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Chemistry > Atomic Structure > Flashcards

Atomic Structure Flashcards

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1
Q

What is the relative mass of an electron?

A

1/1840

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2
Q

What is the definition of atomic number?

A

The atomic number (i.e. proton number), Z, is equal to the number of protons.

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3
Q

What is the definition of mass number?

A

The mass number, A, is equal to the number of protons and neutrons combined.

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4
Q

What is a positive ion?

A

A cation is an atom that has lost electrons so that there are more protons than electrons.

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5
Q

What is a negative ion?

A

An anion is an atom that has gained electrons so that there are more electrons than protons.

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6
Q

What is the definition of an isotope?

A

Isotopes are atoms with the same number of protons but a different number of neutrons.

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7
Q

What is said about the chemical properties of isotopes?

A

Isotopes of the same element have the same chemical properties because they have the same electron configuration.

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8
Q

What is a mass spectrometer used for?

A

It is used to analyse elements or compounds and it can accurately determine the relative atomic mass (Ar) of atoms, or the relative molecular mass (Mr) of molecules.

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9
Q

What is the name of the mass spectrometer that we study at A Level?

A

Time of Flight (TOF) mass spectrometer

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10
Q

What is the first step inside the spectrometer?

A

Vacuum - the entire machine is a vacuum inside to prevent any of the particles being tested colliding with molecules from the air

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11
Q

What is the second step inside the spectrometer?

A

Ionisation

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12
Q

What are the two methods of ionisation of a sample?

A

electrospray ionisation and electron impact ionisation

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13
Q

Describe electrospray ionisation?

A
  • Substance dissolved in a volatile liquid
  • passed through a needle
  • a high voltage is applied to the sample
  • each atom gains a proton to form a positive ion
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14
Q

Describe electron impact ionisation

A
  • the sample is vapourised and high energy electrons are fired at it
  • this causes each atom to lose an electron, forming a positive ion
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15
Q

What is the third step inside the spectrometer?

A

Acceleration - the positive ions are attracted to a negatively charged plate and accelerate towards it

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16
Q

What does the ion’s acceleration depend on?

A

the amount they accelerate depends on the mass to charge (m/z) ratio of the ion - high m/z ratio ions will accelerate to lower speeds than low m/z ratio ions

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17
Q

What happens when all the ions have accelerated?

A

Once accelerated all ions will have the same kinetic energy

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18
Q

What is the fourth step inside the spectrometer?

A

Ion Drift - some of the ions will pass through a hole in the negatively charged plate. They form a beam of particles and travel along the ‘flight tube’ towards the detector. Because the particles are travelling at different speeds by this point, they start to drift apart further as the slower particles can’t keep up with the faster ones.

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19
Q

What is the fifth step inside the spectrometer?

A

Detection

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20
Q

Describe the detection step in the spectrometer

A
  • Each ion hits the detector and gains an electron
  • This induces an electric current, the size of which is proportional to the abundance
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21
Q

What happens when a single element is injected into a mass spectrometer?

A

the sample will be separated into the different isotopes of that element

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22
Q

On a mass spectrum, what does each peak on the graph represent?

A

a different isotope as each will have a different m/z ratio

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23
Q

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

A

the relative abundance of each isotope

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24
Q

What is the formula for calculating Ar?

A

Ar =[ (mass 1 x abundance 1) + (mass 2 x abundance 2) + (mass n x abundance n) ]/ the sum of abundances

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25
Q

Why may a large range of different peaks form?

A

some elements don’t always split into individual atoms e.g. chlorine usually exists as a diatomic molecule

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26
Q

What is the kinetic energy equation? and the SI units?

A

KE = 1/2 mv^2
KE in Joules (J)
Mass in kg
Velocity in m/s
Distance in m
Time in s

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27
Q

What is the equation for velocity?

A

d/t

28
Q

How do you calculate the mass of an ion in kg?

A

1, Divide the mass number of the ion by Avogadro’s constant
2, This has calculated the mass in g so now convert to kg by dividing by 1000

29
Q

What is Avogadro’s constant?

A

6.022 x 10 ^ 23

30
Q

The 1st energy level is where in relation to the nucleus?

A

closest to the nucleus

31
Q

How many electrons can be held in each of the first four energy levels?

A

1, two
2, eight
3, eighteen
4, thirty-two

32
Q

What is within each energy level?

A

sub-shells

33
Q

What is within each sub-shell?

A

orbitals

34
Q

What is an orbital?

A

An orbital is a region within an atom that can hold up to two electrons with opposite spins

35
Q

What is the s orbital shape?

A

spherical

36
Q

What is the p orbital shape?

A

a dumbbell shape

37
Q

Within the s sub-shell how many s orbitals are there?

A

one

38
Q

Within the p sub-shell how many p orbitals are there?

A

three

39
Q

Within the d sub-shell how many d orbitals are there?

A

five

40
Q

How many electrons can be held in one orbital?

A

two

41
Q

Which is the energy orbital with the lowest energy?

A

those closest to the nucleus

42
Q

What is the outer most electron on an atom or ion termed as?

A

the highest energy electron because it is the furthest from the nucleus

43
Q

On energy level diagrams, what do the arrows represent?

A

electrons which spin in different directions

44
Q

When electrons surround a nucleus there are three rules for how to allocate electrons to orbitals. What are they?

A

1, Orbitals of lower energy are always filled first.
2, Atomic orbitals of the same energy fill singly before electrons pair up.
3, No orbital can have more than two electrons.

45
Q

In an electron configuration, what do the large numbers refer to?

A

the shell or energy level of the electron

46
Q

In electron configuration, what do the letters refer to?

A

the sub shell of the electron

47
Q

In electron configuration, what do the small numbers refer to?

A

the number of electrons in that sub shell

48
Q

Which sub level electrons have lower energy 4s or 3d?

A

4s and so electrons would fill that sub level first

49
Q

How many exceptions are there when dealing with d-block elements and their electron configuration?

A

three

50
Q

What are the first two exceptions to the normal rule of electron configuration for d-block elements due to?

A

‘d-block elements are more stable when they have a full, or exactly half full d sub shell’

51
Q

What are the two elements that don’t follow the normal electron configuration rule for d-block elements?

A

chromium and copper

52
Q

What is the electron configuration of chromium? and why?

A

1s2 2s2 2p6 3s2 3p6 4s1 3d5 because one electron from 4s is moved up to 3d as the the 3d sub shell can hold a max. of 10 electrons, this will mean it now has 5 which is exactly half full

53
Q

What is the electron configuration of copper? and why?

A

1s2 2s2 2p6 3s2 3p6 4s1 3d10 because copper would be more stable if it has a full d sub shell. For this reason one electron from 4s is moved up to 3d. As the 3d sub shell can hold a maximum of 10 electrons, this will mean it is now full.

54
Q

What is the third exception to the normal electron configuration rule for d-block elements?

A

When d-block elements form positive ions, electrons are removed from the 4s sub shell and not the 3d shell as may be expected.

55
Q

What is the definition for ionisation energy?

A

Ionisation energy is the amount of energy needed to remove a mole of electrons from a mole of atoms, in the gaseous state.

56
Q

What are the units of ionisation energies?

A

kJmol-1

57
Q

Why do successive ionisation energies generally increase?

A

as the electron is being removed for an increasingly more positive ion

58
Q

What is the trend in ionisation energy across period 3?

A
  • general increase in IE across the period
  • this is because across period 3 there is a greater nuclear charge (more protons)
  • and the same amount of shielding
59
Q

What are the two elements that are exceptions to the general increase in IE across period 3?

A

Aluminium and Sulfur

60
Q

Explain why aluminium has a lower 1st IE than magnesium

A
  • the first electron removed from Mg is from a 3s sub level
  • the first electron removed from Al is from a 3p sub level
  • the 3s sub level is lower in energy than 3p
61
Q

As you go down any group, what happens to the nuclear charge?

A

increases

62
Q

If the nuclear charge increases as you go down a group, what would you expect to happen to the ionisation energy?

A

increase

63
Q

Why doesn’t the ionisation energy increase as you go down the group?

A
  • descending the group the atomic radius increases; this means the outer electrons are less attracted to the nucleus as they are further away
  • descending the group there is more shielding; this means there are more shells of electrons between the nucleus and the outer shell. These inner electrons mean there is less attraction from the nucleus to the outer electrons.
64
Q

State and explain the trend in atomic radius down a group.

A
  • Atomic radius increases
  • The number of shells increases so the amount of shielding increases
65
Q

What is the general trend of atomic radius across the period?

A

the atomic radius decreases as you more across the period

66
Q

What are the two reasons why atomic radius gets smaller across a period?

A
  • the nuclear charge increases which means there is a greater attraction of the electrons towards the nucleus
  • the amount of shielding across any period stays the same

Chemistry (16 decks)

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