atomic structure

Question 1

Relative atomic mass

Answer 1

The average mass of an atom of an element compared to 1/12th the mass of an atom of carbon-12.

Question 2

Relative isotopic mass

Answer 2

The mass of an atom of an isotope of an element compared to 1/12th the mass of an atom of carbon-12.

Question 3

Relative molecular mass

Answer 3

The average mass of a molecule compared to 1/12th the mass of an atom of carbon-12

Question 4

Mass number

Answer 4

The sum of neutrons and protons in an atom.

Question 5

Atomic number

Answer 5

The number of protons in an atom.

Question 6

history of atomic theory

Answer 6

dalton-stated that atoms are the smallest forms of matter
thompson- discovered electrons and proposed the plum pudding model which stated that atoms were a sphere of positive charge with electrons evenly distributed within it.
rutherford, geiger and marsden- conducted the alpha scattering experiment by firing alpha particles at a thin gold foil. mostly empty space as most particles went straight through, positive charge in the middle as some were deflected, small, dense nucleus as some bounced straight back.
bohr- proposed that electrons orbit the nucleus in shells.
chadwick-discovered neutrons

Question 7

what is mass spectrometry

Answer 7

the mass spectrometer gives accurate information about relative isotopic mass and also about the relative abundance of isotopes.

Question 8

what can mass spectrometry be used for

Answer 8

to collect data on the mass and abundance of elements

Question 9

electron impact ionisation

Answer 9

-sample is vapourised, high energy electrons are fired at it
-the electrons are emitted from a charged hot wire filament
-the electrons knock off one electron from each particle, forming 1+ ions.
X(g) + e^- —> X^+(g) + 2e^-
-used for substances with low RFM
-the ions often fragments which may also be detected

Question 10

electrospray ionisation

Answer 10

-the sample is dissolved in a volatile solvent and injected through a fine, positively charged hypodermic needle so it become a fine mist.
-the particles are ionised by gaining a proton from the solvent as they leave the needle, producing XH+ ions
X(g) + H^+ —> XH^+(g)
-the solvent evaporates away
-it is used for substances with higher RFM such as proteins
-fragmentation is rare

Question 11

acceleration

Answer 11

• the positive ions are accelerated so that they all have the same kinetic energyusing an electric field towards a negatively charged detection plate.
• as the kinetic energy is the same, the velocity depends on the mass of the ions

Question 12

drift

Answer 12

• the positive ions travel through a hole in the negatively charged plate into a flight tube
• the TOF depends on its velocity

Question 13

detection

Answer 13

-Once they have pass through the mass spectrometer, the 1+ ions will hit a negatively charged ‘detector’ plate
-As they hit this electric plate, they gain an electron
which causes a current to be produced
-This size of the current is proportional to the abundance of the ions hitting the plate and gaining an electron
-The detector plate is connected to a computer, which produces the mass spectra.
- a spectrum shows the mass to charge ratio (m/z) and the abundance of each ion that reaches the detector.

Question 14

why might there be a trace at half the expected m/z value

Answer 14

during the ionisation process, a 2+ ion may be produced so the m/z ratio is halved

Question 15

define first ionisation energy

Answer 15

the energy required to remove 1 mole of electrons from 1 mole of gaseous atoms.

Question 16

formulas for 1st 2nd and 3rd ionisation energy

Answer 16

1st:
X(g) --> X^+(g) +e^-
2nd:
X^+(g) --> X^2(g)+e^-
3rd:
X^2+(g) --> X^3+(g) + e^-

Question 17

factors affecting ionisation energy

Answer 17

proton number- more protons=stronger attraction between the nucleus and the outer e^-s.
atomic radius - smaller radius = outer e^-s are closer to nucleus so stronger attraction.
shielding - more inner electrons weakens the attraction between the nucleus and outer e^-s.

Question 18

why is IE always positive

Answer 18

-energy is always needed to remove an e^- from an atom as it is attracted to the positive nucleus.

Question 19

why is 2nd ionisation energy always bigger

Answer 19

the atoms becomes a positive ion so there is a stronger attraction between outer electrons and positive nucleus

Question 20

why can there be a big jump in IE

Answer 20

the next electron being removed is in the next shell which is closer to the nucleus.

Question 21

what are the periodic trends

Answer 21

atomic radii decreases as you go across a period. this is because the number of protons increases so the nuclear charge also increases. therefore, there is a stronger pull on the e- shells. ionisation energy increases across a period due to more protons but same shielding so stronger attraction between nucleus and outer e-s.

Question 22

what are the different subshells, how many orbitals do they have and how many e-s can they hold

Answer 22

S sub-shell has 1 orbital which holds 2 e-s
P subshell has 3 orbitals which holds 6 e-s
D subshell has 5 orbitals which holds 10 e-s
F subshell has 7 orbitals which holds 14 e-s

Question 23

why does the 4s subshell come before the 3d subshell

Answer 23

it has lower energy so fills first

Question 24

exceptions to the electronic configuration order

Answer 24

copper: 1s^2, 2s^2, 2p^6, 3s^2, 3p^6, 4s^1, 3d^10
chromium: 1s^2, 2s^2, 2p^6, 3s^2, 3p^6, 4s^1, 3d^5

Question 25

explain the group 2 to 3 dip in ionisation energy

Answer 25

the outer electron is being lost from the 3p subshell rather than 3s in magnesium. it is a higher energy shell so the e- is removed easier

Question 26

explain the 5 to 6 dip in ionisation energy

Answer 26

sulphur has paired electrons in the 3p subshell whereas phosphorous doesn’t. this causes electron-electron repulsion which decreases ionisation energy

Question 27

how does melting point change across a period

Answer 27

increases until group 4 and then decreases. metals on the left then covalent