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A-Level Chemistry > Atomic Structure > Flashcards

Atomic Structure Flashcards

1
Q

What is Relative Atomic Mass? (Ar)

A

Ar is the average mass of an atom of an element on a scale where an atom of carbon-12 is exactly 12

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2
Q

What is Relative Isotopic Mass?

A

This is the mass of an atom of an isotope of an element on a scale where an atom of carbon-12 is exactly 12

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3
Q

What is Relative Formula Mass?, How do you find it? and What is it used for?

A

This is the average mass of a formula unit on a scale where an atom of carbon-12 is exactly 12 (add up all Ar of ions in the formula), this is used for ionic compunds

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4
Q

What is Relative Molecular Mass? (Mr) and How do you find it?

A

Mr is the average mass of a molecule on a scale where an atom of carbon-12 is exactly 12
Mr = (isotopic mass x percentages)/total percentages

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5
Q

Describe the Dalton atomic model

A
  • Solid sphere
  • Each element made up of one type of atom only
  • Learn diagram
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6
Q

Describe the JJ Thompson atomic model

A
  • Plum Pudding model
  • discovered the electron (negative and small)
  • Negative electrons (plums) and positive pudding
  • Learn diagram
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7
Q

Describe the Rutherford atomic model

A
  • Discovered the nucleus (tiny, massive and positive)
  • Gold Foil experiment
  • Most of the atom is empty space
  • Alpha particles shot in and most get through but some are deflected (by nucleus)
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8
Q

Describe the Bohr atomic model

A
  • Put electrons in shells
    MASS CHARGE
    P 1 +1
    E 1/2000 -1
    N 1 0
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9
Q

How are ions formed and what are they?

A

Formed by gaining or losing electron and they are atoms with different numbers if protons and electrons

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10
Q

How do you work out the number of neutrons?

A

neutrons is mass number minus atomic number

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11
Q

Why are atoms neutral?

A

They have the same number of protons as electrons

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12
Q

What is an isotope?

A

An isotope of an element are atoms with the same number of protons but different numbers of neutrons

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13
Q

What decides the chemical properties an element?

A

Number and arrangement of electrons

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14
Q

Why do isotopes have the same chemical properties but slightly different physical properties?

A
  • Same chemical properties because they have the same configuration of electrons
  • They have slightly different physical properties because they depend on the mass of the atom
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15
Q

What is the atomic number?

A

It is the number of protons and it identifies the element

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16
Q

What is the mass number?

A

It is the total number of protons and neutrons in the nucleus

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17
Q

What are the symbols for mass number and atomic number?

A

Atomic number = Z

Mass number = A

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18
Q

Describe group 0 elements

A

They have completely filled S and P sub shells (don’t gain, lose or share electrons). This makes them inert

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19
Q

Describe S block elements (Group 1 and 2)

A

They have 1 or 2 outer electrons, they are easily lost to form positive ions with an inert gas configuration

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20
Q

Describe P block elements (Group 5, 6 and 7)

A

They gain 1, 2 or 3 electrons to form negative ions with an inert gas configuration

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21
Q

What can Group 4-7 elements form?

A

Covalent bond because they can share electrons

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22
Q

What do electrons have in relation to electron shells?

A

They have fixed energies and they move around the nucleus in shells or energy levels

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23
Q

What are each shell given? and When is this higher?

A

a principal quantum number (further from nucleus mean higher principal quantum number and higher energy)

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24
Q

What do all electrons in the same shell have?

A

The same energy

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25
Q

What are the 4 types of sub shells?

A

S, P, D and F

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26
Q

What are shells divided into?

A

Sub-shells

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27
Q

What do different shells have?

A

different numbers of subshells which each have different energy

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28
Q

What do each type of sub shells have?

A

different numbers of orbital

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29
Q

How many electrons can an orbital hold and how many orbitals does each type of sub shell have?

A
  • Orbitals can hold 2 electrons
  • S sub shells have 1 orbital so hold 2 electrons
  • P sub shells have 3 orbitals so hold 6 electrons
  • D sub shells have 5 orbitals so hold 10 electrons
  • F sub shells have 7 orbitals so hold 14 electrons
30
Q

What is sub shell notation and describe the different parts of it?

A

EG. 1s2 2s2 2p6

31
Q

Learn arrow in boxes diagrams and why are the arrows in the boxes in opposite directions

A

The boxes represent orbitals and the arrows are opposite because the electrons are spinning in opposite directions

32
Q

Learn energy level digrams, What do they show?

A

they show energy of electrons in different orbitals, as well as the number of electrons and the arrangement

33
Q

What are the rules for sub shells?

A
  • Electrons fill the lowest energy sub shells (4s before 3d)
  • Electrons fill orbitals in a sub shells singly before they share an orbital
  • With ions, highest energy levels leave first but 4s leaves before 3d
34
Q

What are the two exception for these rules and why are they like this?

A
  • Chromium - 1s2 2s2 2p6 3s2 3p6 4s1 3d5
  • Copper - 1s2 2s2 2p6 3s2 3p6 4s1 3d10]
  • They both only have one electron in the 4s sub shell because it makes them more stable
35
Q

What is the first ionisation energy? and Write an example equation

A

This is the energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions
Eg. O(g) –> O+(g) + e-

36
Q

What are some important points in relation to ionisation energies?

A
  • Refer to 1 mole of atoms rather than to a single atom
  • Lower ionisation energy means its easier to form +ions
  • Use state symbols because ionisation energies are measure for gaseous atoms
37
Q

What are the factors that affect ionisation energy?

A
  • Nuclear Charge (more protons = more positive charge so electron attraction is stronger)
  • Distance from nucleus (attraction falls with distance because electrons have less attraction)
  • Shielding (as the number of e- between outer shell and nucleus increase, outer electron has less attraction. This is due to the number of inner shells)
38
Q

What is the second ionisation energy? and Write an example equation

A

This is the energy needed to remove an electron from each ion in 1 mole of gaseous 1+ ions
Eg O+(g) –> O2+(g) + e-

39
Q

Why is second ionisation energy greater than the first?

A
  • Removing electron from an ion (stronger attraction)

- Electron configuration has changed

40
Q

What is a successive ionisation energy?

A

You can remove all electrons so there is just a nucleus, each time there is a successive ionisation energy

41
Q

What is the equation for successive ionisation energies?

A

X(n-1)+(g) –> Xn+(g) + e-

42
Q

What is the trend of ionisation energies down a group?

A

Distance from nucleus and shielding increase so it is easier to remove electron, even though nuclear charge increases

43
Q

What is the general trend of ionisation energies across a period?

A

Left to right ionisation energies increase because distance of electrons from nucleus is similar and shielding is the same but nuclear charge increases

44
Q

Why are the two dips across a period due to?

A
  • sub shell dip

- Electron pair repulsion dip

45
Q

What is the sub shell dip between Mg and Al due to?

A

Even though charge increases, Al’s ionisation energies is lower because Al has more shielding and its outer electron is further from nucleus than Mg’s

46
Q

What is the electron pair repulsion dip between P and S due to?

A

The outer electron for S is easier to remove than P’s because the outer electron from S comes from an orbital with 2 electrons (which repel each other), meaning less energy is needed for the first ionisation energy of S. Even though distance is the same and nuclear charge increases

47
Q

Learn the diagrams for the increase ionisation energy throughout electrons in different shells

A

Describe what they mean

48
Q

Why are there big jumps in ionisation energies between shells?

A

This is because electrons are closer to the nucleus

49
Q

Why are there successive ionistion energies within each shell?

A

this is because they are removed from an increasingly positive ion, because there is less repulsion amongst electrons (stronger)

50
Q

Describe the method for electron impact ionisation (give the equation)

A
  • Sample is vaporized
  • High energy electron is fired at the sample
  • Knocking one electron from each particle forming 1+ ions (called the molecular ion)
  • X(g) + e- –> X+(g) + 2e-
51
Q

What does the molecular ion do when it is detected?

A

breaks into small fragments that are detected

52
Q

What is an electron gun?

A

Hot wire filament with a current

53
Q

What sort of elements is electron gun ionisation used for?

A

elements with low formula mass

54
Q

Describe the method for electrospray ionisation (give the equation)

A
  • Sample is dissolved in a volatile solvent
  • Then injected through a fine hypodermic needle to give a fine mist
  • Tip of the needle is attached to a positive terminal (high voltage)
  • particles ionised by giving a H+ ion from the solvent as they leave the needle forming XH+ ions
  • X(g) + H+ –> XH+(g)
55
Q

What elements is electrospray ionisation used for?

A

elements with higher molecular mass (proteins)

56
Q

What is electrospray ionisation also called and what rareley happens?

A

Known as ‘soft’ ionisation and fragmentation rarely occurs

57
Q

Describe acceleration in a mass spectrometer

A
  • positive ions are accelerated using an electric field

- so all the ions have the same kinetic energy

58
Q

What does velocity of the ions depend on?

A
  • Mass of each particle (lighter = faster)
59
Q

Learn the equations for acceleration and what are the units for each part?

A 
KE = 1/2MV²
V = square root of (2KE/M)
KE = J
M = mass in kg
V = velocity in m/s
60
Q

What does time of flight depend on?

A

Depends on velocity and so mass

61
Q

What do the + ions travel through?

A

Travel through the hole in the negative plate and into the tube

62
Q

What is time of flight proportional to?

A
  • the square root of the mass of an ion

- Lighter = fast = reach detector quicker

63
Q

What does d stand for?

A

length of tube

64
Q

What are the equations for time in a mass spectrometer?

A
  • T = d/v

- T= d x square root of (M/2KE)

65
Q

Describe how ions are detected

A
  • positive ion hits negative detector and are discharged by gaining an electron
  • Generates a movement of electrons and a current is measured
  • Size of current gives a measure of the number of ions hitting the plate
66
Q

How do you work out Ar?

A

Ar = (mass of all isotopes x abundance of each isotope)/ abundance of all isotopes

67
Q

How is the mass spectrum produced? And what does the mass spectrum show?

A
  • computer uses data to produce mass spectrum

- Shows mass to charge (m/z) ratio and abundance of each ion that gets to the detector

68
Q

What is M/Z in electrospray ionisation?

A

It is effectively mass

69
Q

What is the signal greatest with the greatest M/Z value from? And what does this value give? (electron impact)

A

The molecular ion and it gives the relative molecular mass

70
Q

Why would there be other peaks around the molecular peak? (electron impact)

A

This is due to different isotopes

71
Q

Why would there be peaks at lower M/Z values? (electron impact)

A

This is due to fragments

A-Level Chemistry (8 decks)

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