

90 degrees
Octahedral
there are 6 areas of electron density around a central S atom that repel as far apart as possible.

Question 24

Why is empirical formula of a compound not always the same as the molecular formula

Answer 24

empirical formula is the the lowest ratio of atoms

Question 25

Define isotope

Answer 25

Same element different mass due to number or neutrons

Question 26

Explain why the relative atomic mass of an element isn’t a whole number but mass numbers of atoms are always whole number

Answer 26

Mass number is protons plus neutrons whilst Ar is an average of different isotopes

Question 27

What does an atomic absorption spectrum look like

Answer 27

Coloured rainbow background with black lines(1) ;
getting closer at higher frequency(1) ;

Question 28

State in terms of avogardro constant, what is meant the by a mole

Answer 28

A number of particles/ ions/ atoms/ molecules in one mole of a substance

Question 29

What property did Mendeleev order the elements

Answer 29

Atomic weight

Question 30

What is needed for a reaction to be classed as endothermic

Answer 30

More energy needs to be taken in to break bonds than energy released when bonds are made

Question 31

What is nuclear fusion

Answer 31

The combining of nuclei to form a heavier nucleus

Question 32

Explain how the information given on a mass spectrum, can be used to calculate the relative atomic mass of an element.

Answer 32

Mass of each isotope multiplied by
abundance/peak height/frequency/amount/intensity/value
Then calculate the average

Question 33

What can’t radioactive decay be used to age archeological artefacts

Answer 33

Age of material small compared to half life