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Chemistry A level > Atomic structure > Flashcards

Atomic structure Flashcards

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1
Q

What did Democritus discover about atoms and when?

A

-They were indivisible particles in a spherical shape
-430 bce

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2
Q

What did John Dalton discover about atoms and when?

A

-All matter was composed of atoms (indivisible building blocks)
-Different elements had different sized atoms
1803

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3
Q

What did JJ Thompson discover about the atom and when?

A

-Atoms contained negatively charged particles (electrons)
-Ball of positive charge with electrons embedded inside
-Plum pudding model
1897

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4
Q

What experiment did Rutherford do relating to the atom?

A

-Gold foil experiment
-Fired positively charged alpha particles through foil

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5
Q

What were the results of Rutherford’s alpha scattering experiment?

A

-Most passed straight through the foil but some deflected back

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6
Q

Who’s model did Rutherford prove wrong and when?

A

JJ Thompson’s plum pudding model in 1911

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7
Q

What did Niels Bohr discover about the atom and when?

A

-Electrons orbited the nucleus at different fixed energy levels called shells
-They spiralled down into the nucleus causing it to collapse
1913

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8
Q

What is the refined Bohr model?

A

-Scientists discovered that not all electrons in the same shell had the same energy levels
-Added sub shells
-Explained why some elements are inert

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9
Q

What did Bohr believe about electron shells and elements reactivity?

A

-They can only hold a fixed number of electrons
-Reactivity is due to the elements electrons so if the shell is full the element is inert

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10
Q

What did James Chadwick discover and when?

A

The existence of neutrons in 1932

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11
Q

What is the relative mass of protons, neutrons and electrons?

A

proton-1
neutron- 1
electron-1/1840

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12
Q

What is the relative charge of protons, neutrons and electrons?

A

protons- +1
neutron- 0
electron- -1

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13
Q

Why is the reactivity of different isotopes of an element identical?

A

they have the same number of electrons

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14
Q

What is the share of percentages of isotopes of chlorine?

A

75% chlorine-35
25% chlorine- 37

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15
Q

How many protons and electrons do isotopes of carbon have?

A

6 protons and so 6 electrons

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16
Q

Define relative atomic mass:

A

the average mass of its atoms, compared to 1/12 the mass of a carbon -12 atom

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17
Q

What are the key steps in a time of flight mass spectrometer?

A
  • Ionisation
  • Acceleration
  • Ion Drift
  • Detection
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18
Q

What happens during ionisation?

A

-The sample is ionised to enter the mass spectrometer
-Ionisation- the atom loses an electron and forms a 1+ positive charge

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19
Q

What are the two methods of ionisation?

A
  • Electrospray ionisation
  • Electron impact ionisation
20
Q

What happens during electrospray ionisation?

A
  • Sample is dissolved in solvent
  • pushed through small nozzle at high pressure
  • A high voltage applied - gains H+ ions and increases mass by 1
  • Solvent is removed - leaves gas made of positive ions
21
Q

What happens during electron impact ionisation?

A
  • Sample is vaporized
  • Electron gun used to fire HIGH ENERGY electrons at it
  • this knocks off one electron off one each particle - becomes +1 ions
22
Q

What happens during acceleration?

A
  • Positive ions are reflected by an electric field.
  • Electric field gives the same kinetic energy to all ions.
  • The lighter ions experience a greater acceleration
23
Q

What happens during ion drift?

A
  • The ions enter a region with no electric field
  • They drift through it at the same speed as they left the electric field.
  • Lighter ions will be drifting at high speeds
24
Q

What happens during detection?

A
  • Lighter ions reach the detector faster
  • Data from detector (current and time of flight) is used to calculate mass/charge values needed to produce a mass spectrum
25
Q

What does the detector measure?

A

The current created by ions and their time of flight.

26
Q

What does the y-axis represent in a mass spectrum?

A

The abundance of ions as a percentage.

27
Q

What does the height of each peak represent in a mass spectrum?

A

The relative isotopic abundance.

28
Q

What does the x-axis represent in a mass spectrum?

A

The mass/charge (m/z) ratio

29
Q

What is the relative isotopic abundance?

A

The amount of each isotope present in the sample

30
Q

How is the mass/charge ratio of each peak related to the isotope’s mass?

A

The mass/charge ratio is equal to the relative mass of the isotope since each ion is +1 charged

31
Q

What charge do ions have in a mass spectrometer?

A

Positive - mass spectrometer removes electrons

32
Q

What unit is mass/charge often shown in?

A

M/z

33
Q

What is first ionization energy?

A

Energy needed to remove one electron from each atom of an element in 1 mole of gaseous atoms, to form 1 mole of gaseous ions with a +1 charge

34
Q

What are the factors affecting ionization energy?

A
  • Nuclear charge : More protons = higher attraction
  • Distance from Nucleus : Further electrons are easier to move
  • Shielding : More inner electrons reduce the attraction to outer electrons
35
Q

Why does each successive electron require more energy?

A

So they can be removed due to increased nuclear charge and reduce shielding

36
Q

What is the general trend of 1st ionisation energy going down a group?

A

Decreases as you go down a group

37
Q

Why does 1st ionisation energy decrease as you go down the group?

A
  • atomic radius increases
  • distance between the nucleus and outer electron increases
  • shielding increases

THEREFORE the attraction between the nucleus and outer electron decreases, less energy required to remove the outer electron

38
Q

What is the general trend of 1st ionisation energy across a period?

A

Increases across a period

39
Q

Why does 1st ionisation energy increase as you go across a period?

A
  • nuclear charge increases
    -same shielding/ same distance of outer electron to nucleus

THEREFORE attraction between outer electron and nucleus increases, more energy needed to remove the outer electron

40
Q

When going across a period, why is there an exception for the trend between groups 2 and 3?

A

Be/B and Mg/Al

it is easier to remove due to shielding by full ‘s’ orbital (higher energy levels)

41
Q

When going across a period, why is there an exception for the trend between groups 5 and 6?

A

N/O and P/S

it is easier to remove due to electron pair repulsion

42
Q

What is successive ionisation energies?

A

the energy required to remove electrons one by one from the same atoms

43
Q

What are the equations for 2nd and 3rd ionisation energies?

A
44
Q

Why is there a general increase in ionisation energy (successive ionisation energies)?

A

Due to increasing effective charge on the nucleus

45
Q

Why are there large ‘jumps’ on the successive ionisation energies graphs?

A

Caused by electrons being taken from an energy level that is closer to the nucleus ie. decreased distance + decreased shielding THEREFORE stronger attraction

Chemistry A level (3 decks)

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