atomic structure

Question 1

what is the order of atomic discoveries?

Answer 1

Dalton, Thomson, Rutherford, Bohr , current model

Question 2

what did Dalton propose an atom was?

Answer 2

Dalton proposed that all atoms of one element are the same and are different from the atoms of another element. Atoms in his model were tiny and indivisible.

Question 3

what did Thomson propose the atom was?

Answer 3

the plum pudding model- He proposed the plum pudding model where negatively charged electrons move in a ‘sea’ of charge in a positively charged atom.

Question 4

What did Rutherford propose the atom was like?

Answer 4

​​1911- Rutherford found that most of the mass is concentrated in the small, dense positive nucleus, with negative electrons orbiting it in shells. The positive and negative charges balance to make the atom neutral.

Question 5

what did Bohr suggest the atom was like?

Answer 5

​​Bohr suggested that electrons orbit the nucleus on paths. Bohr’s planetary model provided an explanation for the difference in energy of electrons at different distances from the nucleus.

Question 6

how do you calculate the maximum number of electrons that an atom’s shell can hold?

Answer 6

​​the maximum number of electrons that an atom can hold can be calculated by using 2n^2
n= no. shells

Question 7

what is the mass number

Answer 7

can be written as A and is the sum of the no. protons and the no. neutrons in an atom

Question 8

what is atomic number?

Answer 8

the no protons in an atom

Question 9

define relative atomic mass

Answer 9

it is the weighted average mass of an atom of an element, taking into account its naturally-occurring isotopes, relative to 1/12th the relative atomic mass of an atom of Carbon-12

Question 10

define what is meant by an isotope

Answer 10

Isotopes are atoms with the same number of protons and different numbers of neutrons. Therefore, they have different mass numbers but the same atomic number.

Question 11

why do isotopes of the same element react chemically in the same way?

Answer 11

they have the same electronic configuration and atomic numbers so will react chemically in the same way but due to their different mass numbers, they have different physical properties

Question 12

what is mass spectrometry?

Answer 12

this is an analytical technique used to find out different isotopes and find the overall relative atomic mass of an element

Question 13

what is time of flight mass spectrometry?

Answer 13

this form of mass spectrometry records the time taken for ions of each isotope to reach a detector. using this, spectra can be produced, showing each isotope present.

Question 14

what is the process for TOF mass spectrometry?

Answer 14

1) ionisation
a sample of an element is vapourised and injected into the mass spectrometer where a high voltage is passed over the chamber. this causes electrons to be removed from the atoms- 1+ ions formed and left in the chamber
2) acceleration
positively charged ions are accelerated towards a negatively-charged detection plate
3) ion drift
the ions are then deflected by a magnetic field into a curved path. the radius of their path is dependent on the charge and mass of the ion
4) detection
when the positive ions hit the detection plate they gain an electron, producing a flow of charge. the greater the abundance, the greater the current produced
5)analysis
these current values are then used in combination w the flight time to produce a spectra print-out w the relative abundance of each isotope displayed

Question 15

what are the two methods of carrying out ionisation?

Answer 15

1) electron impact
2) electrospray ionisation

Question 16

what happens in electron impact?

Answer 16

it is used for elements with low Mrcompounds
- high energy electrons are fired at the sample from an electron gun
-this knocks off one electron from each atom/molecule to form 1+ ion:
X(g)->X^+(g) +e^-

Question 17

what happens in electrospray ionisation?

Answer 17

used for high Mr compunds eg. proteins
-sample dissolved in a volatile solvent eg. methanol and injected thru a fine hypodermic needle as a fine spray into a vacuum in the ionisation chamber
-a very high voltage is applied to the end of the needle where the spray emerges (the needle is positively charged)
-the particles gain a proton and become ions as a fine mist : X(g)+ H^+ -> XH^+(g)
-the solvent evaporates leaving 1+ ions

Question 18

why are the ions accelerated?

Answer 18

the ions are accelerated using an electric field so that all the ions have the same kinetic energy

Question 19

when does separation of ions occur?

Answer 19

in the flight tube during ion drift
ions w different masses have a different time pf flight
-the lighter ions travel faster and take less time to reach the detector

Question 20

what is indicated on the spectra by half of the mass to charge ratio (m/z)?

Answer 20

during ionisation, a 2+ ion can be produced = affected more by the magnetic field= curved path of a smaller radius
= m/z halved and can be seen on the spectra as a trace at half the expected m/z value