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atomic structure Flashcards

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1
Q

what are the isotopes?

A

atoms of the same element with the same number of protons but a different number of neutrons

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2
Q

why do different isotopes react exactly the same way chemically?

A

their electron configuration is exactly the same

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3
Q

why can mass numbers include decimals?

A

it takes into account the average isotope abundance

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4
Q

what is the mass number for isotopes equation?

A

(mass of isotope x%) + (mass of isotope x %) / 100

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5
Q

which isotopes are radioactive and are found in tiny amounts in all carbon based lifeforms?

A

14
C
6

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6
Q

on a
14
C
6
isotope, how can radiation be measured?

A

the unstable nucleus decays very consistently and gives off radiation that can be measured

the measurable radiation exactly halves every 5730 years- called halflife

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7
Q

how long is the half life for
14
C
6 isotopes?

A

5730 years

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8
Q

what do mass spectra enable you to do?

A

to find relative abundances of the isotopes of a particular element

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9
Q

what does relative atomic mass mean?

A

the mass number is the average mass of the isotopes for an element on a scale on which a carbon 12 atom has a mass of exactly 12 units

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10
Q

what is the equation for relative atomic mass?

A

average mass of 1 atom // 1/12 mass of 1 atom of C12

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11
Q

what is the equation for relative molecular mass?

A

average mass of molecule // 1/12 mass of 1 atom of C12

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12
Q

what are the four uses of mass spectrometry?

A
  1. identifying unknown atoms or compounds by working out Ar or Mr
  2. gain further information about isotopes- determining abundance of each isotope in an element
  3. detecting banned substances such as steroids in athletes urine
  4. repired gas samples from patients under anaesthetic
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13
Q

what is a TOF?

A

time of flight spectrometer

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14
Q

what are the two methods of ionisation of a sample that we should know about?

A

electron impact and electrospray ionisation

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15
Q

in the electron impact method, what is the role of the electrons?

A

electrons are fired at the vaporised sample using an electron gun

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16
Q

what happens when the electrons hit the sample?

A

other electrons are knocked off same atoms, leaving the sample positively charged

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17
Q

what happens to the now positive ions in the time of flight spectrometer ?

A

positive ions are then accelerated by being repelled by the positive plate on the left and attracted to the negative plate on the right.

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18
Q

write an equation, including state symbols, to show how an atom is ionised by electron impact?

A

Sample X(g) + e- —–> Sample X+(g) + 2e-

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19
Q

in electrospray ionisation, what happens to the sample?

A

it is dissolved in a volatile solvent (e.g. water) and sprayed through a very fine positively charged needle. this is a high voltage charge

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20
Q

what does the solvent act as in electrospray ionisation?

A

a source of protons (H+) to allow the ionisation process.

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21
Q

what is similar about the electron gun and electrospray ionisation method?

A

sample is left positively charged

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22
Q

how are we left with the SampleH+ ion in electrospray ionisation?

A

the solvent is evaporated, leaving the sample H+ ion which is accelerated towards the negatively charged plate

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23
Q

write an equation, including state symbols to show the ionisation of a sample through electrospray ionisation?

A

Sample (g) + H+ ——–> SampleH+(g)

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24
Q

why is the whole TOF process done in a vacuum?

A

prevents fast moving ions colliding with gas molecules in the air

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25
Q

how can we accelerate positive ions in the TOF spectromoeter?

A

positive ions are attracted to the negatively charged plate using an electric field so that they all have the same kinetic energy

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26
Q

why do all ions not accelerate at the same speed?

A

heavier ions and less positively charged ions accelerate to lesser speeds and take longer to reach the detector at the end of the flight tube- their TOF is greater

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27
Q

what happens to the ion in a TOF spectrometer once it hits the detector?

A

it gains an electron to become neutral and cause a current to flow shich can be detected- this current is proportional to the abundance

flight time is recorded

28
Q

what can the mass spectrometer do for each isotope?

A

measure a m/z (mass/charge ratio) and an abundance

29
Q

what is an example of how mass spectrometers have been used in real life?

A

they have been included in planetary space probes so that elements on other planets can be identified- elements on other planets can have a different composition of isotopes.

30
Q

what does m/ z mean for mass spectrometry?

A

mass to charge ratio

31
Q

if two electrons are removed in mass spectrometry, forming a 2+ ion, what happens to the m/z value?

A

it halves, e.g. 24Mg2+ will have a m/z of 12

32
Q

what does the peak with the largest m/z on the mass spectrum represent?

A

it will be due to the complete molecule and will be equal to the Mr of the molecule

this peak is called the parent ion or the molecular ion

33
Q

when does fragmentation occur in mass spectrometry? when does it not occur?

A

if a molecule is put through a mass spectrometer with an electron impact ionisation stage then it will often break up and give a series of peaks caused by the fragments

it won’t occur in electrospray ionisation

34
Q

in electrospray ionisation, how will peaks be shown on the mass spectrum?

A

there will be one peak equal to the mass of the MH+ ion- we therefore have to subtract 1 to get the Mr of the molecule

35
Q

what are the basic energy levels called in chemistry?

A

principle energy levels numbered 1,2,3,4…
1 is closest to the nucleus

36
Q

what is contained within each principle energy level ?

A

sub-levels
level 1 holds 1s
level 2 holds 2s,2p
level 3 holds 3s,3p,3d
level 4 holds 4s,4p,4d,4f

37
Q

how many electrons can each sub level hold?

A

s holds up to 2 electrons
p holds up to 6 electrons
d holds up to 10 electrons
f holds up to 14 electrons

38
Q

what is an important thing to note about filling sub shells?

A

3d is in a higher energy level than 4s so gets filled after 4s

39
Q

what are sub energy levels further split into?

A

orbitals which hold up to 2 electrons of opposite spin

40
Q

what are the shapes of the s and p orbitals?

A

s- sphere
p- dumbbell

41
Q

what is the rule for filling up sub levels with several orbitals?

A

fill each orbital singly before starting to pair up electrons

42
Q

what do the arrows pointing in opposite directions in spin diagrams represent?

A

the different spins of the electrons in the orbital?

43
Q

what are the exceptions for copper and chromium?

A

only half fill the 4s orbital because it is more thermodynamically stable to move one electron away from the 4s and to the 3d

44
Q

if you’re a transition metals, what happens when you form an ion?

A

you lose the 4s before the 3d

45
Q

what is the definition of the first ionisation energy?

A

the enthalpy change when one mole of gaseous atoms forms one mole of gaseous ions with a single positive charge

46
Q

what is a more simplified definition of ionisation energy?

A

the energy required to remove a mole of electrons from a mole of atoms in a gaseous state (in KJmol-1)

47
Q

how is the first ionisation energy represented in an equation?

A

H(g) ——-> H+(g) + e-

48
Q

what is the definition of the second ionisation energy?

A

the enthalpy change when one mole of gaseous ions with a single positive charge forms one mole of gaseous ions with a double positive charge

49
Q

what are the factors that affect the ionisation energy?

A
  1. attraction of the nucleus (the more protons the greater the attraction)
  2. the distance of the electrons from the nucleus (the bigger the atom the further the outer shell electrons are from the nucleus and weaker attraction to the nucleus)
  3. shielding of the attraction of the nucleus (an electron in an outer shell is repelled by electrons in complete inner shells, weakening the attraction to the nucleus)
50
Q

why are successive ionisation energies always larger?

A

the ion already formed increases the attraction on the remaining electrons and so the energy required to remove the next electron is larger

51
Q

why has helium got the largest first ionisation energy?

A

the first electron is in the first shell closest to the nucleus and has no shielding effects from the inner shells- bigger IE than Hydrogen as it has 1 more proton

52
Q

why do IE’s decrease down a group?

A

number of electrons shells increases so increased shielding so the nuclear attraction between nucleus and outer electrons is weaker so it is easier to remove an electron

53
Q

why is there a general increase in IE across a period?

A

Similar shielding but more protons (greater nuclear charge) so greater nuclear attraction between nucleus and outer electrons

so harder to remove an electron

54
Q

why does sodium have a much lower first ionisation energy than neon?

A

outer electron is in a 3s shell further from the nucleus and more shielded

55
Q

why is there a small drop in IE from Mg to Al?

A

in Al, outer electron is being removed from the 3p orbital instead of 3s

3p electron higher in energy and also slightly shielded by 3s electrons so requires less energy to remove

56
Q

why is there a small drop in IE from P to S?

A

with sulfur there are 4 electrons in the 3p sub shell and the 4th is starting to doubly fill the 3p orbital

when the second electron is added to a 3p orbital there is slight repulsion between the two negatively charged electrons which makes the second electron easier to remove

57
Q

what is the fundamental particle that would not be deflected by an electric field?

A

neutron

58
Q

what did dalton say the atom was?

A

proposed that elements were composed of invisible atoms that were all the same mass for certain elements

59
Q

what did thompson say the atom was (PP model)?

A

discovered negatively charged ‘electrons’ that were randomly located in positive spheres like plums in a pudding

60
Q

who carried out the gold experiment?

A

Rutherford

61
Q

what development did rutherford do?

A

used the gold experiment to discover the presence of a dense, positive charge nucleus containing protons with mass. Most of the atom was in fact empty space

62
Q

what did bohr do in the discovery of the atom?

A

worked out that electrons were in ‘energy levels’ around the nucleus

63
Q

what is the most recent addition to the description of the atom?

A

discovery of where the ‘missing mass’ was coming from. the neutral neutrons in the nucleus made up nearly half of the space in the atom

64
Q

what is the order of the discovery of the fundamental particles in the atom?

A

electron
proton
neutron

65
Q

what is the order of the models for the discovery of the atom?

A

1) solid sphere
2) plum pudding
3) nuclear
4) planetary (Bohr)
5) chadwick

Chemistry (4 decks)

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